LUMINESCENT SOLAR COLLECTOR

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is related to (219277-1 , GEPL 2 00011 ) entitled "LUMINESCENT SOLAR COLLECTOR HAVING CUSTOMIZABLE VIEWING COLOR", filed on December 22, 2006. This application is also related to (219253-1 , GEPL 2 00010) entitled "LUMINESCENT THERMOPLASTIC COMPOSITIONS AND ARTICLES WITH ENHANCED EDGE EMISSION", filed on December 22, 2006. These two related applications are hereby incorporated by reference in their entirety.

BACKGROUND

The present disclosure generally relates to luminescent solar collectors. In particular, it relates to a method of increasing the concentration of light at the edge of such a solar collector.

Luminescent solar collectors (LSCs), or luminescent solar concentrators, are beneficial for capturing solar energy for use. An LSC usually comprises a sheet, generally a molded polymer, having a surface area. Dispersed within the sheet is a fluorescent dye. When the sheet is exposed to light (radiation energy), the dye absorbs the light and emits light at a different, longer wavelength. This light is then transported, via total internal reflection, to at least one edge of the sheet. The concentration of light from a large surface area to a smaller surface area (the edge) is also known as the "edge glow" effect. Due to this effect, the amount of light (i.e. energy) available at the edge is related to the total surface area of the sheet. A light energy converter, such as a silicon photocell, can be attached to at least one edge of the LSC to convert the light energy transmitted thereto into electricity. This enables the LSC to concentrate the maximum amount of light at its edge or edges to generate more electrical power.

The construction of such an LSC leads to several technical problems. For example, the final viewing color, or appearance, of the LSC is typically the color of the fluorescent dye. Such fluorescent dyes generally have a bright red color, which is aesthetically unpleasing and limits the application of LSCs.

Additionally, the typical lifetime requirement for an LSC is 15 years or longer. Over this time period, the LSC, especially the sheet, is exposed to the elements. A typical polymer, such as polycarbonate, used to make the sheet will weather over this time period. For example, the sheet will develop haze. Haze, in particular, reduces the energy efficiency of the LSC.

Furthermore, the sheet generally must be made from a transparent polymer, such as polycarbonate (PC) or poly(methyl methacrylate) (PMMA) so the fluorescent dye can be exposed to the maximum amount of light. For some consumer applications, though, a translucent material is preferred. For example, skylights may be translucent. This translucence is similar to haze, though, and is also expected to reduce the energy efficiency of the LSC.

BRIEF DESCRIPTION

Disclosed, in various embodiments, are luminescent solar collectors which resist haze formation for extended periods of time.

The solar collector comprises a substrate, such as a sheet or panel, and a light energy converter. The light energy converter is operatively connected to the substrate. For example, the operative connection may be by glueing to the edge, mounting in a slit in the substrate, or by positioning it along the edge. The substrate comprises a fluorescent dye or quantum dot and a polymer. The polymer comprises a polycarbonate unit and a polyester unit derived from the reaction of isophthalic acid, terephthalic acid, and resorcinol (ITR).

In further embodiments, the molar concentration of the polyester unit is at least 5 mole percent. The polyester unit and the polycarbonate unit may also have a molar ratio (polyestenpolycarbonate) of from about 5:95 to about 35:65.

In other embodiments, the polymer further comprises a UV agent in a concentration of from about 0.1 weight percent to about 0.3 weight percent, based on the total weight of the polymer.

The fluorescent dye may be a perylene or terrylene. In specific embodiments, the fluorescent dye or quantum dot has a wavelength of maximum absorbance greater than 430 nanometers, and more particularly from about 800 nanometers to about 950 nanometers. In specific embodiments, the fluorescent dye or quantum dot is present in an amount of from about 0.0001 weight percent to about 1 weight percent, based on the total weight of the substrate.

In another exemplary embodiment, the substrate comprises a fluorescent layer and a covering or overcoat layer. The light energy converter is operatively connected to at least the fluorescent layer. The fluorescent layer comprises a polycarbonate polymer and a fluorescent dye or quantum dot dispersed therein. The covering or overcoat layer comprises a block copolymer having a polyester unit derived from the reaction of isophthalic acid, terephthalic acid, and resorcinol. The overcoat layer at least partially covers, and preferably fully covers, the fluorescent layer.

In further embodiments, the block copolymer comprises a molar ratio of from about 5 percent to about 35 percent of the polyester unit, based on the number of moles in the block copolymer.

The overcoat layer may have a thickness of from about 90 micrometers to about 130 micrometers. In more specific embodiments, the overcoat layer has a thickness of from about 95 micrometers to about 120 micrometers.

These and other non-limiting characteristics of the luminescent solar collectors of the disclosure are more particularly described below.

BRIEF DESCRIPTION OF THE DRAWINGS

The following is a brief description of the drawings, which are presented for the purposes of illustrating the exemplary embodiments disclosed herein and not for the purposes of limiting the same. FIGURE 1 is an elevated view of a luminescent solar collector.

FIGURE 2 is a side view of a first exemplary embodiment of the luminescent solar collector.

FIGURE 3 is a side view of a secondary exemplary embodiment of the luminescent solar collector.

DETAILED DESCRIPTION

A more complete understanding of the components, processes and apparatuses disclosed herein can be obtained by reference to the accompanying drawings. These drawings are merely schematic representations based on convenience and the ease of demonstrating the present disclosure, and are, therefore, not intended to indicate relative size and dimensions of the devices or components thereof and/or to define or limit the scope of the exemplary embodiments.

Although specific terms are used in the following description for the sake of clarity, these terms are intended to refer only to the particular structure of the embodiments selected for illustration in the drawings, and are not intended to define or limit the scope of the disclosure. In the drawings and the following description below, it is to be understood that like numeric designations refer to components of like function.

Referring to Figures 1 and 2, a luminescent solar collector (LSC) 10 comprises a sheet (or panel) 20. The sheet or panel has two opposing surfaces 30, 40. The opposing surfaces 30, 40 are joined by at least one edge 50. For the sheet depicted, there are three additional connecting edges 60, 70, 80. The sheet comprises a polymer and fluorescent dye particles 100 dispersed evenly therein. A light energy converter, such as a photocell 90, is mounted or operatively connected to the at least one connecting edge 50 to convert the light to electricity. For example, the operative connection may be made by means including, but not limited to, glueing the convertor to the edge, mounting it in a slit, or by positioning it along the edge. Edge emission may be measured in watts per square meter (WIm ² ). It is measured where the operative connection to the light energy convertor is made. In this embodiment, the edge emission is measured is at the connecting edge 50. The area in the denominator is that of the edge 50, not that of the surface 30.

As explained above, light 110 is absorbed by the fluorescent dye particles 100. The particles 100 then emit light 120 with a Stokes shift (i.e. towards a higher wavelength). The emitted light, due to total internal reflection, is guided towards the edge 50 of the sheet where the photocell 90 is located. The other edges 60, 70, 80 may be coated, for example with a mirror coating to reflect light towards edge 50 as well. An opposing surface 40 may also be coated to reflect light as well.

The sheet 20 is wide in two dimensions and thinner in the third dimension (its thickness). The opposing surfaces 30, 40 of the sheet 20 are generally parallel to each other, but need not be. It is also contemplated that the sheet 20 may be molded into various shapes. For example, the sheet may have the shape of a pyramidal frustum, a box, or as the surface of a hemisphere. The sheet may also vary in thickness. In particular embodiments, the sheet is planar. This shape is contemplated for use, for example, on the side or rooftop of a building, such as a house.

With respect to the polymers, as used herein, the term "hydrocarbyl" refers to a straight or branched chain, substituted or unsubstituted hydrocarbon group including aromatic and/or aliphatic groups; the term "alkyl" refers to a straight or branched chain monovalent hydrocarbon group; "alkylene" refers to a straight or branched chain divalent hydrocarbon group; "alkylidene" refers to a straight or branched chain divalent hydrocarbon group, with both valences on a single common carbon atom; "alkenyl" refers to a straight or branched chain monovalent hydrocarbon group having at least two carbons joined by a carbon-carbon double bond; "cycloalkyl" refers to a non-aromatic monovalent monocyclic or multicyclic hydrocarbon group having at least three carbon atoms, "cycloalkylene" refers to a non-aromatic alicyclic divalent hydrocarbon group having at least three carbon atoms, with at least one degree of unsaturation; "aryl" refers to an aromatic monovalent group containing only carbon in the aromatic ring or rings; "arylene" refers to an aromatic divalent group containing only carbon in the aromatic ring or rings; "alkylaryl" refers to an aryl group that has been substituted with an alkyl group as defined above, with 4-methylphenyl being an exemplary alkylaryl group; "arylalkyl" refers to an alkyl group that has been substituted with an aryl group as defined above, with benzyl being an exemplary arylalkyl group; "acyl" refers to a an alkyl

group as defined above with the indicated number of carbon atoms attached through a carbonyl carbon bridge (-C(=O)-); "alkoxy" refers to an alkyl group as defined above with the indicated number of carbon atoms attached through an oxygen bridge (-O-); and "aryloxy" refers to an aryl group as defined above with the indicated number of carbon atoms attached through an oxygen bridge (-O-).

Unless otherwise indicated, each of the foregoing groups may be unsubstituted or substituted, provided that the substitution does not significantly adversely affect synthesis, stability, or use of the compound. The term "substituted" as used herein means that any one or more hydrogens on the designated atom or group are replaced with another group, provided that the designated atom's normal valence is not exceeded. When the substituent is oxo (i.e., =O), then two hydrogens on the atom are replaced. Combinations of substituents and/or variables are permissible provided that the substitutions do not significantly adversely affect synthesis or use of the compound.

The sheet of the LSC comprises a polymer and a fluorescent dye. Types of thermoplastic polymers that are useful comprise polycarbonates, including homopolycarbonates, copolycarbonates, polyester-polycarbonates, and polysiloxane- polycarbonates; polyesters including poly(alkylene terephthalate); polyetherimides; polysiloxane-polyethehmides; polyphenylene ethers; polyolefins; addition polymers, including homopolymers and copolymers, especially homopolymers of alkenylaromatic compounds, such as polystyrenes, and copolymers of alkenylaromatic compounds, such as impact modified poly(alkenylaromatic) copolymers with ethylenically unsaturated nitriles, and poly(meth)acrylates.

The thermoplastic polymer can include a polycarbonate. As used herein, the terms "polycarbonate" and "polycarbonate resin" mean compositions having repeating structural carbonate units of the formula (1 ): o — R'-O— 1— o— (1 ) in which at least 60 percent of the total number of R ¹ groups are aromatic organic radicals and the balance thereof are aliphatic, alicyclic, or aromatic radicals. In one embodiment, each R ¹ is an aromatic organic radical, for example a radical of the formula (2):

-A ¹ -Y ¹ -A ^δ (2) wherein each of A ¹ and A ² is a monocyclic divalent aryl radical and Y ¹ is a bridging radical having one or two atoms that separate A ¹ from A ² . In an exemplary embodiment, one atom separates A ¹ from A ² . Illustrative non-limiting examples of radicals of this type are -O-, -S-, -S(O)-, -S(O) ₂ -, -C(O)-, methylene, cyclohexyl- methylene, 2-[2.2.1]-bicycloheptylidene, ethylidene, isopropylidene, neopentylidene, cyclohexylidene, cyclopentadecylidene, cyclododecylidene, and adamantylidene. The bridging radical Y ¹ may be a hydrocarbon group or a saturated hydrocarbon group such as methylene, cyclohexylidene, or isopropylidene.

Polycarbonates may be produced by the interfacial reaction of dihydroxy compounds having the formula HO-R ¹ -OH, which includes dihydroxy compounds of formula (3)

HO-A ¹ - Y ¹ — A ² -OH (3) wherein Y ¹ , A ¹ and A ² are as described above. Also included are bisphenol compounds of general formula (4):

wherein R ^a and R ^b each represent a halogen atom or a monovalent hydrocarbon group and may be the same or different; p and q are each independently integers of O to 4; and X ^a represents one of the groups of formula (5):

— f C — or — ϊ C ¹ —

R ^d (5) wherein R ^c and R ^d each independently represent a hydrogen atom or a monovalent linear or cyclic hydrocarbon group and R ^e is a divalent hydrocarbon group.

