HIGH-HUMIDITY, TEMPERATURE-RESPONSIVE FILM AND SELF

REGULATING WINDOW USING THE FILM

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the priority to and the benefit of EP 18205371.0, filed November 9, 2018, which is incorporated by reference herein in its entirety.

BACKGROUND

[0001] This disclosure relates to temperature-responsive films chemisorbed to a substrate. The films are useful for smart window applications.

[0002] In the building envelopes of the Western world, more than 50% of the energy consumed is devoted to cooling, heating, and lighting. Absorption of sunlight, especially of infrared (IR) wavelengths (700 to 2500 nanometers), is responsible for much of the overheating of public offices, automotive interiors, greenhouses, and similar spaces. A number of technologies have been developed to maintain indoor temperatures, although many of these are static, i.e., do not adjust their properties in response to an external trigger. Examples include static IR-regulating windows that rely on dyes, metallic nanolayers, reflecting technology such as multi-layer polymer films, or hybrid organic-inorganic Bragg’s reflectors. Electrically responsive windows are also available, most of them making use of materials such as liquid crystals, electrochromic molecules, or suspended particle device that are encapsulated between two glass or plastic plates with electrodes. However, electrically responsive windows are generally responsive to a user, rather than an external change in condition. Temperature- responsive windows based on hydrogels, phase change materials (PCMs), or holographic polymers dispersed in liquid crystals are also known, although these responsive materials are also often sandwiched between two substrates.

[0003] Accordingly, there remains a need in the art for temperature-responsive layered articles and methods for use in windows, in particular where the response is autonomous, i.e., does not require user input. Liquid crystal polymers (LCPs) are responsive to small changes in external conditions, such as temperature, that can trigger phase transitions that cause significant changes in their macroscopic properties. LCPs can be used as coatings on transparent substrates such as glass or polycarbonate, but often have poor adhesion to substrates to such substrates, e.g., physical adsorption. The adhesion can be improved by chemisorption, which includes covalent chemical linkages between the substrate and the coating. A simple process for chemical binding of LCP films to substrates has been described in WO 2018/122719, which is based on use of a primer layer containing a Type II photoinitiator. The photoinitiator induces co-reaction with the surface of the substrate and the coating composition used to form the LCP film. This process does not require surface pre-activation by plasma or corona treatment, the

polymerization can be conducted at room temperature and atmospheric pressure, with or without a solvent, and with conventional equipment.

[0004] Nonetheless, there remains a need in the art for improved temperature-responsive layered articles, in particular layered articles having a broadband response. Such articles could be used as a temperature responsive component in self-regulating windows.

SUMMARY

[0005] Disclosed herein is a layered article, comprising a copolymer substrate comprising a Type II photoinitiator covalently linked to the copolymer of the substrate; and a temperature-responsive, cholesteric LCP film chemisorbed to a surface of the copolymer substrate, wherein the LCP film has a broadband response at a relative humidity of 60% to 95%.

[0006] A method of forming the layered article as described above, the method comprising: providing a copolymer substrate having opposed first and second sides, and comprising a Type II photoinitiator covalently linked to the copolymer; applying a primer composition comprising 0.1 to 7 weight percent, preferably 0.1 to 2 weight percent of a Type II photoinitiator onto a first surface area of the first side of the copolymer substrate to form a primer layer; applying a coating composition comprising a liquid crystal monomer composition onto at least a portion of the primer layer under shear to provide an aligned coating layer;

irradiating the aligned coating layer on the second side of the copolymer substrate and through the substrate to form a liquid crystalline film on the substrate; and treating the liquid crystalline film with an aqueous base to form the layered article.

[0007] An article including the layered article is described. In particular, a window includes a frame; and a sheet supported by the frame, wherein the sheet comprises the layered article.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIG. 1 is side cross-sectional view illustrating a liquid crystalline coating on a polycarbonate copolymer substrate according to the present disclosure;

[0009] FIG. 2A is UV-Vis spectra of comparative example 1 at 75% RH and different temperatures;

[0010] FIG. 2B is a graph showing the area of the water peak and the shift of the reflection band versus temperature at a RH of 75% of comparative example 1;

[0011] FIG. 2C is a graph showing the shift of reflections bands versus temperature at various RH levels ranging from 30 to 75% of comparative Example 1;

[0012] FIG. 3 an SEM cross-section of an LCP coating of comparative example 2;

[0013] FIG. 4 is an SEM cross-section of an LCP coating of comparative example 3;

[0014] FIG. 5 is an SEM cross-section of an LCP coating of inventive example 4;

[0015] FIG. 6A is a transmission spectrum of the reflection band of example 4, before and after the alkaline treatment, including saturated (wet) and dried coatings after alkaline treatment;

[0016] FIG. 6B is a transmission spectrum of example 4 after alkaline treatment of the coating at various temperatures (constant RH of 75%);

[0017] FIG. 6C is a transmission spectrum of example 4 after alkaline treatment of the coatings at -2°C after cooling from 70°C at various time intervals.

DETAILED DESCRIPTION

[0018] The inventors hereof have discovered an improved layered article having a temperature- sensitive film chemisorbed to a copolymer substrate and having a temperature- dependent broadband response. The broadband response can be in the ultraviolet (UV), visible, or infrared (IR) region of the spectrum. The film is chemisorbed to a substrate by a method that allows the wider response range. In particular, use of a substrate having a Type II photoinitiator covalently linked to the substrate, together with a primer layer comprising a Type II

photoinitiator and a modified LC film-forming composition allows the formation of a pitch gradient within the LCP film as described in further detail below. The layered articles can be used to manufacture a self-regulating window.

[0019] The films and windows have a number of advantageous properties.

Responsiveness is high, in that the change from one state to the other begins within a few seconds, and is complete within minutes, e.g., in less than 30 minutes depending on temperature change and other factors. The LCP film has good mechanical properties. In another

advantageous feature, the response is autonomous, that is, it does not require user input. Another significant advantage is that no additional energy input is required for the film to function.

Deposition of the films can be a one-step process. Moreover, the film does not need to be sandwiched between two glass plates, which can provide a manufacturing and weight savings. Finally, the functionality of the films is optimum at atmospheric relative humidity (RH) levels of 60% to 95%. The films are therefore especially useful in controlled higher humidity

environments, such as in greenhouses.

[0020] The layered article includes a cholesteric LCP. The LCP is designed to have a pitch change, which induces a reflection band shift, and is triggered by water molecule intercalation. At lower temperatures, the films can absorb more water because water condenses more easily and therefore penetrates the films to a greater extent. Water absorption between the layers results in an increase in the helix pitches, leading to a red shift (towards longer

wavelenghts) of the reflection band. At higher temperatures, water is released, and the helix pitches decrease, which results in a blue shift (towards shorter wavelengths) of the reflection band. This shift can occur in the near IR region or other region of the spectrum. Advantageously, changing the wavelength of the reflection band can be achieved by changing the chiral dopant concentration. Thus, the polymers and other aspects of the layered article can be adjusted by changing the chiral dopant concentration to achieve shifts in other regions of the spectrum, for example in the UV-visible region.

[0021] The liquid crystals in the films described herein can be designed to have a pitch gradient within the film. In particular, cholesteric liquid crystals possess a helical structure, and organize in layers with no positional ordering within layers except for a director axis n, which varies with the layers, and tends to be periodic in nature. The period of this variation, i.e., the distance over which a full rotation of 360° is completed, defines the pitch of the helix. For cholesteric LCP films, periodic changes of the refractive index due to the orientation change of the liquid crystal orientation create the parallel planes needed to induce Bragg reflection.

Coatings with a pitch gradient can therefore reflect a broader wavelength range. A pitch gradient can be obtained by use of a primer layer having a photoinitiator, for example a Type II photoinitiator, but adhesion between the coating and the substrate may not be sufficient.

