Prior Applications [0001] This application claims the benefit of U.S. Patent Application No. 10/859,784, filed on June 3, 2004, the description of which is incorporated by reference herein. Field of the Invention [0002] This invention relates generally to thermoplastics and articles formed therefrom. More particularly, in certain embodiments, the invention relates to intimate physical mixtures of macrocyclic polyester oligomer and filler. Background of the Invention [0003] Semi-crystalline polymers are useful as engineering thermoplastics because they possess advantageous chemical, physical, and electrical properties, and because they can be readily processed by thermal means. For example, linear semi-crystalline polymers such as polyethylene terephthalate (PET) and polybutylene terephthalate (PBT) are processed by injection molding and extrusion in the manufacture of plastic components. [0004] It is important that semi-crystalline polymers be heat resistant, because they are typically processed at high temperature. Heat deflection temperature (HDT) is a measure of the short-term heat resistance of a material. The heat deflection temperature distinguishes between materials that are able to sustain light loads at high temperatures and those that lose their rigidity over a narrow temperature range. Thus, a high heat deflection temperature is indicative of a material whose modulus (i.e. Young's modulus) is high over a wide temperature range. [0005] It is of interest, therefore, to increase the heat deflection temperature of polymeric materials without substantially affecting other desired properties of the material. Similarly, it is desired to increase the modulus of a material over a wide temperature range without substantially affecting other desired properties of the material. [0006] Certain fillers have been added to polymer compositions in an attempt to increase heat deflection temperature. Fillers that have been added to polymer compositions include fibrous fillers with high modulus, such as fiberglass and carbon fiber, as well as non-fibrous fillers such as calcium carbonate, wollastonite, and mica. However, the addition of filler to a polymer will generally have a negative impact on other properties of the resulting polymer composition, such as ductility, impact strength, and toughness. Furthermore, it is a general rule that the more filler that is added, the greater its impact on the properties of the polymer composition. [0007] Fillers with high aspect ratio have been investigated, because lesser amounts of these fillers are generally needed to produce a desired modulus-increasing effect for a given polymer composition. However, there are a number of problems resulting from the use of high-aspect- ratio fillers. It is typically more difficult to incorporate fillers with high aspect ratio into polymer. Often, the filler is not compatible with the polymer, and stable, highly-disperse mixtures of the filler in the polymer are difficult or impossible to achieve. [0008] Macrocyclic polyester oligomer (macrocyclic oligoester, MPO) has unique properties that make it attractive as a matrix-forming resin for engineering thermoplastic composites. For example, MPO generally exhibits low melt viscosity and can polymerize at temperatures well below the melting point of the resulting polymer. An MPO of particular interest is macrocyclic poly(l ,4-butylene terephthalate) oligomer. [0009] It has been shown that mixtures of macrocyclic poly(l ,4-butylene terephthalate) oligomer and organically-modified montmorillonite (a form of aluminosilicate) can be polymerized to produce a polymeric composition with high modulus (see, e.g. U.S. Patent No. 5,707,439, by Takekoshi et al.). However, montmorillonite must be modified by cation exchange prior to incorporation with the MPO. Summary of the Invention [0010] It has been discovered that anhydrous magnesium silicate (talc) is highly compatible with certain macrocyclic polyester oligomers (MPO), and may be homogeneously dispersed into MPO without undergoing modification by ion exchange or other surface treatment. [0011] Accordingly, the invention provides intimate physical mixtures of macrocyclic polyester oligomer (MPO) with unmodified, high-aspect-ratio filler, as well as methods for preparing and using such mixtures, hi particular, the invention provides mixtures of MPO with anhydrous magnesium silicate (anhydrous talc), which can be polymerized to form polymer compositions having advantageous properties. [0012] Because of the unexpectedly high compatibility of anhydrous magnesium silicate filler with MPO, improved dispersion of the filler in a polymer matrix can be achieved upon polymerization of the MPO in the MPO-filler mixture; and because of the low viscosity associated with MPO, larger amounts of high-aspect-ratio filler can be used therein. Polymer compositions made from MPO-filler mixtures exhibit significantly higher elastic modulus than unfilled, polymerized MPO over a broad temperature range, indicating improved heat resistance, processibility, stiffness, and strength in a wide variety of processing environments. Furthermore, the presence of the filler in the MPO composite does not significantly affect the polymerization rate of the MPO, nor is percent conversion or average molecular weight of the resulting polymer significantly affected. [0013] Thus, in one aspect, the invention provides a mixture including an MPO and a filler, where the filler comprises a magnesium silicate. The magnesium silicate is preferably anhydrous. The mixture may be an intimate physical mixture or a nanocomposite, for example. - A - In a preferred embodiment, the filler dissolves in the mixture. The filler may be present in the mixture in any amount, for example, in an amount of at least about 10 wt.