In an embodiment, a heteroatom-containing cyclic alkylidene group comprises at least one heteroatom with a valency of 2 or greater, and at least two carbon atoms. Heteroatoms for use in the heteroatom-containing cyclic alkylidene group include -O-, - S-, and -N(Z)-, where Z is a substituent group selected from hydrogen, hydroxy, C _M2 alkyl, C _{M 2} alkoxy, or C _M2 acyl. Where present, the cyclic alkylidene group or heteroatom-containing cyclic alkylidene group may have 3 to 20 atoms, and may be a

single saturated or unsaturated ring, or fused polycyclic ring system wherein the fused rings are saturated, unsaturated, or aromatic.

Other bisphenols containing substituted or unsubstituted cyclohexane units can be used, for example bisphenols of formula (6):

wherein each R ^f is independently hydrogen, C _{M 2} alkyl, or halogen; and each R ⁹ is independently hydrogen or C _{M 2} alkyl. The substituents may be aliphatic or aromatic, straight chain, cyclic, bicyclic, branched, saturated, or unsaturated. Such cyclohexane- containing bisphenols, for example the reaction product of two moles of a phenol with one mole of a hydrogenated isophorone, are useful for making polycarbonate polymers with high glass transition temperatures and high heat distortion temperatures. Cyclohexyl bisphenol containing polycarbonates, or a combination comprising at least one of the foregoing with other bisphenol polycarbonates, are supplied by Bayer Co. under the APEC ^® trade name.

Other useful dihydroxy compounds having the formula HO-R ¹ -OH include aromatic dihydroxy compounds of formula (7):

wherein each R ^h is independently a halogen atom, a C _MO hydrocarbyl such as a C _MO alkyl group, a halogen substituted C _MO hydrocarbyl such as a halogen-substituted C _{M 0} alkyl group, and n is 0 to 4. The halogen is usually bromine.

Exemplary dihydroxy compounds include the following: 4,4'-dihydroxybiphenyl, 1 ,6- dihydroxynaphthalene, 2,6-dihydroxynaphthalene, bis(4-hydroxyphenyl)methane, bis(4- hydroxyphenyl)diphenylmethane, bis(4-hydroxyphenyl)-1 -naphthylmethane, 1 ,2-bis(4- hydroxyphenyl)ethane, 1 ,1 -bis(4-hydroxyphenyl)-1-phenylethane, 2-(4-hydroxyphenyl)- 2-(3-hydroxyphenyl)propane, bis(4-hydroxyphenyl)phenylmethane, 2,2-bis(4-hydroxy-3- bromophenyl)propane, 1 ,1 -bis (hydroxyphenyl)cyclopentane, 1 ,1 -bis(4- hydroxyphenyl)cyclohexane, 1 ,1 -bis(4-hydroxyphenyl)isobutene, 1 ,1 -bis(4-

hydroxyphenyl)cyclododecane, trans-2,3-bis(4-hydroxyphenyl)-2-butene, 2,2-bis(4- hydroxyphenyl)adamantine, (alpha, alpha'-bis(4-hydroxyphenyl)toluene, bis(4- hydroxyphenyl)acetonitrile, 2,2-bis(3-methyl-4-hydroxyphenyl)propane, 2,2-bis(3-ethyl- 4-hydroxyphenyl)propane, 2,2-bis(3-n-propyl-4-hydroxyphenyl)propane, 2,2-bis(3- isopropyl-4-hydroxyphenyl)propane, 2,2-bis(3-sec-butyl-4-hydroxyphenyl)propane, 2,2- bis(3-t-butyl-4-hydroxyphenyl)propane, 2,2-bis(3-cyclohexyl-4-hydroxyphenyl)propane, 2,2-bis(3-allyl-4-hydroxyphenyl)propane, 2,2-bis(3-methoxy-4-hydroxyphenyl)propane, 2,2-bis(4-hydroxyphenyl)hexafluoropropane, 1 ,1-dichloro-2,2-bis(4- hydroxyphenyl)ethylene, 1 ,1 -dibromo-2,2-bis(4-hydroxyphenyl)ethylene, 1 ,1-dichloro- 2,2-bis(5-phenoxy-4-hydroxyphenyl)ethylene, 4,4'-dihydroxybenzophenone, 3,3-bis(4- hydroxyphenyl)-2-butanone, 1 ,6-bis(4-hydroxyphenyl)-1 ,6-hexanedione, ethylene glycol bis(4-hydroxyphenyl)ether, bis(4-hydroxyphenyl)ether, bis(4-hydroxyphenyl)sulfide, bis(4-hydroxyphenyl)sulfoxide, bis(4-hydroxyphenyl)sulfone, 9,9-bis(4- hydroxyphenyl)fluorine, 2,7-dihydroxypyrene, 6,6'-dihydroxy-3,3,3',3'- tetramethylspiro(bis)indane ("spirobiindane bisphenol"), 3,3-bis(4- hydroxyphenyl)phthalide, 2,6-dihydroxydibenzo-p-dioxin, 2,6-dihydroxythianthrene, 2,7- dihydroxyphenoxathin, 2,7-dihydroxy-9,10-dimethylphenazine, 3,6- dihydroxydibenzofuran, 3,6-dihydroxydibenzothiophene, and 2,7-dihydroxycarbazole, resorcinol, substituted resorcinol compounds such as 5-methyl resorcinol, 5-ethyl resorcinol, 5-propyl resorcinol, 5-butyl resorcinol, 5-t-butyl resorcinol, 5-phenyl resorcinol, 5-cumyl resorcinol, 2,4,5,6-tetrafluoro resorcinol, 2,4,5,6-tetrabromo resorcinol, or the like; catechol; hydroquinone; substituted hydroquinones such as 2- methyl hydroquinone, 2-ethyl hydroquinone, 2-propyl hydroquinone, 2-butyl hydroquinone, 2-t-butyl hydroquinone, 2-phenyl hydroquinone, 2-cumyl hydroquinone, 2,3,5,6-tetramethyl hydroquinone, 2,3,5,6-tetra-t-butyl hydroquinone, 2,3,5,6-tetrafluoro hydroquinone, 2,3,5,6-tetrabromo hydroquinone, and the like, as well as combinations comprising at least one of the foregoing dihydroxy compounds.

Specific examples of bisphenol compounds that may be represented by formula (3) include 1 ,1 -bis(4-hydroxyphenyl) methane, 1 ,1 -bis(4-hydroxyphenyl) ethane, 2,2-bis(4- hydroxyphenyl) propane (hereinafter "bisphenol-A" or "BPA"), 2,2-bis(4-hydroxyphenyl) butane, 2, 2-bis(4-hydroxyphenyl) octane, 1 ,1-bis(4-hydroxyphenyl) propane, 1 ,1 -bis(4- hydroxyphenyl) n-butane, 2,2-bis(4-hydroxy-1 -methylphenyl) propane, 1 ,1 -bis(4- hydroxy-t-butyl phenyl) propane, 3,3-bis(4-hydroxyphenyl) phthalimidine, 2-phenyl-3,3-

bis(4-hydroxyphenyl) phthalimidine (PPPBP), and 1 ,1 -bis(4-hydroxy-3- methylphenyl)cyclohexane (DMBPC). Combinations comprising at least one of the foregoing dihydroxy compounds may also be used.

In a specific embodiment, the polycarbonate is a linear homopolymer derived from bisphenol-A, in which each of A ¹ and A ² is p-phenylene and Y ¹ is isopropylidene. The polycarbonates may have an intrinsic viscosity, as determined in chloroform at 25 ⁰ C, of from about 0.3 to about 1.5 deciliters per gram (dl/g), specifically from about 0.45 to about 1.0 dl/g. The polycarbonates may have a weight average molecular weight (Mw) of from about 10,000 to about 100,000, as measured by gel permeation chromatography (GPC) using a crosslinked styrene-divinyl benzene column, at a sample concentration of 1 milligram per milliliter, and as calibrated with polycarbonate standards.

In an embodiment, the polycarbonate has a melt volume flow rate (often abbreviated MVR). The MVR measures the rate at which a thermoplastic passes vertically through a capillary under a defined weight load. The MVR is measured in cubic cm per 10 minutes (cc/10 min). Polycarbonates useful for the formation of thin articles may have an MVR, measured at 300 ⁰ C under a load of 1.2 kg according to ASTM D1238-04, of from about 0.5 to about 80 cubic centimeters per 10 minutes (cc/10 min). In a specific embodiment, a useful polycarbonate composition has an MVR measured at 300 ⁰ C under a load of 1.2 kg according to ASTM D1238-04, of from about 0.5 to about 50 cc/10 min, specifically from about 0.5 to about 25 cc/10 min, and more specifically from about 1 to about 15 cc/10 min. Mixtures of polycarbonates of different flow properties may be used to achieve the overall desired flow property.

The polycarbonate may have a light transmittance greater than or equal to about 55%, specifically greater than or equal to about 60% and more specifically greater than or equal to about 70%, as measured using a molded article of 3.2 ± 0.12 millimeters thickness and consisting of the polycarbonate, according to ASTM D1003-00. The polycarbonate may also have a haze less than or equal to about 5%, specifically less than or equal to about 4%, and most specifically less than or equal to about 3%, as

measured using a molded article of 3.2 ± 0.12 millimeters thickness and consisting of the polycarbonate, according to ASTM D1003-00.

"Polycarbonates" and "polycarbonate resins" as used herein further include homopolycarbonates, copolymers comprising different R ¹ moieties in the carbonate (referred to herein as "copolycarbonat.es"), copolymers comprising carbonate units and other types of polymer units, such as ester units, polysiloxane units, and combinations comprising at least one of homopolycarbonates and copolycarbonates. As used herein, "combination" is inclusive of blends, mixtures, alloys, reaction products, and the like. A specific type of copolymer is a polyester carbonate, also known as a polyester- polycarbonate. Such copolymers further contain, in addition to recurring carbonate chain units of the formula (1 ), repeating units of formula (8): o o O — R ² — O C Il T C Il / _g \ wherein R ² is a divalent group derived from a dihydroxy compound, and may be, for example, a C _2- io alkylene group, a C _6- 2o alicyclic group, a C _6- 2o aromatic group or a polyoxyalkylene group in which the alkylene groups contain 2 to about 6 carbon atoms, specifically 2, 3, or 4 carbon atoms; and T divalent group derived from a dicarboxylic acid, and may be, for example, a C _2- io alkylene group, a C _6- 2o alicyclic group, a C _6- 2o alkyl aromatic group, or a C _6- 2o aromatic group.

In an embodiment, R ² is a C2-30 alkylene group having a straight chain, branched chain, or cyclic (including polycyclic) structure. In another embodiment, R ² is derived from an aromatic dihydroxy compound of formula (4) above. In another embodiment, R ² is derived from an aromatic dihydroxy compound of formula (7) above.

Examples of aromatic dicarboxylic acids that may be used to prepare the polyester units include isophthalic or terephthalic acid, 1 ,2-di(p-carboxyphenyl)ethane, 4,4'- dicarboxydiphenyl ether, 4,4'-bisbenzoic acid, and combinations comprising at least one of the foregoing acids. Acids containing fused rings can also be present, such as in 1 ,4- , 1 ,5-, or 2,6-naphthalenedicarboxylic acids. Specific dicarboxylic acids are terephthalic acid, isophthalic acid, naphthalene dicarboxylic acid, cyclohexane dicarboxylic acid, or combinations thereof. A specific dicarboxylic acid comprises a combination of

isophthalic acid and terephthalic acid wherein the weight ratio of isophthalic acid to terephthalic acid is about 91 :9 to about 2:98. In another specific embodiment, R ² is a C _2- 6 alkylene group and T is p-phenylene, m-phenylene, naphthalene, a divalent cycloaliphatic group, or a combination thereof. This class of polyester includes the poly(alkylene terephthalates).