However, it has been found that use of a substrate having a Type II photoinitiator covalently linked to the substrate, together with a primer layer comprising a Type II photoinitiator, and a modified LC film-forming composition can provide both the desired pitch gradient for broadband response films, together with good adhesion.

[0022] The LCP film is covalently bound to a substrate as described in more detail below. The LCP films are a thermotropic, cholesteric LCP network that can be prepared by photopolymerizing liquid crystal (LC) monomers containing a polymerizable carbon-carbon double bond of formula (1):

RHC=CRX (1)

wherein each R is independently hydrogen or a substituted or unsubstituted C1-12 alkyl, and X is a group containing a liquid crystal moiety. In an aspect, the group X contains one reactive end group, referred to herein as a“bifunctional” LC monomer. In an aspect, X also contains at least one additional carbon-carbon double bond, which is referred to herein as a“polyfunctional” LC monomer.

[0023] In an aspect, R in formula (1) is hydrogen or methyl, and the liquid crystal moiety in group X is contains at least a thermotropic mesogenic moiety and a flexible spacer moiety between the mesogenic moiety and the polymerizable carbon-carbon double bond. In particular, the mesogen can comprise at least one or more aromatic groups. The identity of the spacer moiety and the rigid core can determine the type of phase of the LC monomer (e.g., nematic or smectic); the transition temperatures between e.g. the isotropic and nematic phase; and the flexibility of the LCP network, and thus indirectly the mechanical properties and switching time of the LCP.

[0024] In preferred aspects, the LC monomer is a (meth)acrylate LC monomer having a terminal (meth)acrylate group, i.e., a monomer of formula (2):

wherein Ri is hydrogen (an acrylate group) or methyl (a methacrylate group); and X is a group containing a liquid crystal moiety as described above.

[0025] In preferred aspects, the LC group X comprises at least one mesogenic moiety Y and at least one spacer moiety Z (and usually more than one such moiety). For example, such LC moieties can have the structure of formula (A):

«LLL Z - ULLL )

wherein each of Z and Y are independently bound to another mesogenic moiety Y, spacer moiety Z, a nonreactive end group, or a reactive end group such as a terminal (meth)acrylate group (2). The combination of the spacer Z and mesogenic Y moieties gives the LC monomers an elongated (i.e., rod-like) shape responsible for the liquid crystalline behavior of the films. Thus, a bifunctional monomer can have the general structure: reactive end group-spacer-LC moiety-non-reactive end group. A poly functional monomer can have the following general structure: first reactive end group-first spacer-LC moiety-second spacer-second reactive end group. In an aspect, each spacer moiety Z independently comprises the same or different C _1-30 aliphatic group, preferably a C _1-30 non-cyclic alkyl group.

[0026] In an aspect the mesogenic moiety Y of the LC group X comprises at least one aromatic group, which creates flat segments in the LC monomer. In an aspect, the mesogenic moiety Y can comprise one or more derivatives of /i-hydroxybenzoic acid, having the structure of formula (B):

wherein each R ² is the same or different, and is each independently an aromatic group, - C(=0)0-, -0-, -0C(=0)0-, a heterocyclic or fused heterocyclic ring system, or a single bond. In addition to the at least one aromatic group, the mesogenic moiety Y can further comprise one or more ester, ether, or carbonate linkages.

[0027] In another aspect the mesogenic moiety Y is a heterocyclic or fused heterocyclic ring system (i.e., a nonaromatic ring system without a delocalized pi system). The heterocyclic or fused heterocyclic ring system has at least one heteroatom, such as nitrogen, sulfur, selenium, silicon, oxygen, or a combination thereof. For example, a portion of the mesogen moiety Y of LC group X can comprise a moiety having the structure of formula (C):

wherein each R ³ is the same or different and is independently -C(=0)0- or an oxygen atom. In other aspects, the mesogen moiety Y can comprise a group having of formula (C) linked to a derivative p-hydroxybenzoic acid (B).

[0028] In an aspect the LC monomer can be a chiral LC monomer (a“chiral dopant”) having the general structure: first reactive end group- first spacer-first LC moiety-chiral element-second LC moiety-second spacer-second reactive end group. An exemplary chiral LC monomer having a chiral center derived from a group of formula (C) is the polyfunctional monomer of formula (3):

wherein the chirality is illustrated by the two bonds connecting the fused heterocyclic rings directed in the same direction out of the plane. Chirality can be altered by instead directing one of the bonds connecting the fused heterocyclic rings into the plane. It is further noted that the length of the spacer moieties, while illustrated as being 4 carbon atoms long, can be varied; and while terminal acrylate groups are shown, methacrylate groups can be used. Likewise, the derivatives of /i-hydroxybenzoic acid on either side of the fused heterocyclic rings can be altered.

[0029] The chirality can likewise be altered by adding a pendent group to the LC monomer wherein the pendant group has a chiral center. An example of a bifunctional, chiral LC monomer having a pendant chiral group has the structure of formula (4a):

wherein R ¹ is hydrogen or methyl and i is an integer 1 to 10. An exemplary monomer of this type has a structure of formula (4b): (4b).

[0030] Alternatively, the chiral LC monomers can be bifunctional, having a chiral group on the spacer moiety. An example is the bifunctional monomer having the structure of formula (5) (and its methacrylate analogue), and the monomer formula (6):

wherein each R is independently hydrogen or a substituted or unsubstituted C1-12 alkyl, and Y is a mesogenic moiety as defined formula (2). Other examples include the (meth)acrylate analogs of formula (6). The chain length of the spacer and the location of the chiral center can be varied and is not limited to the examples of formulas (4) and (5). Likewise, the chiral LC monomers can be polyfunctional monomers having a chiral center located on each of the spacer moieties.

[0031] In addition to or instead of the chiral LC monomers, chirality can be incorporated into the film by adding a chiral dopant, i.e., a chiral molecule that does not participate in polymerization. Non-limiting examples of chiral molecules include those of formulas (7), (8), and (9):

[0032] In further aspects, the LC monomer can comprise a polyfunctional monomer having at least two terminal (meth)acrylate groups. An example of such LC monomers includes bifunctional monomers having the structure of formula (10):

wherein each R ¹ is independently hydrogen or methyl, and X is an LC moiety as described above. In an aspect, the polyfunctional monomer having at least two terminal (meth)acrylate groups and can have a structure of the formula (lOa):

wherein each R ¹ is independently hydrogen or methyl and each spacer moiety Z and mesogenic moiety Y are as defined above. In an aspect, each spacer moiety Z is the same. Without being bound by theory, it is believed that the spacer moieties Z being the same can beneficially result in an improved crystalline nature of the LCP film, facilitating the crystalline stacking of the mesogenic moiety Y of neighboring LC monomers.

[0033] In another aspect, the polyfunctional monomer can have a structure of formula

(lOb):

wherein each R ¹ is independently hydrogen or methyl, each i is the same or different and is an integer of 1 to 10, and Y is a mesogenic moiety. In an aspect, i in both instances is the same integer. For example, the bifunctional monomer of the Formula (lOb) can be a bifunctional monomer of the formula (lOb-l): (lOb-l) wherein each R ¹ is independently hydrogen or methyl, R ⁴ is hydrogen, substituted or unsubstituted C1-12 alkyl, and each i is the same and is an integer of 1 to 10. For example, R ₄ can be a methyl group and i in both instances can be 3; R ⁴ can be a methyl group and i in both instances can be 6; R ⁴ can be hydrogen and i in both instances can be 6; R ⁴ can be hydrogen and i in both instances can be 3; R ⁴ can be a hexyl group and i in both instances can be 6. Again, the length of the R ⁴ group can be adjusted to tune the properties of the LCP film, for example, resulting in an increase or decrease in the transition temperature between the nematic and isotropic phases. Specific LC monomers of this type include the monomers having the structure of formula ( (lOb-2) (l0b-3).