%, at least about 20 wt.%, at least about 30 wt.%, or at least about 40 wt.%, greater than about 40 wt.%, greater than about 50 wt.%, greater than about 60 wt.%, greater than about 70 wt.%, or more. [0014] In one embodiment, the polymer produced from the MPO-filler mixture exhibits a higher elastic modulus than the polymer produced from the unfilled MPO over a wide temperature range - for example, at least over a temperature range from about 250C to about 50°C, from about 25°C to about 100°C, from about 250C to about 150°C, from about 25°C to about 200°C, from about 100C to about 500C, from about 10°C to about 1000C, from about 100C to about 1500C, or from about 100C to about 2000C. [0015] The MPO in the mixture may include one or more species. The species may have different degrees of polymerization, hi one embodiment, the MPO includes butylene terephthalate units and oxydiethylene terephthalate units. [0016] In one embodiment, the mixture further includes an MPO polymerization catalyst - for example, a tin compound, such as butyltin chloride dihydroxide, or a titanate compound. Mixtures of the invention (both with and without catalyst) are preferably stable under ambient conditions (at room temperature in air) for at least a week, and may be stable at least a month, at least a year, or even longer under ambient conditions. In one embodiment, the invention provides a polymer composition resulting from polymerization of one or more components of a mixture of the invention. In one embodiment, the invention provides an article of manufacture produced by polymerizing a mixture of the invention. [0017] In another aspect, the invention provides a method for preparing an intimate physical mixture of MPO and anhydrous magnesium silicate, the method comprising the step of contacting the MPO and anhydrous magnesium silicate at a temperature at which the MPO is at least partially melted. In one embodiment, the temperature is within a range from about 15O0C to about 190°C. The MPO may be contacted with the talc before, during, or after the MPO melts. Preferably, the anhydrous magnesium silicate dissolves in the mixture. [0018] The mixture may be polymerized, for example, in a two-part system, where the polymer-filler mixture is exposed to a temperature sufficient to melt the MPO, and the resulting mixture is contacted with a polymerization catalyst whereupon polymerization and crystallization occur substantially isothermally, thereby forming a polymeric composition comprising polymer and filler. The polymerization may take place in any molding, casting, or forming process, for example, an injection molding process, a rotational molding process, a resin film infusion process, a solvent prepreg process, a hot melt prepreg process, an extrusion process, a pultrusion process, a resin transfer molding process, a filament winding process, a compression molding process, a roll wrapping process, a powder coating process, and combinations thereof. The time and expense required to thermally cycle a tool is favorably reduced, for example, because demolding can take place immediately following polymerization, without first cooling the mold. [0019] Alternatively, the MPO-filler mixture may be stored as a one-part, ready-to-polymerize blend comprising MPO, filler, and a polymerization catalyst. The one-part blend remains stable for at least a week, for at least a month, or for at least a year or more, without significant premature polymerization of MPO and without significant deactivation of catalyst. When it is desired to polymerize the MPO, the one-part blend is exposed to a temperature sufficient to melt and polymerize the MPO, whereupon polymerization and crystallization occur substantially isothermally. [0020] In yet another aspect, the invention provides a method for polymerizing an MPO, the method comprising the steps of providing a mixture comprising MPO, a polymerization catalyst, and a layered mineral, and heating the mixture to polymerize at least one component of the mixture. The layered mineral preferably comprises a silicate, and more preferably comprises magnesium silicate. In one embodiment, the layered mineral is present in the mixture in an amount of at least about 10 wt.%, at least about 20 wt.%, at least about 30 wt.%, at least about 40 wt.%, greater than about 40 wt.