Polycarbonates can be manufactured by processes such as interfacial polymerization and melt polymerization. Although the reaction conditions for interfacial polymerization may vary, an exemplary process generally involves dissolving or dispersing a dihydhc phenol reactant in aqueous caustic soda or potash, adding the resulting mixture to a suitable water-immiscible solvent medium, and contacting the reactants with a carbonate precursor in the presence of a catalyst such as thethylamine or a phase transfer catalyst, under controlled pH conditions, e.g., about 8 to about 10. The most commonly used water immiscible solvents include methylene chloride, 1 ,2- dichloroethane, chlorobenzene, toluene, and the like.

Carbonate precursors include, for example, a carbonyl halide such as carbonyl bromide or carbonyl chloride, or a haloformate such as a bishaloformates of a dihydric phenol (e.g., the bischloroformates of bisphenol-A, hydroquinone, or the like) or a glycol (e.g., the bishaloformate of ethylene glycol, neopentyl glycol, polyethylene glycol, or the like). Combinations comprising at least one of the foregoing types of carbonate precursors may also be used. In an exemplary embodiment, an interfacial polymerization reaction to form carbonate linkages uses phosgene as a carbonate precursor, and is referred to as a phosgenation reaction.

Among the phase transfer catalysts that may be used are catalysts of the formula (R ³ ) ₄ Q ⁺ X, wherein each R ³ is the same or different, and is a C _MO alkyl group; Q is a nitrogen or phosphorus atom; and X is a halogen atom or a Ci _-8 alkoxy group or C _6- i8 aryloxy group. Useful phase transfer catalysts include, for example, [CH ₃ (CH ₂ )SkNX, [CH ₃ (CH ₂ ) _S ] ₄ PX, [CH ₃ (CH ₂ ) _S ] ₄ NX, [CH ₃ (CH ₂ ) ₆ ] ₄ NX, [CH ₃ (CH ₂ ) ₄ ] ₄ NX,

CH ₃ [CH ₃ (CH ₂ )S] ₃ NX, and CH ₃ [CH ₃ (CH ₂ ) ₂ ] ₃ NX, wherein X is Cl ^" , Br ^" , a Ci _-8 alkoxy group or a C-6-18 aryloxy group. An effective amount of a phase transfer catalyst may be about 0.1 to about 10 wt% based on the weight of bisphenol in the phosgenation mixture. In

another embodiment an effective amount of phase transfer catalyst may be about 0.5 to about 2 wt% based on the weight of bisphenol in the phosgenation mixture.

Branched polycarbonate blocks may be prepared by adding a branching agent during polymerization. These branching agents include polyfunctional organic compounds containing at least three functional groups selected from hydroxyl, carboxyl, carboxylic anhydride, haloformyl, and mixtures of the foregoing functional groups. Specific examples include trimellitic acid, trimellitic anhydride, thmellitic trichloride, tris-p-hydroxy phenyl ethane, isatin-bis-phenol, tris-phenol TC (1 ,3,5-tris((p- hydroxyphenyl)isopropyl)benzene), tris-phenol PA (4(4(1 ,1 -bis(p-hydroxyphenyl)-ethyl) alpha, alpha-dimethyl benzyl)phenol), 4-chloroformyl phthalic anhydride, thmesic acid, and benzophenone tetracarboxylic acid. The branching agents may be added at a level of about 0.05 to about 2.0 wt%. Mixtures comprising linear polycarbonates and branched polycarbonates may be used.

A chain stopper (also referred to as a capping agent) may be included during polymerization. The chain stopper controls molecular weight in the polycarbonate. Exemplary chain stoppers include certain mono-phenolic compounds, mono-carboxylic acid chlorides, and/or mono-chloroformates. Mono-phenolic chain stoppers are exemplified by monocyclic phenols such as phenol and C1-C22 alkyl-substituted phenols such as p-cumyl-phenol, resorcinol monobenzoate, and p-and tertiary-butyl phenol; and monoethers of diphenols, such as p-methoxyphenol. Alkyl-substituted phenols with branched chain alkyl substituents having 8 to 9 carbon atom may be specifically mentioned. Certain mono-phenolic UV absorbers may also be used as a capping agent, for example 4-substituted-2-hydroxybenzophenones and their derivatives, aryl salicylates, monoesters of diphenols such as resorcinol monobenzoate, 2-(2- hydroxyaryl)-benzothazoles and their derivatives, 2-(2-hydroxyaryl)-1 ,3,5-thazines and their derivatives, and the like.

Mono-carboxylic acid chlorides may also be used as chain stoppers. These include monocyclic, mono-carboxylic acid chlorides such as benzoyl chloride, C1-C22 alkyl- substituted benzoyl chloride, toluoyl chloride, halogen-substituted benzoyl chloride, bromobenzoyl chloride, cinnamoyl chloride, 4-nadimidobenzoyl chloride, and combinations thereof; polycyclic, mono-carboxylic acid chlorides such as trimellitic

anhydride chloride, and naphthoyl chloride; and combinations of monocyclic and polycyclic mono-carboxylic acid chlorides. Chlorides of aliphatic monocarboxylic acids with less than or equal to about 22 carbon atoms are useful. Functionalized chlorides of aliphatic monocarboxylic acids, such as acryloyl chloride and methacryoyl chloride, are also useful. Also useful are mono-chloroformates including monocyclic, mono- chloroformates, such as phenyl chloroformate, alkyl-substituted phenyl chloroformate, p- cumyl phenyl chloroformate, toluene chloroformate, and combinations thereof. Alternatively, melt processes may be used to make the polycarbonates. Generally, in the melt polymerization process, polycarbonates may be prepared by co-reacting, in a molten state, the dihydroxy reactant(s) and a diaryl carbonate ester, such as diphenyl carbonate, in the presence of a transesterification catalyst in a Banbury ^® mixer, twin screw extruder, or the like to form a uniform dispersion. Volatile monohydric phenol is removed from the molten reactants by distillation and the polymer is isolated as a molten residue. A specifically useful melt process for making polycarbonates uses a diaryl carbonate ester having electron-withdrawing substituents on the aryls. Examples of specifically useful diaryl carbonate esters with electron withdrawing substituents include bis(4-nitrophenyl)carbonate, bis(2-chlorophenyl)carbonate, bis(4- chlorophenyl)carbonate, bis(methyl salicyl)carbonate, bis(4-methylcarboxylphenyl) carbonate, bis(2-acetylphenyl) carboxylate, bis(4-acetylphenyl) carboxylate, or a combination comprising at least one of the foregoing. In addition, transesterification catalysts for use may include phase transfer catalysts of formula (R ³ ) ₄ Q ⁺ X above, wherein each R ³ , Q, and X are as defined above. Examples of transesterification catalysts include tetrabutylammonium hydroxide, methyltributylammonium hydroxide, tetrabutylammonium acetate, tetrabutylphosphonium hydroxide, tetrabutylphosphonium acetate, tetrabutylphosphonium phenolate, or a combination comprising at least one of the foregoing. Melt processes are generally carried out in a series of stirred tank reactors. The reaction can be carried out by either a batch mode or a continuous mode. The apparatus in which the reaction is carried out can be any suitable tank, tube, or column. Continuous processes usually involve the use of one or more continuous- stirred tank reactors (CSTRs) and one or more finishing reactors.

Polyester-polycarbonates may also be prepared by interfacial polymerization. Rather than utilizing the dicarboxylic acid per se, it is possible, and sometimes even preferred, to employ the reactive derivatives of the acid, such as the corresponding acid halides, in

particular the acid dichlorides and the acid dibromides. Thus, for example instead of using isophthalic acid, terephthalic acid, or a combination comprising at least one of the foregoing, it is possible to employ isophthaloyl dichloride, terephthaloyl dichlohde, and a combination comprising at least one of the foregoing.

In addition to the polycarbonates described above, combinations of the polycarbonate with other thermoplastic polymers, for example combinations of homopolycarbonates and/or polycarbonate copolymers with polyesters, may be used. Useful polyesters may include, for example, polyesters having repeating units of formula (8), which include poly(alkylene dicarboxylates), liquid crystalline polyesters, and polyester copolymers. The polyesters described herein are generally completely miscible with the polycarbonates when blended.

The polyesters may be obtained by interfacial polymerization or melt-process condensation as described above, by solution phase condensation, or by transestehfication polymerization wherein, for example, a dialkyl ester such as dimethyl terephthalate may be transesterified with ethylene glycol using acid catalysis, to generate poly(ethylene terephthalate). It is possible to use a branched polyester in which a branching agent, for example, a glycol having three or more hydroxyl groups or a trifunctional or multifunctional carboxylic acid has been incorporated. Furthermore, it is sometime desirable to have various concentrations of acid and hydroxyl end groups on the polyester, depending on the ultimate end use of the composition.

Useful polyesters may include aromatic polyesters, poly(alkylene esters) including poly(alkylene arylates), and poly(cycloalkylene diesters). Aromatic polyesters may have a polyester structure according to formula (8), wherein D and T are each aromatic groups as described hereinabove. In an embodiment, useful aromatic polyesters may include, for example, poly(isophthalate-terephthalate-resorcinol) esters, poly(isophthalate-terephthalate-bisphenol-A) esters, poly[(isophthalate-terephthalate- resorcinol) ester-co-(isophthalate-terephthalate-bisphenol-A)] ester, or a combination comprising at least one of these. Also contemplated are aromatic polyesters with a minor amount, e.g., about 0.5 to about 10 wt%, based on the total weight of the polyester, of units derived from an aliphatic diacid and/or an aliphatic polyol to make copolyesters. Poly(alkylene arylates) may have a polyester structure according to formula (8), wherein T comprises groups derived from aromatic dicarboxylates,

cycloaliphatic tricarboxylic acids, or derivatives thereof. Examples of specifically useful T groups include 1 ,2-, 1 ,3-, and 1 ,4-phenylene; 1 ,4- and 1 ,5- naphthylenes; cis- or trans-1 ,4-cyclohexylene; and the like. Specifically, where T is 1 ,4-phenylene, the poly(alkylene arylate) is a poly(alkylene terephthalate). In addition, for poly(alkylene arylate), specifically useful alkylene groups D include, for example, ethylene, 1 ,4- butylene, and bis-(alkylene-disubstituted cyclohexane) including cis- and/or trans-1 ,4- (cyclohexylene)dimethylene. Examples of poly(alkylene terephthalates) include poly(ethylene terephthalate) (PET), poly(1 ,4-butylene terephthalate) (PBT), and poly(propylene terephthalate) (PPT). Also useful are poly(alkylene naphthoates), such as poly(ethylene naphthanoate) (PEN), and poly(butylene naphthanoate) (PBN). A useful poly(cycloalkylene diester) is poly(cyclohexanedimethylene terephthalate) (PCT). Combinations comprising at least one of the foregoing polyesters may also be used.

Copolymers comprising alkylene terephthalate repeating ester units with other ester groups may also be useful. Useful ester units may include different alkylene terephthalate units, which can be present in the polymer chain as individual units, or as blocks of poly(alkylene terephthalates). Specific examples of such copolymers include poly(cyclohexanedimethylene terephthalate)-co-poly(ethylene terephthalate), abbreviated as PETG where the polymer comprises greater than or equal to 50 mol% of poly(ethylene terephthalate), and abbreviated as PCTG where the polymer comprises greater than 50 mol% of poly(1 ,4-cyclohexanedimethylene terephthalate).

Poly(cycloalkylene diester)s may also include poly(alkylene cyclohexanedicarboxylate)s. Of these, a specific example is poly(1 ,4-cyclohexane-dimethanol-1 ,4- cyclohexanedicarboxylate) (PCCD), having recurring units of formula (9):

wherein, as described using formula (8), R ² is a 1 ,4-cyclohexanedimethylene group derived from 1 ,4-cyclohexanedimethanol, and T is a cyclohexane ring derived from cyclohexanedicarboxylate or a chemical equivalent thereof, and may comprise the cis- isomer, the trans-isomer, or a combination comprising at least one of the foregoing isomers.