Still other specific LC monomers of this type include ((4,4’-((((oxybis(ethane-2, l- diyl))bis(oxy))bis(ethane-2, l-diyl))bis(oxy)bis(benzoyl)) bis(oxy))bis(4,l-phenylene)bis(4-((6- (acryloyloxy)hexyl)oxy)-2-methylbenzoate) of formula (lOb-4):

l,4-phenylene bis(4-((6-acryloyloxy)-3-methylhexyl)oxy)benzoate) of formula (l0b-5)

or 2-methyl- l,4-phenylene bis(4-((6-(acryloyloxy)hexyl)oxy)benzoate) of Formula (lOb-6)

(lOb-6).

[0034] The poly functional monomer can be a light-responsive monomer. In an aspect, the polyfunctional, light-responsive monomer can have the structure of Formula (lOb-7), where the mesogenic moiety Y comprises an azo group. For example, the polyfunctional, light- responsive monomer can have the structure of formula (lOb-7):

(lOb-7)

wherein each R ¹ is independently hydrogen or methyl, and each i is the same and is an integer of 1 to 10. In an aspect R ¹ is methyl and i is 3.

[0035] In other aspects, the LC monomer can have at least one terminal nitrile group (- CN) and at least one other terminal group, or at least one terminal ether group and at least one other terminal group. Exemplary ether groups include C1-12 alkyl ethers, for example methoxy or octyloxy. Exemplary monomers of this type have structures of formula (11), (12), or (13) (4- methoxyphenyl 4-((6-(acryloyloxy)hexyl)oxy)benzoate) .

[0036] In still other aspects, the LC monomer can have at least one terminal carboxy group. Exemplary monomers of this type have structures of formula (14) and (15):

[0037] Although the structures of formula (14) and formula (15) themselves individually are not LC monomers, two of the molecules together can form hydrogen bonds via their carboxylic acid groups and the resultant structure forms the LC monomer.

[0038] The LC monomers are present in a coating composition used to form the LCP film as described in further detail below. Although the coating composition can contain a single LC monomer, a plurality of LC monomers is preferably used. The relative types, amounts, and ratios of LC monomers in the coating composition is adjusted to tune properties of the LCP polymer or coating composition, such as the nematic-isotropic phase transition temperature (T _NI ), the degree of cross-linking in the LCP film, the viscosity of the coating composition or film, response to specific stimuli, or the helix pitch of the cholesteric liquid crystalline polymer. For example, chiral dopants, such as the monomer of formula (3) can be used to obtain cholesteric LCP films. It has been found by the inventors hereof that in an aspect, use of bifunctional chiral dopants (as opposed to polyfunctional chiral dopants) can contribute to providing a gradient, which contributes to the broadband response. Polyfunctional monomers of formulas (lOb-2), (l0b-3), (lOb-4), (l0b-5), or (lOb-6) can be used to obtain a specific degree of cross-linking. Monomers such as those of formula (3), (4a), (14), or (15) can be used to tune the TNI of the films.

[0039] In some specific aspects, the coating composition can comprise 1 to 5 wt% of a bifunctional chiral dopant, such as an LC monomer of formulas (4a), (4b), (5), or (6); 10 to 30 wt% of a polyfunctional LC monomer of formulas (lOb-2), (l0b-3), (lOb-4), (l0b-5), or (lOb-6); 20 to 40 wt% of bifunctional LC monomers of formulas (11), (12), (13), or a combination thereof; and 30 to 50 wt% of the carboxylic acid-containing bifunctional LC monomers, such as monomers of formulas (14) and (15). All of the foregoing amounts based on the total weight of the LC monomers.

[0040] In an aspect, the coating composition further comprises a Type II photoinitiator, which can be different from or the same as the Type II photoinitiator used in the

copolycarbonate and the primer layer. The type and amount of Type II photoinitiator is selected based on the type of LC monomers used, the irradiation parameters used, the desired degree of crosslinking, and like considerations. In an aspect, the Type II photoinitiator is a benzophenone, a thioxanthone, a xanthone, or a quinone.

[0041] Benzophenones have the general structure of formula (i):

wherein each W is independently C1 -12 alkyl, carboxyl, hydroxyl, or amino; and m and n are each independently integers from 0 to 2. Exemplary benzophenone Type II photoinitiators include benzophenone (m=n=0); 3,3',4,4'-benzophenonetetracarboxylic dianhydride (m=n=2); 4,4'-bis(diethylamino)benzophenone; 4,4'-bis(dimethylamino)benzophenone; 4,4'- dihydroxybenzophenone; 4-(dimethylamino)benzophenone; 2,5-dimethylbenzophenone (m=0, n=2); 3,4-dimethylbenzophenone (m=0, n=2); 3-hydroxybenzophenone (m=0, n=l); 4- hydroxybenzophenone; 2-methylbenzophenone; and 3-methylbenzophenone.

[0042] Thioxanthones and xanthones are compounds that contain a structure of formula

(ii):

wherein X is sulfur or oxygen. The thioxanthone or xanthone can have substituents such as C1 -12 alkyl; halogen; or C1-12 alkoxy. Exemplary thioxanthone Type II photoinitiators include thioxanthone; l-chloro-4-propoxythioxanthone; 2-chlorothioxanthone; 2,4- diethylthioxanthone; 2-isopropylthioxanthone; 4-isopropylthioxanthone; and 2- mercaptothioxanthone.

[0043] Quinones generally have a fully conjugated cyclic dione structure. Exemplary quinone Type II photoinitiators include anthraquinone; anthraquinone-2-sulfonic acid;

camphorquinone; 2-ethylanthraquinone; and phenanthrenequinone.

[0044] In an aspect, the coating composition can comprise 1 to 5 wt% of the type II photoinitiator, based on the total weight of solids.

[0045] The coating compositions can accordingly comprise 90 to 100 wt%, or 90 to 100 wt% of LC monomers (by solids), and when present, 1 to 10 wt% of a second photoinitiator by solids). Other components of the coating composition can be additives known in the art, for example 0.5 to 5 wt% of a surfactant (by solids). An exemplary surfactant is 2-(N- ethylperfluorooctanesulfonamido) ethyl methacrylate.

[0046] In conventional methods, the LC monomer composition is polymerized directly on a surface of a substrate. The reaction takes place in the presence of a Type I photoinitiator that, under ultraviolet (UV) light, undergoes a homolytic bond cleavage, resulting in radicals that induce polymerization of the carbon-carbon double bond. In these processes, the surface of the substrate does not take part in the polymerization, yielding a physisorbed film. However, such LCP films are often plagued by delamination (peeling), i.e., the premature detachment of the film from the substrate. The accompanying loss of function reduces the lifespan of an article containing the film. This is particularly so for polymeric substrates.

[0047] Use of a primer layer containing a Type II photoinitiator can provide

chemisorption between the film and a surface of a polymer substrate. Thus, a primer layer is present between the substrate and the LCP coating compositions when forming the LCP film, or more precisely, diffused into outer layers of the polymer substrate. The primer layer is formed from a primer solution, which can be formed by dissolving an amount of the Type II photoinitiator as described above in a solvent. Preferably the solvent dissolves the Type II photoinitiator but does not degrade the substrate. In an aspect, the solvent an alcohol, such as methanol, ethanol, n-propanol, or i-propanol; or an alkane, such as hexane can be used. It has been found by the inventors hereof that use of a relatively lower amount of the Type II photoinitiator contributes to formation of the gradient in the LCP film, i.e., an amount lower than 10 wt% of the priming solution. In an aspect, the priming solution comprises 0.1 to 7 wt%, or 1 to 5 wt% of the Type II photoinitiator, based on the total weight of the priming solution.