The polyester-polycarbonates may have a weight-averaged molecular weight (M _w ) of from about 1 ,500 to about 100,000, specifically from about 1 ,700 to about 50,000, and more specifically from about 2,000 to about 40,000. Molecular weight determinations are performed using gel permeation chromatography (GPC), using a crosslinked styrene-divinylbenzene column and calibrated to polycarbonate references. Samples are prepared at a concentration of about 1 mg/ml, and are eluted at a flow rate of about 1.0 ml/min.

Where used, it is desirable for a polyester-polycarbonate to have an MVR of about 5 to about 150 cc/10 min., specifically about 7 to about 125 cc/10 min, more specifically about 9 to about 110 cc/10 min, and still more specifically about 10 to about 100 cc/10 min., measured at 300 ⁰ C and a load of 1.2 kilograms according to ASTM D1238-04. Commercial polyester blends with polycarbonate are marketed under the trade name XYLEX ^® , including for example XYLEX ^® X7300, and commercial polyester- polycarbonates are marketed under the tradename LEXAN ^® SLX polymers, including for example LEXAN® SLX-9000, and are available from GE Plastics.

The polymer may also comprise a polysiloxane-polycarbonate copolymer, also referred to as a polysiloxane-polycarbonate. The polysiloxane (also referred to herein as "polydiorganosiloxane") blocks of the copolymer comprise repeating siloxane units (also referred to herein as "diorganosiloxane units") of formula (10):

wherein each occurrence of R is same or different, and is a Ci-- _I3 monovalent organic radical. For example, R may independently be a C1-C13 alkyl group, C1-C13 alkoxy group, C ₂ -Ci ₃ alkenyl group, C ₂ -Ci ₃ alkenyloxy group, C ₃ -C ₆ cycloalkyl group, C ₃ -C ₆ cycloalkoxy group, C ₆ -Ci ₄ aryl group, C ₆ -Ci ₀ aryloxy group, C ₇ -Ci ₃ arylalkyl group, C ₇ - Ci ₃ arylalkoxy group, C ₇ -Ci ₃ alkylaryl group, or C ₇ -Ci ₃ alkylaryloxy group. The foregoing groups may be fully or partially halogenated with fluorine, chlorine, bromine, or iodine, or a combination thereof. Combinations of the foregoing R groups may be used in the same copolymer.

The value of D in formula (10) may vary widely depending on the type and relative amount of each component in the polymer, the desired properties of the polymer, and like considerations. Generally, D may have an average value of 2 to 1 ,000, specifically 2 to 500, and more specifically 5 to 100. In one embodiment, D has an average value of 10 to 75, and in still another embodiment, D has an average value of 40 to 60. Where D is of a lower value, e.g., less than 40, it may be desirable to use a relatively larger amount of the polycarbonate-polysiloxane copolymer. Conversely, where D is of a higher value, e.g., greater than 40, it may be necessary to use a relatively lower amount of the polycarbonate-polysiloxane copolymer.

A combination of a first and a second (or more) polysiloxane-polycarbonate copolymer may be used, wherein the average value of D of the first copolymer is less than the average value of D of the second copolymer.

In one embodiment, the polydiorganosiloxane blocks are provided by repeating structural units of formula (11 ):

) wherein D is as defined above; each R may independently be the same or different, and is as defined above; and each Ar may independently be the same or different, and is a substituted or unsubstituted C ₆ -C ₃ O arylene radical, wherein the bonds are directly connected to an aromatic moiety. Useful Ar groups in formula (11 ) may be derived from a C ₆ -C _3O dihydroxyarylene compound, for example a dihydroxyarylene compound of formula (3), (4), or (7) above. Combinations comprising at least one of the foregoing dihydroxyarylene compounds may also be used. Specific examples of dihydroxyarylene compounds are 1 ,1 -bis(4-hydroxyphenyl) methane, 1 ,1 -bis(4-hydroxyphenyl) ethane, 2,2-bis(4-hydroxyphenyl) propane, 2,2-bis(4-hydroxyphenyl) butane, 2,2-bis(4- hydroxyphenyl) octane, 1 ,1 -bis(4-hydroxyphenyl) propane, 1 ,1 -bis(4-hydroxyphenyl) n- butane, 2,2-bis(4-hydroxy-1 -methylphenyl) propane, 1 ,1-bis(4-hydroxyphenyl) cyclohexane, bis(4-hydroxyphenyl sulphide), and 1 ,1 -bis(4-hydroxy-t-butylphenyl) propane. Combinations comprising at least one of the foregoing dihydroxy compounds may also be used.

Units of formula (11 ) may be derived from the corresponding dihydroxy compound of formula (12):

wherein R, Ar, and D are as described above. Compounds of formula (12) may be obtained by the reaction of a dihydroxyarylene compound with, for example, an alpha, omega-bisacetoxypolydiorangonosiloxane under phase transfer conditions.

In another embodiment, polydiorganosiloxane blocks comprise units of formula (13):

wherein R and D are as described above, and each occurrence of R ⁴ is independently a divalent C1-C30 alkylene, and wherein the polymerized polysiloxane unit is the reaction residue of its corresponding dihydroxy compound. In a specific embodiment, the polydiorganosiloxane blocks are provided by repeating structural units of formula (14):

wherein R and D are as defined above. Each R ⁵ in formula (14) is independently a divalent C ₂ -C ₈ aliphatic group. Each M in formula (14) may be the same or different, and may be a halogen, cyano, nitro, Ci-Cs alkylthio, d-Cs alkyl, Ci-Cs alkoxy, C ₂ -Cs alkenyl, C ₂ -Cs alkenyloxy group, C3-C8 cycloalkyl, C3-C8 cycloalkoxy, Cβ-Cio aryl, Cβ-Cio aryloxy, C ₇ -Ci ₂ arylalkyl, C ₇ -Ci ₂ arylalkoxy, C ₇ -Ci ₂ alkylaryl, or C ₇ -Ci ₂ alkylaryloxy, wherein each n is independently O, 1 , 2, 3, or 4.

In one embodiment, M is bromo or chloro, an alkyl group such as methyl, ethyl, or propyl, an alkoxy group such as methoxy, ethoxy, or propoxy, or an aryl group such as phenyl, chlorophenyl, or tolyl; R ⁵ is a dimethylene, thmethylene ortetramethylene group; and R is a Ci _-8 alkyl, haloalkyl such as trifluoropropyl, cyanoalkyl, or aryl such as phenyl, chlorophenyl or tolyl. In another embodiment, R is methyl, or a mixture of methyl and

trifl uoropropyl , or a mixture of methyl and phenyl. In still another embodiment, M is methoxy, n is one, R ⁵ is a divalent CrC ₃ aliphatic group, and R is methyl.

Units of formula (14) may be derived from the corresponding dihydroxy polydiorganosiloxane (15):

wherein R, D, M, R ⁵ , and n are as described above. Such dihydroxy polysiloxanes can be made by effecting a platinum catalyzed addition between a siloxane hydride of formula (16):

wherein R and D are as previously defined, and an aliphatically unsaturated monohydhc phenol. Useful aliphatically unsaturated monohydric phenols included, for example, eugenol, 2-allylphenol, 4-allyl-2-methylphenol, 4-allyl-2-phenylphenol, 4-allyl-2- bromophenol, 4-allyl-2-t-butoxyphenol, 4-phenyl-2-phenylphenol, 2-methyl-4- propylphenol, 2-allyl-4,6-dimethylphenol, 2-allyl-4-bromo-6-methylphenol, 2-allyl-6- methoxy-4-methylphenol and 2-allyl-4,6-dimethylphenol. Mixtures comprising at least one of the foregoing may also be used.

In an embodiment, the polysiloxane-polycarbonate may comprise polysiloxane units, and carbonate units derived from bisphenol-A, e.g., the dihydroxy compound of formula (3) in which each of A ¹ and A ² is p-phenylene and Y ¹ is isopropylidene. Polysiloxane- polycarbonates may have a weight average molecular weight of 2,000 to 100,000, specifically 5,000 to 50,000 as measured by gel permeation chromatography using a crosslinked styrene-divinyl benzene column, at a sample concentration of 1 milligram per milliliter, and as calibrated with polycarbonate standards.

The polysiloxane-polycarbonate can have a melt volume flow rate, measured at 300 ⁰ C under a load of 1.2 kg, of 1 to 50 cubic centimeters per 10 minutes (cc/10 min),

specifically 2 to 30 cc/10 min. Mixtures of polysiloxane-polycarbonates of different flow properties may be used to achieve the overall desired flow property. In an embodiment, exemplary polysiloxane-polycarbonates are marketed under the trade name LEXAN ^® EXL polycarbonates, available from GE Plastics.

In one embodiment, the polymer comprises a polycarbonate unit and a polyester unit. This polymer is also known as polyester-polycarbonate. In a specific embodiment, the polyester unit is derived from the reaction of isophthalic acid, terephthalic acid, and resorcinol (also known as an ITR resin). The polyester unit has the following structure:

where x corresponds to the molar ratio of the isophthalate, y corresponds to the molar ratio of the resorcinol, and z corresponds to the molar ratio of the terephthalate; x, y, and z adding to 100 percent of the polyester unit. Such polyester-polycarbonates are available as LEXAN® SLX from General Electric Company. The concentration of polyester (ITR) resin should be least 5%, based on the number of moles in the polymer. In further embodiments, the polyester and polycarbonate are used in a molar ratio of from about 5:95 to about 40:60 or more particularly from about 5:95 to about 35:65, depending on the properties desired. The polyester-polycarbonates may have a weight average molecular weight of from about 1 ,500 to about 100,000 or more particularly from about 2,000 to about 40,000. The polyester-polycarbonate polymer can be a copolymer, especially a block copolymer.

The polymer may further comprise an ultra-violet (UV) agent to stabilize the polymer against photodegradation. When used, the UV agent has a concentration of from about 0.1 weight percent to 0.3 weight percent, based on the total weight of the polymer. Any UV agent may be used as long as it does not significantly adversely affect the desired properties of the polymer. UV agents particularly suitable for use include UVINUL® 3030, UV5411 , benzophenones, benzotriazoles, triazines, oxanilides, and cyanoacrylates. Representative formulas of these compounds are shown below:

oxanilide tπazme

wherein Ri, R ₂ , and R3 are independently selected from alkyl or aryl; Ari and Ar ₂ are independently aryl; and X is halogen. In a specific embodiment, the polymer is a polyester-polycarbonate with a concentration of about 5 mole percent ITR resin and about 0.3 weight percent UV agent.

The sheet further comprises a fluorescent dye. The term "fluorescent" refers to the emission of light by the dye, after absorbing light radiation, at a defined wavelength (due to the Stokes shift). By comparison, a non-fluorescent dye does not absorb the energy and re-emit it at a defined wavelength, but as heat (i.e. a broad band of radiation). Any fluorescent dye can be used that does not significantly adversely affect the desired properties of the sheet.

Exemplary dyes include the daylight fluorescent-type dyes that belong to the dye families known as rhodamines, fluoresceins, coumahns, naphthalimides, benzoxanthenes, perylenes, pyrenes, acridines, or a combination comprising at least one of the foregoing. Examples include luminescent dyes such as 7-amino-4- methylcoumahn; 3-(2'-benzothiazolyl)-7-diethylaminocoumahn; 2-(4-biphenylyl)-5-(4-t- butylphenyl)-1 ,3,4-oxadiazole; 2,5-bis-(4-biphenylyl)-oxazole; 2,2'-dimethyl-p- quaterphenyl; 2,2-dimethyl-p-terphenyl; 3,5,3"",5""-tetra-t-butyl-p-quinquephenyl; 2,5- diphenylfuran; 2,5-diphenyloxazole; 4,4'-diphenylstilbene; 4-dicyanomethylene-2-methyl- 6-(p-dimethylaminostyryl)-4H-pyran; 1 ,1 '-diethyl-2,2'-carbocyanine iodide; 3,3'-diethyl- 4,4',5,5'-dibenzothiathcarbocyanine iodide; 7-dimethylamino-1 -methyl-4-methoxy-8- azaquinolone-2; 7-dimethylamino-4-methylquinolone-2; 2-(4-(4-dimethylaminophenyl)- 1 ,3-butadienyl)-3-ethylbenzothiazolium perchlorate; 3-diethylamino-7- diethyliminophenoxazonium perchlorate; 2-(1-naphthyl)-5-phenyloxazole; 2,2'-p- phenylen-bis(5-phenyloxazole); rhodamine 700; rhodamine 800; pyrene; chrysene; rubrene; coronene, or the like; perylene dyes such as those based on imido derivatives of perylene tetracarboxylic acid; or combinations comprising at least one of the foregoing dyes. Suppliers of fluorescent colorants include Radiant Color Company (Richmond, Calif.), Day-Glo Color Corp. (Cleveland, Ohio), Sun Chemical Co. (Cincinnati, Ohio). Sinloihi Co. Ltd. (Tokyo, Japan), Swada (London, England), Mikuni Color Works Ltd. (Himeji, Japan), Matsui International Co, lnc (Japan), Nippon Keiko Color Company (Japan). Specifically useful fluorescent dyes include those available under the following tradenames: Diaresin® dyes from Mitsubishi Chemical (Japan); Lumogen® dyes from BASF (Germany), Irgalite® and Maxilon® dyes from Ciba Specialty Chemicals (Germany), Macrolex® dyes from Lanxess (Germany), and Hostasol® dyes from Clahant. Typical commercially available fluorescent dyes of the above types include amino phthalate dyes such as Rhodamine BDC (C.I. 45,170), Rhodamine 6GDN extra (C.I. 45,160; Red 480), Rhodamine F5G (Red 482), Rhodamine FB (Red 540), and Rhodamine F3B (C.I.45,175); naphthalimide derivatives such as Lumogen® F Blue 650; perylene derivatives such as Lumogen® F Red 305; Lumogen® F Yellow 083; Lumogen® F Violet 570; Lumogen® F Green 850; Macrolex® Fluorescent Yellow 10GN (C.I. Solvent Yellow 160:1 ); Macrolex® Red G; Irgalite® Violet M, Maxilon® Brilliant Flavine 10GFF, Maxilon® Black FBL-01 , Maxilon® Black RM-01 , Maxilon® Blue 5G, Maxilon® Blue 5G-01 , Maxilon® Blue GRL / Pearl, Maxilon® Blue

GRL Granulated, Maxilon® Blue GRL E, Maxilon® Blue M-G, Maxilon® Blue TRL Liquid, Maxilon® Golden Yellow GL Pearls, Maxilon® Navy FRL-02, Maxilon® Red GRL -01 Pearl, Maxilon® Red GRL-E, Maxilon® Red GRL Pearls, Maxilon® Red M-4GL, Maxilon® Yellow M-3RL, and Maxilon® Yellow M-4GL; Hostasol® Red 5B (Vat Red 41 ), Hostasol® Red GG (Solvent Orange 63), and Hostasol® Yellow 3G (Solvent Yellow 98); Fluorescent yellow F6PN and Yellow Y toner; Fluorescent Red 66; fluorescein; and 9- aminoachdine. A combination comprising at least one of the foregoing fluorescent dyes may be used. In an exemplary embodiment, fluorescent dyes useful herein include Lumogen® F Blue 650, Lumogen® Red 305, and Macrolex® Fluorescent Yellow 10GN. It will be understood that numerous fluorescent dyes are available commercially and are useful herein, and that therefore the foregoing list of fluorescent dyes should be considered exemplary, and not limiting to the dyes disclosed hereinabove. The fluorescent dye is generally dispersed completely throughout the sheet.

In an embodiment, the fluorescent dyes may be covalently bonded to a polymeric backbone to provide a polymer-supported fluorescent dye, and may also be referred to as dye conjugates. Such dye conjugates are useful to provide a fluorescent dye that is predispersed, i.e., one that is distributed throughout the polymer and which can provide a maximum fluorescence due to the more uniform dispersion. Dyes which are not so dispersed may aggregate or clump, and thereby decrease the effective loading of the dye based on the desired linear relationship between the fluorescent intensity and dye loading. Further, aromatic dyes, such as for example pyrene-based dyes, can when held proximate to one another form dimeric complexes ("excimers") that can have a shifted absorbance and/or fluorescent emission wavelength and intensity relative to the parent non-dimeric dye. Distributing the fluorescent dye along a polymer backbone by covalent bonding can, in addition to the advantages enumerated hereinabove, be used as a method to reduce or eliminate excimer formation. Fluorescent dyes that are useful for preparing dye conjugates include those having reactive functional groups capable of forming a covalent bond with a useful monomer or functional polymer or functional resin. Exemplary reactive groups provided by the fluorescent dye include phenolic hydroxy, aliphatic hydroxy, aromatic amine, aliphatic amine, thiols, carboxylic acid, and carboxylate esters. It will be understood that the foregoing list of reactive groups is meant to be exemplary, and should not be limited thereto.

Further functional ization of these functional fluorescent dyes, to provide reactive derivatives, can further increase the reactive usefulness of the fluorescent dye so functionalized. Reactive substituents can be formed by covalently reacting functional agents such as, for example, reactive derivatives of (meth)acrylic acid such as (meth)acryloyl chloride; carbonyl dihalides such as phosgene; thiocarbonyl dihalides such as thiophosgene; maleic anhydride; chloroformates including alkyl, aryl, or aralkyl chloroformates, epichlorohydhn; or the like; to the above functional dyes to provide suitable reactive groups. In an exemplary embodiment, useful functionalized fluorescent dyes include functional groups such as (meth)acrylates, (meth)acrylamides, N- hydroxysuccinimidyl (NHS) esters, isocyanates, isothiocyanates, maleimides, chloroformates, anhydrides, mixed anhydrides, epoxides, and the like. Polymeric backbone supports for such dyes can include linear polymers, crosslinked polymers, dendrimers, graft copolymers, block copolymers including two or more blocks, end group modified polymers, hyperbranched copolymers, telechelic oligomers, or the like. Useful backbone polymers typically includes poly(meth)acrylic homopolymers or copolymers including poly(meth)acrylates, poly(meth)acrylamides, and the like; polyvinyl aromatic) polymers and copolymers, including polystyrenes, copolymers thereof, and the like; polyvinyl polymers such as polyvinyl acetate) or polyvinyl alcohol), copolymers thereof, and the like; poly(alkylene oxide)s, copolymers thereof, and the like. In an embodiment, the functionalized fluorescent dye is attached to a polymer by reaction of the functional dye with a complementahly functionalized polymer. In another embodiment, the functionalized fluorescent dye having a polymerizable end group such as a (meth)acrylate or epoxide can be copolymerized with other monomers or reactive oligomers to provide a polymer-supported fluorescent dye. Other polymeric backbones that may be used as backbone support include polyesters, polycarbonates, polyimides, carbohydrate materials including substituted or unsubstituted cellulosic materials, polysaccharides, dexthns, aminosugars, and the like; proteins; or a combination comprising at least one of the foregoing polymers. In an embodiment, the polymer-supported fluorescent dyes include fluorescent dyes incorporated into the polymeric backbone in an amount of 0.5 to 50 wt%, specifically 1 to 45 wt%, and more specifically 5 to 40 wt%, based on the total weight of the fluorescent dye and polymer backbone.

A fluorescent brightener can also be included with the fluorescent dye. Fluorescent brighteners include fluorescent compounds which, when combined with a dye having relatively low fluorescence, act to increase the intensity of the fluorescent emissions from the dye combination. In an embodiment, a fluorescent brightener is used in combination with a blue fluorescent dye. Exemplary fluorescent brighteners include those marketed under the tradename Uvitex® and available from Ciba Specialty Chemicals, or DIPHYL® and BLANKOPHOR® available from Lanxess. In a specific exemplary embodiment, a useful combination of a blue dye and fluorescent brightener includes Uvitex® OB, available from Ciba Specialty Chemicals, as fluorescent brightener. It will be understood that the foregoing fluorescent brightener is exemplary and should not be considered as limiting thereto. When used, a fluorescent brightener may be included in an amount of from about 0.005 weight percent to about 25 weight percent, specifically from about 0.01 weight percent to about 20 weight percent, and more specifically from about 0.015 weight percent to about 15 weight percent, based on the total weight of the layer it is in.

Perylene diimides have high quantum yields and good weatherability. In specific embodiments, at least one dye based on a perylene or terrylene structure is used. Peryleneand terrylene structures are shown below:

Perylene Terrylene

The fluorescent dye preferably has a wavelength of maximum absorbance greater than 430 nanometers. This is the highest energy area of the solar spectrum, so has the greatest amount of energy to be captured. The fluorescent dye preferably absorbs wavelengths over a large portion of the visible and near infrared spectrum (or from

about 400 nanometers to about 950 nanometers). Perylene diimides, such as Lumogen® F Red 305, available from BASF, are especially suitable for use.

The fluorescent dye is used in coloring amounts of from about 0.001 weight percent to about 1 weight percent, particularly from about 0.005 weight percent to about 0.1 weight percent, and more particularly from about 0.02 weight percent to about 0.05 weight percent, based on the total weight of the layer it is in.

Fluorescent dyes are distinguished from fluorescent pigments in that dyes are organic compounds whereas pigments are inorganic compounds. Fluorescent pigments are unsuitable and cannot replace the fluorescent dye.

Quantum dots are nanostructures, having particle sizes in the range of from about 2 nanometers to about 100 nanometers. They may be inorganic compounds, but they are suitable for coloring the thermoplastic composition. Quantum dots may be considered interchangeable with fluorescent dyes. However, to be clear, pigments having particle sizes in the micrometer range are still unsuitable.

Whether a fluorescent dye or quantum dot is used, it should have a high quantum yield. This refers to the amount of light energy that is re-emitted as light. The light energy that is not re-emitted as light is usually converted into heat, which itself will break down the dye. In specific embodiments, the fluorescent dye has a quantum yield greater than 75%. In other specific embodiments, the fluorescent dye has a quantum yield greater than 80%. In other specific embodiments, the fluorescent dye has a quantum yield greater than 90%.

Referring to FIGURE 3, in a second exemplary embodiment, the sheet 20 has a dual- layer structure, comprising a fluorescent layer 200 and an overcoat or covering layer 300. The fluorescent layer 200 comprises a polycarbonate polymer and a fluorescent dye. The overcoat layer 300 comprises an ITR resin. The overcoat layer 300 is located so that it lays between the fluorescent layer 200 and the source of radiation 400, such as the sun.

The polycarbonate polymer of the fluorescent layer may be a homopolymer or a copolymer of different polycarbonates. In one embodiment, the polycarbonate polymer

does not comprise the ITR resin as a polyester unit. The polycarbonate polymer is generally produced by the reaction of a dihydroxy compound with a dicarboxylic acid compound. This polymerization may be an interfacial polymerization or a melt polymerization.

The overcoat layer comprises an ITR resin. The ITR resin does not need to be combined with a polycarbonate, though in a specific embodiment it is. In specific embodiments, the ITR resin is present in an ITR-block-copolymer. The block copolymer comprises a molar ratio of from about 5 mole percent to about 35 mole percent of the ITR resin. In specific embodiments, the block copolymer comprises about 18 mole percent of the ITR resin. In specific embodiments, the overcoat layer does not comprise a dye or pigment. In further embodiments, the overcoat layer does not comprise a fluorescent dye.

The overcoat layer is generally from about 90 to about 130 micrometers thick, regardless of the thickness of the fluorescent layer. In more specific embodiments, the overcoat layer is from about 95 to about 120 micrometers.

In another specific embodiment, both the polycarbonate polymer of the fluorescent layer and the ITR-block-copolymer of the overcoat layer are the same polymer, which is the polycarbonate-polyester polymer previously described (the ITR resin being the polyester unit). Because the fluorescent layer is usually thicker than the overcoat layer though, the fluorescent layer is usually a simple polycarbonate for better economics.

In this exemplary embodiment, the fluorescent dye is used in coloring amounts of from about 0.001 weight percent to about 1 weight percent, particularly from about 0.005 weight percent to about 0.1 weight percent, and more particularly from about 0.02 weight percent to about 0.05 weight percent, based on the total weight of the fluorescent layer.