[0048] However, it has been found that under certain circumstances the chemisorption is not robust, for example the coating delaminates during base treatment as described below. This disadvantage is overcome in part by use of a copolymer substrate that includes a Type II photoinitiator chemically bound to the copolymer substrate. It has been found that use of a copolymer substrate that includes a copolycarbonate having benzophenone moieties chemically linked (covalently linked) to the polymer chain provides improved adhesion of the film, while simultaneously allowing the manufacture of broadband response films. Without being bound by theory, it is believed that during manufacture of the films, benzophenone deposited onto a bisphenol A homopolycarbonate substrate as a primer layer diffuses into the film, and that limited solvent swelling of the copolymer substrate surface promotes intermingling of the polymer chains, such that use of the primer layer and the copolymer substrate having a Type II photoinitiator provides both a sufficient density of chemical bonds between the coating and the substrate and also entanglement of the polymer chains. Thus, when a copolymer substrate containing chemically-linked benzophenone moieties is used, at least a portion of the benzophenone in the primer layer can still diffuse through the monomer mixture during coating preparation to enable coating curing and cholesteric LC pitch gradient formation. However, another portion of the benzophenone in the primer layer and the chemically linked

benzophenone groups of the copolymer backbone remain, and provide a higher benzophenone density at the coating-substrate interface as well as entanglement, which is believed to improve adhesion.

[0049] The photoinitiator can be covalently linked to the copolymer as a polymer unit, i.e., as unit of a graft, or as a unit of the polymer main chain. The type II photoinitiator can be incorporated into the copolymer by co-reaction of the type II photoinitiator (or a derivative thereof) during synthesis of the copolymer, or by grafting. The other units of the copolymer are selected to have abstractable hydrogen atoms and to provide the desired substrate properties, such a flexibility, hardness, mechanical strength, and the like. The other copolymer units are further selected to be sufficiently transmissive of the activating radiation to allow manufacture of the films as described in further detail below. For example, the other copolymer units can be selected to provide a substrate having one or more of a transparency of 80% or greater, as determined according to ASTM standard D- 1003 -00); a Young’s modulus of 1 GigaPascal (GPa) or greater, or 2 GPa or greater, each as determined according to ASTM D 882 (2012).

[0050] Other copolymer units that can be used include carbonate units, ester units, siloxane units, (meth)acrylate units and the like, or a combination thereof, for example a combination for carbonate and ester units, or a combination of carbonate units and siloxane (e.g., dimethylsiloxane) units. Methods for the manufacture of copolycarbonates, copolyesters, copoly(carbonate-ester)s, and the like are known in the art.

[0051] A preferred copolymer for use as the copolymer substrate is a copolycarbonate, i.e., a polycarbonate copolymer comprising a Type II photoinitiator chemically bound to a polycarbonate main chain as a polymer unit. The copolycarbonate comprises repeat structural carbonate units of formula (20)

o

- R ¹ — o— c— o - (20)

wherein at least 60 percent of the total number of R ¹ groups are aromatic, or each R ¹ contains at least one C ₆ -3o aromatic group. Specifically, each R ¹ can be derived from a dihydroxy compound such as an aromatic dihydroxy compound of formula (21) or a bisphenol of formula (22).

In formula (21), each R ^h is independently a halogen atom, for example bromine, a Ci-io hydrocarbyl group such as a Ci-io alkyl, a halogen-substituted Ci-io alkyl, a C ₆ -io aryl, or a halogen-substituted C ₆ -io aryl, and n is 0 to 4.

[0052] In formula (22), R ^a and R ^b are each independently a halogen, C1-12 alkoxy, or Ci- 12 alkyl, and p and q are each independently integers of 0 to 4, such that when p or q is less than 4, the valence of each carbon of the ring is filled by hydrogen. In an aspect, p and q is each 0, or p and q is each 1, and R ^a and R ^b are each a C1-3 alkyl group, specifically methyl, disposed meta to the hydroxy group on each arylene group. X ^a is a bridging group connecting the two hydroxy- substituted aromatic groups, where the bridging group and the hydroxy substituent of each C ₆ arylene group are disposed ortho, meta, or para (specifically para) to each other on the C ₆ arylene group, for example, a single bond, -O-, -S-, -S(O)-, -S(0) ₂ -, -C(O)-, or a Ci-is organic group, which can be cyclic or acyclic, aromatic or non-aromatic, and can further comprise heteroatoms such as halogens, oxygen, nitrogen, sulfur, silicon, or phosphorous. For example,

X ^a can be a substituted or unsubstituted C3-18 cycloalkylidene; a C1-25 alkylidene of the formula - C(R ^c )(R ^d ) - wherein R ^c and R ^d are each independently hydrogen, C1-12 alkyl, C1 -12 cycloalkyl, C7-12 arylalkyl, C1 -12 heteroalkyl, or cyclic C7-12 heteroarylalkyl; or a group of the formula - C(=R ^e )- wherein R ^e is a divalent Ci -12 hydrocarbon group. Some illustrative examples of dihydroxy compounds that can be used are described, for example, in WO 2013/175448 Al, US 2014/0295363, and WO 2014/072923. Specific dihydroxy compounds include resorcinol, 2,2- bis(4-hydroxyphenyl) propane (“bisphenol A” or“BP A”), 3,3-bis(4-hydroxyphenyl)

phthalimidine, 2 -phenyl-3, 3’ -bis(4-hydroxyphenyl) phthalimidine (also known as N-phenyl phenolphthalein bisphenol,“PPPBP”, or 3,3-bis(4-hydroxyphenyl)-2-phenylisoindolin-l-one),

1 , 1 -bis(4-hydroxy-3 -methylphenyl)cyclohexane, and 1 , 1 -bis(4-hy droxyphenyl)-3 ,3,5- trimethylcyclohexane (isophorone bisphenol).

[0053] The copolycarbonates further comprise repeat structural carbonate units of formula (23) o

- R ² — o— c— o - (23)

wherein R ² is not the same as R ¹ , and R ² is a type II photoinitiator moiety as described above. The type II photoinitiator can be incorporated into the polycarbonate by co-reaction of its mono- or di-sub stituted hydroxy derivative during synthesis of the polycarbonate, as described, for example, in WO 2015/193862. A specific photoinitiator is a benzophenone. Mono- and dihydroxybenzophenones are known, for example 4-hydroxybenzophenone and 4,4’- dihydroxybenzophenone. When a monohydroxy benzophenone is used, the benzophenone can be incorporated into the polycarbonate as a terminal group, in an amount, for example, of 0.5 to 15 mole percent (mol%). When a dihydroxy benzophenone is used, the benzophenone can be incorporated into the polycarbonate as a backbone unit, in an amount, for example, of 0.5 to 50 mol%.

[0054]0ther type II photoinitiator moieties can be derived from a 9H~thioxanthen~9~one or 9-xanthone of the formulas

or an isomer thereof ^’ wherein each Q is independently the same or different, and is a group reactive with the comonomer, for example a hydroxy, carboxylic acid (~C(=O)0H), carboxylic acid salt, (C _1-3 alkyl) carboxylic ester; haloforraate such as chloroforrnate, or the like, wherein the reactive group can be linked directly to a carbon ring atom, or be linked to the ring system by a tether, such as a (Cm alkylene) ether. An example of the reactive group being linked by a tether is the group -0~CH2-C00H. Isomers can include structures wherein one or more of the Q are present on a different carbon atom of the ring system.

[0055] The copolycarbonate can be used by itself as the copolymer substrate, with optional additives as known in the art, for example a dye, mold release agent, heat stabilizer, ultraviolet light stabilizer, or the like, or a combination thereof. In an aspect an additional polymer compatible with the copolycarbonate is present. For example, another polycarbonate such as a homopolycarbonate can be present e.g., a bisphenol A homopolycarbonate. If an additional polymer is used, it can be present in an amount of 1 to 50 wt%, for example.

[0056] The copolymer substrate can be in the form of a molded article, a sheet, or a film. The substrate can be formed by a variety of known processes, such as casting, profile extrusion, film or sheet extrusion, sheet-foam extrusion, injection molding, blow molding, thermoforming, and the like. The substrate itself can be a component of an article, such that the article comprises a substrate to be coated with an LCP film.

[0057] In the process of forming the LCP film on a substrate, a coating composition comprising the LC monomers is applied to the substrate to form a coating layer, and the coating layer is irradiated to photograft the monomers to form a film. Photografting includes

polymerization of the monomers and grafting of the polymers to the substrate via a covalent bond. Thus, when the coating layer is exposed to the appropriate wavelength and intensity of light, the Type II photoinitiator produces radicals that induce a reaction with the surface of the substrate and with the LC monomers, forming a liquid crystalline polymer matrix that is chemically attached to the substrate. The LC coating layers are thereby covalently bound (i.e., chemisorbed) to the surface of the substrate, and exhibit improved adhesion properties.

Optionally, the process can further comprise forming a primer layer comprising a Type II photoinitiator directly to the substrate; followed by applying the coating composition directly onto the primer layer with no other intervening layers.

[0058] In particular, a coating composition is applied to an area of a first surface of the copolymer substrate. Generally, the copolymer substrate can have at least a first surface and a second surface opposite the first surface, although the substrate can be provided in a variety of regular or irregular shapes and sizes. As described above, the coating composition comprises at least one LC monomer, and optionally a Type II photoinitiator. The Type II photoinitiator in the coating composition is generally the same as the Type II photoinitiator in the copolymer substrate. The coating composition can be applied to one or more different surfaces of the substrate, or to only a portion of a surface of the substrate, depending on the desired area to be grafted with the LCP. The coating composition can be applied directly to the substrate, with no intervening layers in between. In an aspect, the coating composition can be applied while at room temperature, or at ambient pressure, or in open air, preferably all three. Generally, however, the coating composition is applied at a temperature that is lower than the nematic- isotropic phase transition temperature (TNI) of the coating composition and higher than the crystal-nematic phase transition temperature (TCN).

[0059] When the optional primer layer is used, the primer solution as described above is applied to an area of the substrate before the coating composition to form a primer solution layer. The primer solution is preferably applied to the same area as where the coating

composition is to be applied. The primer solution comprises a Type II photoinitiator in a solvent. The coating composition can be directly applied, or in an aspect the primer solution layer can be maintained on the surface of the substrate for a period of time to allow the solvent to partially or fully evaporate to form a primer layer, before applying any other layers. Depending on the solvent, this period of time may be 10 seconds to 1 hour or more, preferably 30 seconds to 30 minutes. Evaporation of the solvent can proceed at ambient conditions or with application of heat, for example in an oven. The primer layer can be applied to one or more different surfaces of the substrate, or to only a portion of a surface of the substrate, depending on the desired area to be grafted with the LC coating composition. Advantageously, the primer layer can be applied directly to the substrate, with no intervening layers in between. In an aspect, the primer layer can be applied while at room temperature, or at ambient pressure, or in open air, preferably all three.

[0060] Preferably, the coating layer (or, if present, the primer layer) directly contacts the surface of the copolymer substrate. If a primer layer is present, preferably the coating layer is applied directly on the primer layer with no intervening layers. Further, the methods described herein can be performed without pre-activating the surface of the substrate, treating the surface of the substrate with other substances prior to applying the primer layer or the coating layer (e.g. plasma treatment, or acid/base application, or coating with a thin layer of a hydrogen-rich material like polydopamine or polyphenols); or post-polymerization purification steps. In particular, the coating layer (or, if present, the primer layer) is applied without pre-treatment for LC alignment or without use of an alignment layer. Alignment layers are commonly used in the industry, and include, for example, applying a polyimide (PI) layer to the substrate, which is subsequently rubbed with a soft fabric to scratch the PI layer, and subsequently applying the liquid crystalline composition to the PI layer. The scratches act as a template for orientation of the liquid crystalline polymers in a particular direction. Rather than an alignment layer, the LC orientation of the coating layer can be induced by shear during their deposition upon the substrate (e.g. with a doctor blade, using a slot die, or other spreading mechanism, or by printing).

[0061] Next, the coating layer and the primer layer are irradiated through the substrate to form an LCP film. The layers can be irradiated by exposure to ultraviolet (UV) light at an appropriate wavelength and in an appropriate dosage that brings about the desired amount of photopolymerization and crosslinking of the LC monomers for the given application. The irradiation should reach the substrate-primer-coating interface, permitting the photoinitiator to cause the formation of covalent bonds between the substrate and the LCPs formed during the irradiation. To obtain a pitch gradient, the coating layer and the primer layer are not directly exposed to UV light. Rather, the substrate is transmissive or transparent to UV radiation, and a second surface of the substrate is exposed to the UV light, so that the coating layers are irradiated by UV light transmitted through the substrate. The light transmitted through the substrate causes the photoinitiator in the copolycarbonate layer, the primer layer, and the coating layer to initiate polymerization of the LC monomers. The polymer of the substrate is accordingly selected to be sufficiently transmissive to UV irradiation to allow initiation and photopolymerization at the selected dose and time of exposure. For example, a sample of the substrate having a thickness of 1 millimeter can transmit at least 50%, or at least 70%, or at least 90% of radiation in the UV range at a selected intensity.

[0062] In an aspect, the irradiation of the coated substrate is performed under a continuous nitrogen flow. The level of irradiation and the exposure time of the coating layer to the photoactivating radiation depends on the LC monomers and photoinitiators used, the intended application, and the particular properties of the substrate (e.g. % UV transmittance). It has been found that lower levels of irradiation and longer times allow the formation of the pitch gradients. In aspects, the coating layer can be irradiated for 1 minute to 1 hour, or 2 to 20 minutes, depending on the irradiation system.

[0063] The irradiation can be accomplished by using a UV-emitting light source such as a mercury vapor, High-Intensity Discharge (HID), or various UV lamps, such as commercial UV lamps sold for UV curing from manufacturers such as Excelitas Technologies (for example, the OMNICURE™ LX500 UVLED curing system), Heraeus Noblelight, and Fusion UV. Non limiting examples of UV-emitting light bulbs include mercury bulbs (H bulbs), or metal halide doped mercury bulbs (D bulbs, H+ bulbs, and V bulbs). Other combinations of metal halides to create a UV light source are also contemplated. Exemplary bulbs could also be produced by assembling the lamp out of UV-absorbing materials and considered as a filtered UV source. An H bulb has strong output in the range of 200 nanometers (nm) to 320 nm. The D bulb has strong output in the 320 nm to 400 nm range. The V bulb has strong output in the 400 to 420 nm range.

[0064] It can be advantageous to use a UV light source where wavelengths that can cause polymer degradation or excessive yellowing are removed or are not present. Equipment suppliers such as Excelitas, Heraeus Noblelight, and Fusion UV provide lamps with various spectral distributions. The light can also be filtered to remove unwanted wavelengths of light, for example with optical filters that are used to selectively transmit or reject a wavelength or range of wavelengths. These filters are commercially available from a variety of companies such as Edmund Optics or Praezisions Glas & Optik GmbH. Bandpass filters are designed to transmit a portion of the spectrum, while rejecting all other wavelengths. Longpass edge filters are designed to transmit wavelengths greater than the cut-on wavelength of the filter. Shortpass edge filters are used to transmit wavelengths shorter than the cut-off wavelength of the filter. Various types of materials, such as borosilicate glass, can be used as a long pass filter. Schott or

Praezisions Glas & Optik GmbH for example have the following long pass filters: WG225, WG280, WG295, WG305, WG320, which have cut-on wavelengths of 225, 280, 295, 305, and 320 nm, respectively. These filters can be used to screen out the harmful short wavelengths while transmitting the appropriate wavelengths for the crosslinking reaction. An exemplary lamp is a high pressure 200-watt mercury vapor short arc used in combination with a light guide. A filter and an adjustable spot collimating adapter (for spreading the light beam over a large surface) can also be used. Of course, protective equipment to protect the user can also be used.