In the luminescent solar collector, a sheet or panel as described above is used with a photocell. The photocell converts the light energy into electrical energy. Several different types of photocells may be used. Suitable bulk technology photocells include amorphous silicon cells, multicrystalline silicon cells, and monocrystalline silicon cells.

Suitable thin film technology photocells include cadmium telluride cells, copper indium selenide cells, gallium arsenide or indium selenide cells, and copper indium gallium selenide cells. In specific embodiments, the photocell is a multicrystalline silicon photocell or a monocrystalline silicon photocell.

Generally, each type of photocell has a "sweet spot", or a range of wavelengths (light energy) which it converts most efficiently into electric energy. The fluorescent dye of the sheet or panel and/or the fluorescent layer should be selected so that the light it emits matches, as much as possible, the sweet spot of the photocell. For example, the sweet spot of a multicrystalline silicon photocell or a monocrystalline silicon photocell is from about 700 nanometers to about 1100 nanometers.

Some specific fluorescent dyes which may be used include the following, which have the listed characteristics:

The luminescent solar collector of the present disclosure resists the development of haze much better than standard polycarbonate. Hence, the energy efficiency of the LSC is not compromised over time.

In addition to the components described hereinabove, the sheet and/or the fluorescent and covering or overcoat layers may further include various other additives ordinarily incorporated with thermoplastic compositions of this type, with the proviso that the additives are selected so as not to adversely affect the desired properties of the

thermoplastic composition. Mixtures of additives may be used. Such additives may be mixed at a suitable time during the mixing of the components for forming the thermoplastic composition.

The sheet and/or the fluorescent and covering or overcoat layers may include fillers or reinforcing agents. Specifically, useful fillers as contemplated herein are visual effects fillers that possess compositional, shape and dimensional qualities useful to the reflection and/or refraction of light. Visual effect fillers include those having planar facets and can be multifaceted or in the form of flakes, shards, plates, leaves, wafers, and the like. The shape can be irregular or regular. A non-limiting example of a regular shape is a hexagonal plate. Visual effect fillers are two dimensional, plate-type fillers, wherein a particle of a plate type filler has a ratio of its largest dimension to smallest dimension of greater than or equal to 3:1 , specifically greater than or equal to 5:1 , and more specifically greater than or equal to 10:1. The largest dimension so defined can also be referred to as the diameter of the particle. Plate-type fillers have a distribution of particle diameters described by a minimum and a maximum particle diameter. The minimum particle diameter is described by the lower detection limit of the method used to determine particle diameter, and corresponds to it. A typical method of determining particle diameters is laser light scattering, which can for example have a lower detection limit for particle diameter of 0.6 nanometers. It should be noted that particles having a diameter less than the lower detection limit may be present but not observable by the method. The maximum particle diameter is typically less than the upper detection limit of the method. The maximum particle diameter herein may be less than or equal to 1 ,000 micrometers, specifically less than or equal to 500 micrometers. The distribution of particle diameters can be unimodal, bimodal, or multimodal. The diameter can be described more generally using the mean of the distribution of the particle diameters, also referred to as the mean diameter. Useful particles may have a mean diameter of 1 to 100 micrometers, specifically 5 to 75 micrometers, and more specifically 10 to 60 micrometers. The particles may also be in the form of nanoparticles, i.e., particles with a median particle size (D ₅₀ ) smaller than 100 nm as determined using light scattering methods. Specific reflective fillers have an optically dense surface exterior finish useful for reflecting incident light. Metallic and non-metallic fillers such as those based on aluminum, silver, copper, bronze, steel, brass, gold, tin, silicon, alloys of these, combinations comprising at least one of the foregoing metals, and the like, are

specifically useful. Also specifically useful are inorganic fillers prepared from a composition presenting a surface that is useful for reflecting and/or refracting incident light. In contrast to a reflective filler, a refractive filler having refractive properties can be at least partially transparent, i.e., can allow transmission of a percentage of incident light, and can provide optical properties based on reflection, refraction, or a combination of reflection and refraction of incident light. Inorganic fillers having light reflecting and/or refracting properties useful herein may include micas, alumina, silica, silicon carbide, glass, combinations comprising at least one of the foregoing inorganic fillers, and the like.

The fillers may be coated with a layer of metallic material to facilitate conductivity where desired, or surface treated with silanes to improve adhesion, dispersion, and/or optical properties with the polymeric matrix resin. Where used, fillers can be present in amounts of 0 to 90 percent by weight, based on the total weight of the layer.

The sheet and/or the fluorescent and covering or overcoat layers can include an antioxidant. Useful antioxidant additives include, for example, organophosphites such as tris(nonyl phenyl)phosphite, ths(2,4-di-t-butylphenyl)phosphite, bis(2,4-di-t- butylphenyl)pentaerythritol diphosphite, distearyl pentaerythhtol diphosphite or the like; alkylated monophenols or polyphenols; alkylated reaction products of polyphenols with dienes, such as tetrakis[methylene(3,5-di-tert-butyl-4-hydroxyhydrocinnamate )] methane, or the like; butylated reaction products of para-cresol or dicyclopentadiene; alkylated hydroquinones; hydroxylated thiodiphenyl ethers; alkylidene-bisphenols; benzyl compounds; esters of beta-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionic acid with monohydric or polyhydhc alcohols; esters of beta-(5-tert-butyl-4-hydroxy-3- methylphenyl)-propionic acid with monohydric or polyhydric alcohols; esters of thioalkyl or thioaryl compounds such as distearylthiopropionate, dilaurylthiopropionate, dithdecylthiodipropionate, octadecyl-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, pentaerythrityl-tetrakis[3-(3,5-di-tert-butyl-4-hydroxypheny l)propionate or the like; amides of beta-(3,5-di-tert-butyl-4-hydroxyphenyl)-propionic acid or the like, or combinations comprising at least one of the foregoing antioxidants. Antioxidants can be used in amounts of 0.0001 to 1 percent by weight, based on the total weight of the layer.

Useful heat stabilizer additives include, for example, organophosphites such as triphenyl phosphite, tris-(2,6-dimethylphenyl)phosphite, tris-(mixed mono-and di- nonylphenyl)phosphite orthe like; phosphonates such as dimethylbenzene phosphonate or the like, phosphates such as trimethyl phosphate, or the like, or combinations comprising at least one of the foregoing heat stabilizers. Heat stabilizers can be used in amounts of 0.0001 to 1 percent by weight, based on the total weight of the layer.

Light stabilizers and/or ultraviolet light (UV) absorbing additives may also be used. Useful light stabilizer additives include, for example, benzotriazoles such as 2-(2- hydroxy-5-methylphenyl)benzotriazole, 2-(2-hydroxy-5-tert-octylphenyl)-benzotriazole and 2-hydroxy-4-n-octoxy benzophenone, or the like, or combinations comprising at least one of the foregoing light stabilizers. Light stabilizers can be used in amounts of 0.0001 to 1 percent by weight, based on the total weight of the layer.

Useful UV absorbing additives include for example, hydroxybenzophenones; hydroxybenzothazoles; hydroxybenzothazines; cyanoacrylates; oxanilides; benzoxazinones; 2- (2H-benzothazol-2-yl)-4-(1 ,1 ,3,3-tetramethylbutyl)-phenol (CYASORB ^® 5411 ); 2-hydroxy-4-n-octyloxybenzophenone (CYASORB ^® 531 ); 2-[4,6- bis(2,4-dimethylphenyl)-1 ,3,5-triazin-2-yl]- 5-(octyloxy)-phenol (CYASORB ^® 1164); 2,2'- (1 ,4- phenylene)bis(4H-3,1-benzoxazin-4-one) (CYASORB ^® UV- 3638); 1 ,3-bis[(2- cyano-3,3-diphenylacryloyl)oxy]-2,2-bis[[(2-cyano-3, 3- diphenylacryloyl)oxy]methyl]propane (UVINUL ^® 3030); 2,2'-(1 ,4-phenylene) bis(4H-3,1- benzoxazin-4-one); 1 ,3-bis[(2-cyano-3,3-diphenylacryloyl)oxy] -2,2-bis[[(2-cyano-3,3- diphenylacryloyl)oxy]methyl] propane; nano-size inorganic materials such as titanium oxide, cerium oxide, and zinc oxide, all with particle size less than 100 nanometers; or the like, or combinations comprising at least one of the foregoing UV absorbers. UV absorbers can be used in amounts of 0.0001 to 1 percent by weight, based on the total weight of the layer.

Plasticizers, lubricants, and/or mold release agents additives may also be used. There is considerable overlap among these types of materials, which include, for example, phthalic acid esters such as dioctyl-4,5-epoxy-hexahydrophthalate; tris- (octoxycarbonylethyl)isocyanurate; thsteahn; di- or polyfunctional aromatic phosphates such as resorcinol tetraphenyl diphosphate (RDP), the bis(diphenyl) phosphate of

hydroquinone and the bis(diphenyl) phosphate of bisphenol-A; poly-alpha-olefins; epoxidized soybean oil; silicones, including silicone oils; esters, for example, fatty acid esters such as alkyl stearyl esters, e.g., methyl stearate; stearyl stearate, pentaerythritol tetrastearate, and the like; mixtures of methyl stearate and hydrophilic and hydrophobic nonionic surfactants comprising polyethylene glycol polymers, polypropylene glycol polymers, and copolymers thereof, e.g., methyl stearate and polyethylene-polypropylene glycol copolymers in a suitable solvent; waxes such as beeswax, montan wax, paraffin wax or the like. Such materials can be used in amounts of 0.001 to 1 percent by weight, based on the total weight of the layer.

The sheet and/or the fluorescent and covering or overcoat layers can include antistatic agents. The term "antistatic agent" refers to monomeric, oligomehc, or polymeric materials that can be processed into polymer resins and/or sprayed onto materials or articles to improve conductive properties and overall physical performance. Examples of monomeric antistatic agents include glycerol monostearate, glycerol distearate, glycerol thstearate, ethoxylated amines, primary, secondary and tertiary amines, ethoxylated alcohols, alkyl sulfates, alkylarylsulfat.es, alkylphosphates, alkylaminesulfates, alkyl sulfonate salts such as sodium stearyl sulfonate, sodium dodecylbenzenesulfonate or the like, quaternary ammonium salts, quaternary ammonium resins, imidazoline derivatives, sorbitan esters, ethanolamides, betaines, or the like, or combinations comprising at least one of the foregoing monomeric antistatic agents.

Exemplary polymeric antistatic agents include certain polyesteramides polyether- polyamide (polyetheramide) block copolymers, polyetheresteramide block copolymers, polyetheresters, or polyurethanes, each containing polyalkylene glycol moieties polyalkylene oxide units such as polyethylene glycol, polypropylene glycol, polytetramethylene glycol, and the like. Such polymeric antistatic agents are commercially available, for example Pelestat ^® 6321 (Sanyo) or Pebax ^® MH1657 (Atofina), Irgastat ^® P18 and P22 (Ciba-Geigy). Other polymeric materials that may be used as antistatic agents are inherently conducting polymers such as polyaniline (commercially available as PAN I PO L ^® E B from Panipol), polypyrrole, and polythiophenes such as for example poly(3,4-ethylenedioxythiophene) (commercially available from H. C. Stark), which retain some of their intrinsic conductivity after melt processing at

elevated temperatures. In one embodiment, carbon fibers, carbon nanofibers, carbon nanotubes, carbon black, or any combination of the foregoing may be used in a polymeric resin containing chemical antistatic agents to render the composition electrostatically dissipative. Antistatic agents can be used in amounts of 0.0001 to 5 percent by weight, based on the total weight of the layer.

The sheet and/or the fluorescent and covering or overcoat layers can include flame retardants. Flame retardant that may be added may be organic compounds that include phosphorus, bromine, and/or chlorine. Non-brominated and non-chlorinated phosphorus-containing flame retardants may be preferred in certain applications for regulatory reasons, for example organic phosphates and organic compounds containing phosphorus-nitrogen bonds. Inorganic flame retardants may also be used.