[0065] In an aspect, the coating layer is exposed to light that includes UVA light wavelengths with an intensity of 0.5 to 10 milliwatts per centimeter squared (mW/cm ² ), or 1 to 5 mW/cm ² . UVA refers to wavelengths from 320 to 390 nm. This irradiation can be accomplished using a Collimated EXFO OMNICURE™ S2000 lamp.

[0066] After formation of the LCP film on the substrate, the carboxylic acid groups of the LCP film are converted to the salt form. For example, the layered article can be washed or soaked in an aqueous base solution such as sodium hydroxide or potassium hydroxide.

[0067] The resulting LCP films can have a broad reflection bandwidth, i.e., a broad reflection band, also referred to as a broadband reflective response, or simply a broadband response. As used herein, a“broad reflection bandwidth” or“broadband response” is all bands wider than Dl _kίΐ as determined by Eq. 1 :

Dl _GeA = (ne-no) * P (Eq. 1)

wherein

Dl _kA is the bandwidth,

ne is the extraordinary refractive index;

no is the ordinary refractive index; and

P is the pitch of the cholesteric alignment.

The value of (ne-no) can be determined by methods known in the art. For example, a tilting compensator can be used in a polarizing microscope, such as a“Tilting Compensator K” from Leitz Wetzlare. In an aspect, a broadband response is a band wider than the corresponding narrow band according to Eq. 1 above wherein P is the smallest pitch. In an aspect a broadband response can be obtained from diffusion of the benzophenone.

[0068] In an aspect the broadband response is located within a region of the spectrum from 10 nm (UV) to 1 millimeter (IR). For example, the broadband response can be located in the IR region of the light spectrum, for example in the region from 700 nm to 1 millimeter, or in the region of the spectrum from 800 to 1200 nm. Alternatively, the broadband response can be located in the UV-visible light region of the spectrum, for example in the region from 10 nm to 700 nm. Of course, the broadband response can also be located in overlapping regions of the spectrum, for example in a region that overlaps the visible and IR range, for example 600 to 1200 nm. The location of the response can be adjusted by adjusting the characteristics of the LCP film as is known in the art, for example by modifying the concentration of a chiral dopant. [0069] The particular shift of the broadband response (the magnitude of the shift in response to a temperature change) is selected based on the desired application of the LCP films, for example in a window. In an aspect the LCP films can have a broadband response shift (a shift along the spectrum) of 50 to 600 nm, or 50 to 400 nm, or 100 to 600 nm, or 100 to 400 nm, or 200 to 400 nm. The response can be measured, for example, using a full width at half maximum (FWHM).

[0070] The resulting LCP films can have an isotropic to nematic phase transition temperature of, for example, 60 to l00°C, such as 70 to 90°C. In an isotropic phase (i.e., liquid phase), the LCP film has no orientational order. However, in further aspects, the LCP film can maintain a nematic phase at room temperature. In the nematic phase, the LCPs can exhibit long- range orientational order (i.e., the long axes of the LC monomers tend to align along a preferred direction), although the locally preferred direction can vary throughout the LCP film.

[0071] The temperature range over which the films can show a response can be varied.

A suitable range is from -15 to 70°C, or from -10 to 70°C, from 0 to 70°C or from 2 to 70°C.

[0072] The resulting LCP film can have a thickness of 1 to 100 micrometers (pm), or 5 to 80 pm, or 10 to 50 pm, or 25 to 35 pm, although other thicknesses can be made.

[0073] In an aspect, the LCP films can have a broadband response shift of 50 to 600 nm, or 50 to 400 nm, or 100 to 600 nm, or 100 to 400 nm, or 200 to 400 nm at a relative humidity of 60% to 95%, over a temperature range of 2°C to 70°C. In another aspect the LCP films can have a broadband response shift of 100 to 400 nm, or 200 to 400 nm at a relative humidity of 60% to 90%, over a temperature range of 2°C to 70°C.

[0074] The LCP film can be formed from more than one layer. This can be done by sequentially applying another primer layer to a first LCP film layer to abstract hydrogen atoms from the first liquid crystalline layer. After the solvent has evaporated, a second coating layer is applied, and then irradiated to form a second LCP film crystalline layer. In this way, multiple liquid crystalline layers can be built up.

[0075] This disclosure also relates to a layered article comprising a substrate and an LCP film disposed on the substrate, where the film is made using the methods described herein. As would be understood by one of ordinary skill in the art, the primer layer as described herein (a combination of a solvent and a Type II photoinitiator) would not be present as a physical layer in the article after cure. At most, only a residue of the primer layer (e.g., residual solvent molecules, unreacted photoinitiator, photoinitiator products, or a combination thereof would be present in the layered article. In an aspect, the LCP film is disposed directly on the substrate, such that they are in contact and no intervening layers (except any residue of the primer layer) are present between the substrate and the LCP film. In this aspect, no additional layers of any type (i.e., additional to the substrate, any residue of the primer layer, and the LCP film) are present. In particular, no alignment layer is present between the substrate and the LCP film. Elimination of an alignment layer saves time and cost during manufacture of the layered articles.

[0076] Other additional layers can be present in the layered article, provided that they are not located between the substrate layer and the LCP film. For example, an additional layer can be disposed on a side of the substrate layer opposite the LCP film, or an additional layer can be disposed on a side of the LCP film opposite the substrate. For example, a protective or abrasion-resistant layer can be disposed on the LCP film, an adhesive layer can be disposed on the substrate, or both. Any combination of the additional layers can be present to provide the desired functionality. The multilayer films can be used disposed on a glass plate or between glass plates. However, in an advantageous aspect, the multilayer article is not sandwiched between two glass plates, which can provide a manufacturing and weight savings.

[0077] These articles can be useful in applications such as windows, infrared reflectors, haptics, sensors, including biosensors, photochromies, displays, data storage, anticounterfeiting applications, security applications, optical films, robotics (e.g., controlling friction of the surface), and microfluidics. The window can be for a vehicle, such as a car, truck, boat, or ship, or for a building of any type, and can be used with or without a frame or other window component. The windows are especially useful for buildings such greenhouses.

[0078] The invention is further illustrated by the following non-limiting examples.

EXAMPLES

Materials

[0079] The materials used in the Examples are described in Table 1.

Table 1.

Characterization

[0080] Ultraviolet- visible light (UV-VIS) measurements were performed on a Perkin Elmer Lambda 750 UV-VIS-NIR spectrophotometer equipped with a 150 mm integrating sphere containing a lead sulfide (PbS) and photomultiplier tube (PMT) detector. All temperature dependent UV-Vis experiments were performed in a Shimadzu UV-Vis spectrophotometer in transmission mode. Unless stated otherwise, all measurements are corrected for polycarbonate as a reference. For the humidity and temperature experiments, a closed compartment for humidity control and a Linkam heating stage to change the temperature was used.

[0081] Scanning electron microscope (SEM) images was obtained from a Fei Quanta 3D-FEG. The measurement parameters were as follows: acceleration voltage: 5 kilovolts, working distance: 10 mm, and high vacuum.

Example 1. Narrowband films.

[0082] This example describes the preparation and properties of a narrowband, temperature-responsive film on a PC substrate using a 10% benzophenone primer layer.