One type of exemplary organic phosphate is an aromatic phosphate of the formula (GO) ₃ P=O, wherein each G is independently an alkyl, cycloalkyl, aryl, alkylaryl, or arylalkyl group, provided that at least one G is an aromatic group. Two of the G groups may be joined together to provide a cyclic group, for example, diphenyl pentaerythritol diphosphate. Other useful aromatic phosphates may be, for example, phenyl bis(dodecyl) phosphate, phenyl bis(neopentyl) phosphate, phenyl bis(3,5,5'- trimethylhexyl) phosphate, ethyl diphenyl phosphate, 2-ethylhexyl di(p-tolyl) phosphate, bis(2-ethylhexyl) p-tolyl phosphate, tritolyl phosphate, bis(2-ethylhexyl) phenyl phosphate, tri(nonylphenyl) phosphate, bis(dodecyl) p-tolyl phosphate, dibutyl phenyl phosphate, 2-chloroethyl diphenyl phosphate, p-tolyl bis(2,5,5'-trimethylhexyl) phosphate, 2-ethylhexyl diphenyl phosphate, or the like. A specific aromatic phosphate is one in which each G is aromatic, for example, thphenyl phosphate, thcresyl phosphate, isopropylated triphenyl phosphate, and the like.

Di- or polyfunctional aromatic phosphorus-containing compounds are also useful, for example, compounds of the formulas below:

wherein each G ¹ is independently a hydrocarbon having 1 to 30 carbon atoms; each G ² is independently a hydrocarbon or hydrocarbonoxy having 1 to 30 carbon atoms; each X ^a is independently a hydrocarbon having 1 to 30 carbon atoms; each X is independently a bromine or chlorine; m is O to 4, and n is 1 to 30. Examples of useful di- or polyfunctional aromatic phosphorus-containing compounds include resorcinol tetraphenyl diphosphate (RDP), the bis(diphenyl) phosphate of hydroquinone and the bis(diphenyl) phosphate of bisphenol-A, respectively, their oligomehc and polymeric counterparts, and the like.

Exemplary flame retardant compounds containing phosphorus-nitrogen bonds include phosphonithlic chloride, phosphorus ester amides, phosphoric acid amides, phosphonic acid amides, phosphinic acid amides, tris(aziridinyl) phosphine oxide. When present, phosphorus-containing flame retardants can be present in amounts of 0.1 to 10 percent by weight, based on the total weight of the layer.

Halogenated materials may also be used as flame retardants, for example halogenated compounds and resins of formula (31 ):

wherein R is an alkylene, alkylidene or cycloaliphatic linkage, e.g., methylene, ethylene, propylene, isopropylene, isopropylidene, butylene, isobutylene, amylene, cyclohexylene, cyclopentylidene, or the like; or an oxygen ether, carbonyl, amine, or

a sulfur containing linkage, e.g., sulfide, sulfoxide, sulfone, or the like. R can also consist of two or more alkylene or alkylidene linkages connected by such groups as aromatic, amino, ether, carbonyl, sulfide, sulfoxide, sulfone, or the like.

Ar and Ar' in formula (31 ) are each independently mono- or polycarbocyclic aromatic groups such as phenylene, biphenylene, terphenylene, naphthylene, or the like. Also in formula (31 ), Y is an organic, inorganic, or organometallic radical, for example: halogen, e.g., chlorine, bromine, iodine, fluorine; ethergroups of the general formula OE, wherein E is a monovalent hydrocarbon radical similar to X; monovalent hydrocarbon groups of the type represented by R; or other substituents, e.g., nitro, cyano, and the like, said substituents being essentially inert provided that there is at least one and preferably two halogen atoms per aryl nucleus.

When present, each X is independently a monovalent hydrocarbon group, for example an alkyl group such as methyl, ethyl, propyl, isopropyl, butyl, decyl, or the like; an aryl groups such as phenyl, naphthyl, biphenyl, xylyl, tolyl, or the like; and arylalkyl group such as benzyl, ethylphenyl, or the like; a cycloaliphatic group such as cyclopentyl, cyclohexyl, or the like. The monovalent hydrocarbon group may itself contain inert substituents.

Each d is independently 1 to a maximum equivalent to the number of replaceable hydrogens substituted on the aromatic rings comprising Ar or Ar'. Each e is independently 0 to a maximum equivalent to the number of replaceable hydrogens on R. Each a, b, and c is independently a whole number, including 0. When b is not 0, neither a nor c may be 0. Otherwise either a or c, but not both, may be 0. Where b is 0, the aromatic groups are joined by a direct carbon-carbon bond.

The hydroxyl and Y substituents on the aromatic groups, Ar and Ar', can be varied in the ortho, meta or para positions on the aromatic rings and the groups can be in any possible geometric relationship with respect to one another.

Included within the scope of the above formula are bisphenols of which the following are representative: 2,2-bis-(3,5-dichlorophenyl)-propane; bis-(2-chlorophenyl)-methane; bis(2,6-dibromophenyl)-methane; 1 ,1-bis-(4-iodophenyl)-ethane; 1 ,2-bis-(2,6- dichlorophenyl)-ethane; 1 ,1 -bis-(2-chloro-4-iodophenyl)ethane; 1 ,1 -bis-(2-chloro-4-

methylphenyl)-ethane; 1 ,1 -bis-(3,5-dichlorophenyl)-ethane; 2,2-bis-(3-phenyl-4- bromophenyl)-ethane; 2,6-bis-(4,6-dichloronaphthyl)-propane; 2,2-bis-(2,6- dichlorophenyl)-pentane; 2,2-bis-(3,5-dibromophenyl)-hexane; bis-(4-chlorophenyl)- phenyl-methane; bis-(3,5-dichlorophenyl)-cyclohexylmethane; bis-(3-nitro-4- bromophenyl)-nnethane; bis-(4-hydroxy-2,6-dichloro-3-methoxyphenyl)-nnethane; and 2,2-bis-(3,5-dichloro-4-hydroxyphenyl)-propane 2,2 bis-(3-bromo-4-hydroxyphenyl)- propane. Also included within the above structural formula are: 1 ,3-dichlorobenzene, 1 ,4-dibromobenzene, 1 ,3-dichloro-4-hydroxybenzene, and biphenyls such as 2,2'- dichlorobiphenyl, polybrominated 1 ,4-diphenoxybenzene, 2,4'-dibromobiphenyl, and 2,4'-dichlorobiphenyl as well as decabromo diphenyl oxide, and the like.

Also useful are oligomeric and polymeric halogenated aromatic compounds, such as a copolycarbonate of bisphenol-A and tetrabromobisphenol-A and a carbonate precursor, e.g., phosgene. Metal synergists, e.g., antimony oxide, may also be used with the flame retardant. When present, halogen containing flame retardants can be present in amounts of 0.1 to 10 percent by weight, based on the total weight of the layer.

The sheet and/or the fluorescent and covering or overcoat layers can include an anti- drip agent. Anti-drip agents may be, for example, a fibril forming or non-fibril forming fluoropolymer such as polytetrafluoroethylene (PTFE). The anti-drip agent may be encapsulated by a rigid copolymer as described above, for example styrene-acrylonithle copolymer (SAN). PTFE encapsulated in SAN is known as TSAN. Encapsulated fluoropolymers may be made by polymerizing the encapsulating polymer in the presence of the fluoropolymer, for example an aqueous dispersion. TSAN may provide significant advantages over PTFE, in that TSAN may be more readily dispersed in the composition. A useful TSAN may comprise, for example, 50 wt% PTFE and 50 wt% SAN, based on the total weight of the encapsulated fluoropolymer. The SAN may comprise, for example, 75 wt% styrene and 25 wt% acrylonitrile based on the total weight of the copolymer. Alternatively, the fluoropolymer may be pre-blended in some manner with a second polymer, such as for, example, an aromatic polycarbonate resin or SAN to form an agglomerated material for use as an anti-drip agent. Either method may be used to produce an encapsulated fluoropolymer. Antidhp agents can be used in amounts of 0.1 to 5 percent by weight, based on the total weight of the layer.

The sheet and/or the fluorescent and covering or overcoat layers may further comprise an ionizing radiation stabilizing additive. Exemplary ionizing radiation stabilizing additives include certain aliphatic alcohols, aromatic alcohols, aliphatic diols, aliphatic ethers, esters, diketones, alkenes, thiols, thioethers and cyclic thioethers, sulfones, dihydroaromatics, diethers, nitrogen compounds, or a combination comprising at least one of the foregoing. Alcohol-based stabilizing additives may be selected from mono, di-, or polysubstituted alcohols, and can be straight, branched, cyclic and/or aromatic. Useful aliphatic alcohols may include alkenols with sites of unsaturation, examples of which include 4-methyl-4-penten-2-ol, 3-methyl-pentene-3-ol, 2-methyl-4-penten-2-ol, 2,4-dimethyl-4-penten-2-ol, 2-phenyl-4-penten-2-ol, and 9-decen-1 -ol; tertiary alcohols including 3-hydroxy-3-methyl-2-butanone, 2-phenyl-2-butanol, and the like; hydroxy- substituted tertiary cycloaliphatics such as 1-hydroxy-1-methyl-cyclohexane; and hydroxymethyl aromatics having an aromatic ring with carbinol substituents such as a methylol group (-CH ₂ OH) or a more complex hydrocarbon group such as (-CRHOH) or (-CR2OH), wherein R is straight chain C1-C20 alkyl or branched C1-C20 alkyl. Exemplary hydroxy carbinol aromatics include benzhydrol, 2-phenyl-2-butanol, 1 ,3- benzenedimethanol, benzyl alcohol, 4-benzyloxy-benzyl alcohol, and 4-benzyl-benzyl alcohol.

Useful classes of ionizing radiation stabilizing additives are di- and polyfunctional aliphatic alcohols, also referred to as aliphatic diols and aliphatic polyols. Specifically useful are aliphatic diols of formula (32):

HO-(C(A')(A")) _d -S-(C(B')(B")) _e -OH (32) wherein A', A", B', and B" are each independently H or CrC ₆ alkyl; S is C1-C20 alkyl, C ₂ - C20 alkyleneoxy, C3-C6 cycloalkyl, or C3-C6 substituted cycloalkyl; and d and e are each 0 or 1 , with the proviso that, when d and e are each 0, S is selected such that both -OH groups are not connected directly to a single common carbon atom.

In formula (32), A', A", B', and B" can each be independently selected from H, methyl, ethyl, n-propyl, isopropyl, n-butyl, sec-butyl, t-butyl, n-pentyl, 2-pentyl, 3-pentyl, isopentyl, neopentyl, n-hexyl, 2-hexyl, 3-hexyl, 2-methyl pentyl, 3-methylpentyl, 2,2- dimethylbutyl, 2,3-dimethylbutyl, and the like, and a combination comprising at least one of the foregoing alkyl groups.