[0083] A general procedure for preparation of the LC films on a polycarbonate (PC) substrate is as follows. To prepare the coating solution, an LC mixture was heated to its isotropic state and stirred for several minutes. Next, the LC mixture was applied to the substrate and heated again until the mixture was in its isotropic state (to ensure homogeneity) and then cooled to the cholesteric phase. This heating step can optionally be omitted. The coating was applied with a gap applicator having a gap height of 15 pm at 20°C. The coating was photopolymerized by exposure for 300 seconds to an unfiltered spectrum of a collimated EXFO OMNICURE S2000 lamp with an intensity of 30 mW/cm ² in the range 320-390 nm. This resulted in a fully polymerized film. In order to make the film water responsive, the fully polymerized film was treated with a 1M potassium hydroxide solution for approximately 7 minutes. Afterwards, the film was washed with water and dried at 60°C for 10 minutes.

[0084] The coating composition for Example 1 is shown in Table 2.

Table 2.

[0085] PC substrates (5x5 cm ² ) were treated at 40°C with 0.25 ml of a benzophenone - ethanol solution containing 10 wt% benzophenone. The ethanol solvent was allowed to evaporate for 15 minutes at 40°C on a heating plate, to provide substrates for coating with liquid crystal compositions. The coating composition was applied to the pre-treated PC plate as described above. After coating, polymerization, and subsequent base treatment, the film was fully wetted with water. After the base treatment, the coating does not delaminate from the substrate.

[0086] Temperature responsiveness of the layered article was investigated at 75% RH at different temperatures. As seen in FIG. 2A, the film shows a red shift of the reflection band upon cooling. At temperatures below 40°C the coating absorbed water and therefore shifted to higher wavelengths. At temperatures above 40°C almost no shift of the reflection band was observed. At approximately 5°C the coating did not absorb more water and therefore the maximum shift of the reflection band was approximately 211 nm which was less than the maximum shift when the coating was fully wetted. This can be explained by when the coating is fully wetted with water, water lays on top of the coating. This water is most likely absorbed easier by the coating than when the water has to penetrate from the air into the coating which leads to less water absorption and therefore a smaller shift.

[0087] The area of the water peak at 1950 nm in the transmission spectra was compared to the shift of the reflection band, as shown in FIG. 2B. The similarity of the curves in FIG. 2B indicates that the responsive behavior is mainly due to the absorption of water into the coating at different temperatures. The curves deviate only at lower temperatures. It is believed that this phenomenon is due to the formation of a water layer on top of the coating.

[0088] Temperature responsiveness was also investigated at 30%, 45%, and 60% RH. FIG. 2C shows that above 60% RH, a proper temperature response is present. The maximum shift of the reflection band increases with increasing RH.

Examples 2, 3, and 4. Broadband films

[0089] These examples describe the preparation and properties of broadband, temperature-responsive films on different polycarbonate substrates. In contrast to Example 1, the broadband films are formed by removing the photoinitiator from the film-forming coating composition and slightly altering the composition components and the initial curing intensity.

[0090] In the general procedure for broadband, temperature-responsive film formation, the substrate (10 x 7 cm ² ) was treated at 40°C with approximately 1 ml of a solution of benzophenone and ethanol. The ethanol was allowed to evaporate for 15 minutes at 40°C. After the pre-treatment the liquid crystal composition shown in Table 3 was coated onto the substrate. Before the coating was applied, the liquid crystal composition was heated to its isotropic state and stirred for several minutes. Next, the heated composition was applied onto the substrate with a bar coat with a gap height of 60 pm at 70°C. The coating was cured through the substrate at 70°C for 15-20 minutes using ETV light with an intensity of 3 mW/cm ² in the range 320-390 nm, followed by a 5 minutes post-cure through the substrate at 70°C using ETV-light with an intensity of 30 mW/cm ² in the range 320 to 390 nm.

Table 3.

[0091] In order to make the films water responsive, the fully polymerized films were treated with a 1 molar (M) potassium hydroxide solution for approximately 30 minutes.

Afterwards, the film was washed with water and dried at 60°C for approximately 10 minutes.

Example 2.

[0092] The above procedure was followed, using a PC substrate and a high concentration primer (10 wt% benzophenone in 90 wt% ethanol).

[0093] FIG. 3 is an SEM cross-sectional image of the LCP film thus prepared. The PC layer was removed during sample preparation, indicating poor adhesion to the substrate. At the bottom of the image (the surface formerly in contact the PC substrate), a severely distorted LCP region with inconsistent thickness can be seen. Additionally, crystals have formed at the surface of the coating cholesteric lines are visible and only in the middle of the film. These features show overall a poor alignment throughout the sample, leading to severe scattering.

Example 3.

[0094] The general procedures above were followed, using a PC substrate and a benzophenone-ethanol solution containing 0.5 wt% benzophenone.

[0095] Poor adhesion the LCP film and the PC substrate was observed. The resultant film is shown in FIG. 4. Better alignment is shown in this film, due to the lower concentration of benzophenone in the primer layer. At the bottom of the image (which is the portion of the LCP film previously in contact with the PC substrate) is a distorted region of the LCP film where no cholesteric lines are visible. In this region no LC alignment is present, which leads to some light scattering, and therefore haze. On top of this distorted zone, well-aligned cholesteric lines with few defects are seen. These layers reflect light of a certain wavelength and cause the reflection band.

Example 4

[0096] This example describes the preparation and properties of a broadband, temperature-responsive film on a copolycarbonate (BPA-DHBP) substrate using a 0.5 wt% benzophenone primer solution. The procedure described above was followed.

[0097] Adhesion between the LCP film and the BPA-DHBP substrate is significantly improved. FIG. 5 is an SEM cross-sectional image of the LCP film of Example 4. In this image, the PC substrate is still attached to the coating (bottom of image). The cholesteric pitch gradient can be very well seen. As with the other examples, an intermediate LCP region in which the LC are not aligned can be seen between the functional LCP film and the copolymer substrate. This region can lead to haze.

[0098] The temperature response of Ex. 4 was investigated at 75% RH. As can be seen in FIG. 6A and FIG. 6B, the broad reflection band redshifts upon cooling. FIG. 6C shows the cooling behavior when the LCP film is cooled rapidly from 70°C to -2°C, and then kept at -2°C for the periods of time shown in the graph.

Adhesion

[0099] The foregoing results from Example 1 to 4 show that use of a copolymer substrate with a covalently linked Type II photoinitiator can provide broadband reflection and good adherence to a copolymer substrate. Example 1 is illustrative of a coating that does not delaminate, but that is narrowband. But when generating broadband multilayers, a too-high photoinitiator concentration (10 wt% in the primer) generates severe misalignment of the LCP as shown in Example 2, FIG. 3. When a too-low concentration of photoinitiator (0.5 wt% in ethanol) are used, alignment is improved as shown in Example 3, FIG. 4. However, without being bound by theory, it is believed that after photoinitiator diffusion from the primer layer and curing to form the film, there is not enough photoinitiator remaining at the substrate-coating interface to ensure good adhesion. Thus, when a copolymer substrate with a covalently linked Type II photoinitiator is used in combination with a low BP primer concentration, excellent alignment, and improved adhesion to the copolymer substrate after base treatment are achieved.

Haze

[0100] Haze measurements of the films of Examples 2, 3, and 4 were determined using the ASTM standard D-1003-00 (Perkin Elmer Lambda 750 ETV-VIS-NIR spectrophotometer). Two films per example (a total of 6 films) were analyzed, with 10 measurements per film. A statistical analysis of the results using Minitab® software was performed. Although the number of data points and samples used is relatively limited, the data show that generally, the haze and transparency levels of films prepared with 0.5 wt% of benzophenone-ethanol solutions were comparable, irrespective of the type of substrate used (Examples 3 and 4), and on the order of 47-49% (haze) and 83-84% (transparency). Comparison of the means showed that the haze level of Examples 3 and 4 was statistically significantly lower that of Example 2 (PC substrate and 10 wt% bisphenol-ethanol solution - 56% haze) and that the transparency level of Examples 3 and 4 was higher than that of Example 2 (about 80% transparency).