Spacer group S can be selected from methanediyl, ethanediyl, 1 ,1-ethanediyl, 1 ,1 - propanediyl, 1 ,2-propanediyl, 1 ,3-propanediyl, 2,2-propanediyl, 1 ,1 -butanediyl, 1 ,2- butanediyl, 1 ,3-butanediyl, 1 ,4-butanediyl, 2,2-butanediyl, 2,3-butanediyl, 1 ,1 - pentanediyl, 1 ,2- pentanediyl, 1 ,3- pentanediyl, 1 ,4- pentanediyl, 1 ,5- pentanediyl, 2,2- pentanediyl, 2,3- pentanediyl, 2,4- pentanediyl, 3,3- pentanediyl, 2-methyl-1 ,1 - butanediyl, 3-methyl-1 ,1 -butanediyl, 2-methyl-1 ,2-butanediyl, 2-methyl-1 ,3-butanediyl, 2- methyl-1 ,4-butanediyl, 2-methyl-2,2-butanediyl, 2-methyl-2,3-butanediyl, 2,2-dimethyl- 1 ,1-propanediyl, 2,2-dimethyl-1 ,2-propanediyl, 2,2-dimethyl-1 ,3-propanediyl, 3,3- dimethyl-1 ,1 -propanediyl, 3,3-dimethyl-1 ,2-propanediyl, 3,3-dimethyl-2,2-propanediyl, 1 ,1-dimethyl-2,3-propanediyl, 3,3-dimethyl-2,2-propanediyl, 1 ,1 -hexanediyl, 1 ,2- hexanediyl, 1 ,3- hexanediyl, 1 ,4- hexanediyl, 1 ,5- hexanediyl, 1 ,6- hexanediyl, 2,2- hexanediyl, 2,3- hexanediyl, 2,4- hexanediyl, 2,5- hexanediyl, 3,3- hexanediyl, 2-methyl- 1 ,1 -pentanediyl, 3-methyl-1 ,1 -pentanediyl, 2-methyl-1 ,2-pentanediyl, 2-methyl-1 ,3- pentanediyl, 2-methyl-1 ,4-pentanediyl, 2-methyl-2,2-pentanediyl, 2-methyl-2,3- pentanediyl, 2-methyl-2,4-pentanediyl, 2, 2-dimethyl-1 ,1 -butanediyl, 2, 2-dimethyl-1 ,2- butanediyl, 2,2-dimethyl-1 ,3-butanediyl, 3,3-dimethyl-1 ,1 -butanediyl, 3,3-dimethyl-1 ,2- butanediyl, 3,3-dimethyl-2,2-butanediyl, 1 ,1 -dimethyl-2,3-butanediyl, 3,3-dimethyl-2,2- butanediyl, and the like; isomers of octanediyl, decanediyl, undecanediyl, dodecanediyl, hexadecanediyl, octadecanediyl, icosananediyl, and docosananediyl; and substituted and unsubstituted cyclopropanediyl, cyclobutanediyl, cyclopentanediyl, cyclohexanediyl, wherein substituents may be the points of radical attachment, such as in 1 ,4- dimethylenecyclohexane, or may include branched and straight chain alkyl, cycloalkyl, and the like. Additionally, the spacer group S may be selected from one or more diradicals comprising polyalkyleneoxy units, such as ethyleneoxy, 1 ,2-propyleneoxy, 1 ,3-propyleneoxy, 1 ,2-butyleneoxy, 1 ,4-butyleneoxy, 1 ,6-hexyleneoxy, and the like; and a combination comprising at least one of these.

Specific examples of useful aliphatic diols include ethylene glycol, propylene glycol, 1 ,3- propanediol, 1 ,2-butanediol, 1 ,4-butanediol, meso-2,3-butanediol, 1 ,2-pentanediol, 2,3- pentanediol, 1 ,4-pentanediol, 1 ,4-hexandiol, and the like; alicyclic alcohols such as 1 ,3- cyclobutanediol, 2,2,4,4-tetramethylcyclobutanediol, 1 ,2-cyclopentanediol, 1 ,2- cyclohexanediol, 1 ,3-cyclohexanediol, 1 ,4-cyclohexanediol, 1 ,4-dimethylolcyclohexane, and the like; branched acyclic diols such as 2,3-dimethyl-2,3-butanediol (pinacol), and 2- methyl-2,4-pentanediol (hexylene glycol); and polyalkyleneoxy-containing alcohols such

as polyethylene glycol, polypropylene glycol, block or random poly(ethyleneglycol-co- propyleneglycols), and diols of copolymers containing polyalkyleneoxy-groups. Useful polyols may include polyaryleneoxy compounds such as polyhydroxystyrene; alkyl polyols such as polyvinylalcohol, polysaccharides, and esterified polysaccharides. A combination comprising at least one of the foregoing may also be useful. Specifically useful diols include 2-methyl-2,4-pentanediol (hexylene glycol), polyethylene glycol, and polypropylene glycol.

Useful aliphatic ethers may include alkoxy-substituted cyclic or acyclic alkanes such as, for example, 1 ,2-dialkoxyethanes, 1 ,2-dialkoxypropanes, 1 ,3-dialkoxypropanes, alkoxycyclopentanes, alkoxycyclohexanes, and the like. Ester compounds (-COOR) may be useful as stabilizers wherein R may be a substituted or unsubstituted, aromatic or aliphatic, hydrocarbon and the parent carboxy compound may likewise be substituted or unsubstituted, aromatic or aliphatic, and/or mono- or polyfunctional. When present, substituents may include, for example, Ci-Cs alkyl, Ci-Cs alkyl ether, C6-C20 aryl, and the like. Esters which have proven useful include tetrakis(methylene [3,5-di-t-butyl-4- hydroxy-hydrocinnamate])methane, 2,2'-oxamido bis(ethyl-3-(3,5-d i-t-butyl-4- hydroxyphenyl) propionate, and trifunctional hindered phenolic ester compounds such as GOOD-RITE ^® 3125, available from B. F. Goodrich in Cleveland OH. Diketone compounds may also be used, specifically those having two carbonyl functional groups and separated by a single intervening carbon atoms such as, for example 2,4-pentadione.

Sulfur-containing compounds, useful for use as stabilizing additives, can include thiols, thioethers and cyclic thioethers. Thiols include, for example, 2-mercaptobenzothiazole; thioethers include dilaurylthiopropionate; and cyclic thioethers include 1 ,4-dithiane, 1 ,4,8,11 -tetrathiocyclotetradecane. Cyclic thioethers containing more than one thioether group are useful, specifically those having a single intervening carbon between two thioether groups such as in, for example, 1 ,3-dithiane. The cyclic ring may contain oxygen or nitrogen members.

Aryl or alkyl sulfone stabilizing additives of general structure R-S(O)2-R' may also be used, where R and R' comprise C1-C20 alkyl, C6-C20 aryl, C1-C20 alkoxy, C6-C20 aryloxy, substituted derivatives thereof, and the like, and wherein at least one of R or R' is a

substituted or unsubstituted benzyl. When present, substituents may include, for example, CrC ₈ alkyl, CrC ₈ alkyl ether, C ₆ -C ₂ O aryl, and the like. An example of a specifically useful sulfone is benzylsulfone.

Hydroaromatic compounds may also be useful as stabilizing additives, including partially hydrogenated aromatics, and aromatics in combination with an unsaturated ring. Specific aromatics include benzene and/or naphthalene based systems. Examples of hydroaromatic compounds include indane, 5,6,7,8-tetrahydro-1-naphthol, 5,6,7,8- tetrahydro-2-naphthol, 9,10-dihydroanthracene, 9,10-dihydrophenanthrene, 1 -phenyl-1- cyclohexane, 1 ,2,3,4-tetrahydro-1 -naphthol, and the like, or a combination comprising at least one of the foregoing.

Diethers, including hydrogenated and nonhydrogenated, and substituted and unsubstituted pyrans, may also be used as stabilizing additives. When present, substituents may include Ci-C ₈ alkyl, CrC ₈ alkyl ether, or C6-C20 aryl. The pyrans may have substituents including C1-C20 alkyl, C6-C2o aryl, Ci-C2o alkoxy, or C6-C20 aryloxy, and which may be positioned on any carbon of the pyran ring. Specifically useful substituent groups include C1-C20 alkoxy or C ₆ -C ₂ O aryloxy, located on the ring at the six position. Hydrogenated pyrans are specifically useful. Examples of diethers include dihydropyranyl ethers and tetrahydropyranyl ethers.

Nitrogen compounds which may function as stabilizers include high molecular weight oxamide phenolics, for example, 2,2-oxamido bis-[ethyl 3-(3,5-d i-tert-butyl-4- hydroxyphenyl)propionate], high molecular weight oxalic anilides and their derivatives, and amine compounds such as thiourea.

Ionizing radiation stabilizing additives are typically used in amounts of 0.001 to 1 wt%, specifically 0.005 to 0.75 wt%, more specifically 0.01 to 0.5 wt%, and still more specifically 0.05 to 0.25 wt%, based on the total weight of the layer. In an embodiment, a specifically useful ionizing radiation stabilizing additive is an aliphatic diol.

Consequently, examples of non-limiting additives that may be included in the sheet and/or the polymer layers include optical effects filler, antioxidant, heat stabilizer, light stabilizer, ultraviolet light absorber, plasticizer, mold release agent, lubricant, antistatic

agent, flame retardant, anti-drip agent, gamma stabilizer, or a combination comprising at least one of the foregoing additives.

The sheet and/or polymer layers may be manufactured by methods generally available in the art. For example, in one embodiment, in one manner of proceeding, powdered polycarbonate and fluorescent dye are first blended in a HENSCHEL-Mixer® high speed mixer. Other low shear processes including but not limited to hand mixing may also accomplish this blending. The blend is then fed into the throat of an extruder via a hopper. Alternatively, one or more of the components may be incorporated into the composition by feeding directly into the extruder at the throat and/or downstream through a sidestuffer. Additives may also be compounded into a masterbatch with a desired polymeric resin and fed into the extruder. The extruder is generally operated at a temperature higher than that necessary to cause the composition to flow. The extrudate is immediately quenched in a water batch and pelletized. The pellets, so prepared, when cutting the extrudate may be one-fourth inch long or less as desired. Such pellets may be used for subsequent molding, shaping, or forming. The sheet and/or polymer layers may be molded from the thermoplastic composition by a variety of means such as injection molding, extrusion, rotational molding, blow molding and thermoforming. In a specific embodiment, molding is done by injection molding.

In the sheet having a dual-layer structure, the overcoat layer may also be applied to the fluorescent layer. An overcoat solution can be prepared by any suitable conventional technique such as, for example, by mixing the solvent with the polymeric material. The overcoat layer may be applied by any suitable application method. Non-limiting examples of suitable application methods include, for example, hand coating, spray coating, web coating, dip coating, and the like. Drying of the deposited coating can be effected by any suitable conventional technique such as, for example, oven drying, infrared radiation drying, air drying, and the like. The processing speed, drying temperature, and drying time are selected such that the overcoat layer has less than about 1 % percent solvent remaining in the layer after drying.

The following examples are provided to illustrate the luminescent solar collectors of the present disclosure. The examples are merely illustrative and are not intended to limit

devices made in accordance with the disclosure to the materials, conditions, or process parameters set forth therein. All parts are percentages by volume unless otherwise indicated.

EXAMPLES

REFERENCE EXAMPLE

A polycarbonate LSC equipped with two silicon photocells is able to convert 3-3.5% of the solar light into electricity. A reference sample containing polycarbonate with 0.05 weight percent heat stabilizer and 0.02 weight percent Lumogen® F Red 300 (from BASF) was compounded and molded into a plaque of 3.2mm thickness. The sample was subjected to artificial weathering according to ISO4892-2A corresponding to a time of 3172 hours and the haze was measured according to ASTM D1003-00. The edge emission, a measure for optical and electrical efficiency, was also measured. The results are shown in Table 1.

Table 1.

SINGLE LAYER EXAMPLE

Next, several plaques were produced of polyester-polycarbonate resin having various amounts of ITR resin and UV agent, as shown in Table 2. These plaques had a thickness of 2.5mm. These plaques were also weathered (ISO4892-2A) corresponding to a time of 2500 hours, then measured for haze (ASTM D1003-00). The results are shown in Table 2.

Table 2.

The data showed that the combinations of ITR resin with UV agent significantly reduced the amount of haze forming over a significant period of time. Increasing the ITR concentration beyond 15 mole percent did not improve haze resistance dramatically. The data also showed that the ITR resin could be included in the substrate material.

DUAL-LAYER EXAMPLE

Next, two polycarbonate plaques comprising 0.05 weight percent Lumogen® F Red 300 were made. One was covered with an overcoat layer 120 micrometers thick, the overcoat layer containing 18 mole percent ITR resin. The plaques were weathered (ISO4892-2A) corresponding to a time of 3172 hours, then measured for haze (ASTM D1003-00). The results are shown in Table 3.

Table 3.

The data showed that the overcoat layer significantly reduced the haze that formed in the polycarbonate layer underneath the overcoat layer.

In the Examples, the plaques were weathered for a time period corresponding to about 3.5 to 4.5 months. Based on the results, it is expected that the luminescent solar collectors of the present disclosure can withstand the elements for periods of 10 to 15 years without a significant increase in haze. In turn, this means the edge emission should also remain high over the 10 to 15 year time period.

The luminescent solar collector of the present disclosure has been described with reference to exemplary embodiments. Obviously, modifications and alterations will occur to others upon reading and understanding the preceding detailed description. It is intended that the exemplary embodiments be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.