[0101] No significant difference in terms of spread (i.e., the standard deviation measured over the surface of the films) of haze or transparency levels was found between samples prepared with 0.5 or 10 wt% BP solutions (Ex. 3/4 and 2, respectively), regardless of the substrate choice (PC homopolymer vs. BPA-DHBP copolymer). Consequently, at least at laboratory scale, the photoinitiator concentration in the primer layer used to create the pitch gradient may not be the main factor governing the film homogeneity as reflected in optical properties.

[0102] The invention is further illustrated by the following aspects, which are not intended to limit the claims.

[0103] Aspect 1. A layered article, comprising a copolymer substrate comprising a covalently linked Type II photoinitiator; and a temperature-responsive, cholesteric LCP film chemisorbed to a surface of the copolymer substrate, wherein the LCP film has a broadband response at a relative humidity of 60% to 95%.

[0104] Aspect 2. The layered article of aspect 1, wherein the shift of the broadband response is 50 to 600 nanometers, or 50 to 400 nanometers, or 100 to 400 nanometers, or 200 to 400 nanometers.

[0105] Aspect 3. The layered article of aspect 1 or aspect 2, wherein the LCP film is disposed directly on the copolymer substrate.

[0106] Aspect 4. The layered article of any one of aspects 1 to 3, comprising no additional layer disposed on a side of the film opposite the copolymer substrate, or no additional layer disposed on a side of the film opposite the copolymer substrate, or both.

[0107] Aspect 5. The layered article of any one of aspects 1 to 3, comprising an additional layer disposed on a side of the LCP film opposite the copolymer substrate, or an additional layer disposed on a side of the copolymer substrate opposite the liquid crystal polymer, or both.

[0108] Aspect 6. The layered article of any one of aspects 1 to 5, wherein a cholesteric pitch of the liquid crystal film is present as a gradient effective to widen the photonic reflection band, preferably wherein the gradient decreases in pitch in a direction away from the substrate e.

[0109] Aspect 7. The layered article of any one of aspects 1 to 6, wherein the liquid crystal film has a thickness of 1 to 100 micrometers, preferably 10 to 50 micrometers.

[0110] Aspect 8. A method of forming the layered article of any one of aspects 1 to 7, the method comprising: providing a copolymer substrate having opposed first and second sides, and comprising a Type II photoinitiator covalently linked to the polymer of the substrate;

applying a primer composition comprising 0.1 to 7 weight percent, preferably 0.1 to 2 weight percent of a Type II photoinitiator onto a first surface area of the first side of the copolymer substrate to form a primer layer; applying a coating composition comprising a liquid crystal monomer composition onto at least a portion of the primer layer under shear to provide an aligned coating layer; irradiating the aligned coating layer on the second side of the copolymer substrate and through the substrate to form a liquid crystalline polymer film on the substrate; and treating the liquid crystalline film with an aqueous base.

[0111] Aspect 9. The method of aspect 8, wherein applying the primer layer comprises printing, slot die coating, spraying, or dip coating the substrate with the primer composition; and applying the coating composition comprises using a doctor blade, printing, or a slot die coating.

[0112] Aspect 10. The method of any one of aspects 8 to 9, wherein the copolymer substrate comprises a copolycarbonate, preferably wherein the copolycarbonate comprises bisphenol A units and benzophenone units.

[0113] Aspect 11. The method of any one of aspects 8 to 10, wherein the Type II photoinitiator of the primer layer comprises a benzophenone, a thioxanthone, a xanthone, a quinone, or a combination thereof, preferably wherein the Type II photoinitiator of the primer layer is the same as Type II photoinitiator of the copolymer substrate.

[0114] Aspect 12. The method of any one of aspects 8 to 11, wherein the crystalline monomer composition comprises a bifunctional chiral liquid crystal monomer, a polyfunctional crosslinking liquid crystal monomer, and a carboxylic acid-containing monomer capable of dimerizing to a liquid crystal monomer.

[0115] Aspect 13. An article comprising the layered article of any one of aspects 1 to 12, preferably wherein the article is a window.

[0116] Aspect 14. A window, comprising: a frame; and a sheet supported by the frame, wherein the sheet comprises the layered article of any one of aspects 1 to 12.

[0117] The singular forms“a,”“an,” and“the’ include plural referents unless the context clearly dictates otherwise. The term“or” means“and/or” unless clearly indicated otherwise by context. The term“comprising” can include the aspects“consisting of’ and“consisting essentially of.” The terms“comprise(s),”“include(s),”“having,”“has, ”“can,”“contain(s),” and variants thereof are open-ended, requiring the presence of the named ingredients/steps and permitting the presence of other ingredients/steps. However, such description should be construed as also describing compositions or processes as“consisting of’ and“consisting essentially of’ the enumerated ingredients/steps, which allows the presence of only the named ingredients/steps, along with any impurities that might result therefrom.

[0118] Numerical values in this application, particularly as they relate to polymers or polymer compositions, reflect average values for a composition that may contain individual polymers of different characteristics. Unless indicated to the contrary, the numerical values include numerical values that are the same when reduced to the same number of significant figures and numerical values that differ from the stated value by less than the experimental error of conventional measurement technique of the type described herein to determine the value, or a tolerance in manufacture. All ranges disclosed herein are inclusive of the recited endpoint and are independently combinable (e.g., the range of“from 2 to 10 g, preferably 3 to 7 g” is inclusive of the endpoints, 2 g, 7 g, and 10 g, the ranges such as 3 to 10 g, and all the

intermediate values).

[0119] Compounds are described using standard nomenclature. Any position not substituted by any indicated group is understood to have its valency filled by a bond as indicated, or a hydrogen atom.“Aliphatic” means a cyclic, linear, or branched, saturated, or unsaturated array of atoms that is not aromatic and contains only C or H, except for any substituents. Exemplary aliphatic groups include methyl, ethyl, isopropyl, hexyl, and

cyclohexyl.“Aromatic” means a group having a ring system containing a delocalized conjugated pi system with a number of pi-electrons that obeys HiickeTs Rule. The ring system can include heteroatoms such as N, P, S, Se, Si, or O, or only C and H. Exemplary aromatic groups include phenyl, pyridyl, furanyl, thienyl, naphthyl, and biphenyl.

[0120] The term“alkyl” means a wholly unsaturated aliphatic group (except for any substitutions), and can be linear, branched, or cyclic.“Amino” means a radical of the formula - NR.2, where each R is alkyl.“Halogen” means fluorine, chlorine, bromine, and iodine.“Alkoxy” means an alkyl group attached to an oxygen atom, i.e. -OCiTEn+i . The term“nitrile” means a radical of the formula -CN, wherein the carbon atom is covalently bonded to another carbon- containing group.“(Meth)acrylate group” means a radical of the formula CH2=C(H or C¾)- C(=0)— O— .“Substituted” means at least one hydrogen atom on the named group is substituted with another functional group, such as halogen, -OH, -CN, or -NO2. An exemplary substituted alkyl group is hydroxyethyl. The number of carbon atoms is exclusive of any substituents.

[0121] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. All cited patents, patent applications, and other references are incorporated herein by reference in their entirety, but if a term in this application conflicts with a term in the incorporated reference, the meaning from this application takes precedence over the conflicting term from the incorporated reference.

[0122] The materials, methods, and examples disclosed herein are illustrative only and not intended to be limiting. Preferred methods and materials are described herein, although methods and materials similar or equivalent to those described herein can be used in practice or testing of the present disclosure.