%, greater than about 50 wt.%, greater than about 60 wt.%, or greater than about 70 wt.%, although amounts less than 10 wt.%, and amounts greater than 70 wt.% may be used as well. [0021] It is believed that the compatibility of anhydrous magnesium silicate with MPO may be related to the surface energy, charge neutrality, and/or the non-polarity of platelets of anhydrous magnesium silicate. The polar -OH groups of anhydrous talc reside in the interior of the structure of a talc layer and, therefore, are not chemically accessible to the molecules at or near the surface of the talc layer. Other factors that may be related to the compatibility of the filler with MPO include the platyness, softness, hydrophobicity, organophilicity, inertness, and mineralogical composition of the filler. [0022] Thus, in still another aspect, the invention is directed to an intimate physical mixture comprising an MPO and a layered mineral, where the layered mineral has a non-polar, charge- neutral surface. In one embodiment, the layered mineral comprises at least one of molybdenum sulfide, graphite, magnesium, iron, calcium, potassium, sodium, manganese, titanium, zirconium, copper, berylium, and zinc. The intimate physical mixture may also contain a catalyst, and may be stable at ambient conditions for at least one week, at least one month, or longer. [0023] In another aspect, the invention provides a mixture including an MPO and talc. In one embodiment, the mixture contains other compounds in addition to MPO and talc. The talc typically contains magnesium silicate, but may additionally contain other compounds, hi one embodiment, the talc is magnesium silicate. In one embodiment, the talc is anhydrous magnesium silicate. The mixture may be an intimate physical mixture or a nanocomposite, for example. In a preferred embodiment, the talc dissolves in the mixture. The talc may be present in the mixture in any amount, for example, in an amount of at least about 10 wt.%, at least about 20 wt.%, at least about 30 wt.%, or at least about 40 wt.%, greater than about 40 wt.%, greater than about 50 wt.%, greater than about 60 wt.%, greater than about 70 wt.%, or more. [0024] In one embodiment, a polymer composition produced from the MPO-talc mixture exhibits a higher elastic modulus than polymer produced from the MPO without the talc over a wide temperature range - for example, at least over a temperature range from about 25°C to about 50°C, from about 25°C to about 1000C, from about 250C to about 1500C, from about 25°C to about 2000C, from about 100C to about 5O0C, from about 1O0C to about 1000C, from about 100C to about 1500C, or from about 1O0C to about 2000C. In one embodiment, the polymer composition exhibits a higher elastic modulus than polymer produced from the MPO without the talc at temperatures above about 100C, above about 25°C, or above about 500C, for example. In one embodiment, the polymer composition exhibits a higher elastic modulus than polymer produced from the MPO without the talc at temperatures below about 2000C, below about 1500C, or below about 1000C, for example. In one embodiment, the polymer composition exhibits a higher heat deflection temperature (HDT) than polymer produced from the MPO without the talc. [0025] The MPO in the mixture may include one or more species. The species may have different degrees of polymerization. In one embodiment, the MPO includes butylene terephthalate units and oxydiethylene terephthalate units. [0026] In one embodiment, the mixture further includes an MPO polymerization catalyst - for example, a tin compound, such as butyltin chloride dihydroxide. In one embodiment, the catalyst comprises a titanate compound. Mixtures of the invention (both with and without catalyst) are preferably stable under ambient conditions (at room temperature in air) for at least a week, and may be stable at least a month, at least a year, or even longer under ambient conditions. In one embodiment, the invention provides a polymer composition resulting from polymerization of one or more components of a mixture of the invention. In a preferred embodiment, the polymer composition is a nanocomposite. In one embodiment, the invention provides an article of manufacture produced by polymerizing a mixture of the invention. [0027] In another aspect, the invention provides a method for preparing an intimate physical mixture of MPO and talc, the method comprising the step of contacting the MPO and talc (and, optionally, one or more additional compounds) at a temperature at which the MPO is at least partially melted. In one embodiment, the temperature is within a range from about 15O0C to about 190°C. In one embodiment, the temperature is below about 250°C, below about 200°C, below about 190°C, below about 18O0C, or below about 17O0C, for example. The MPO may be contacted with the talc before, during, or after the MPO melts. Preferably, the talc dissolves in the mixture. The talc typically contains magnesium silicate, but may additionally contain other compounds, hi one embodiment, the talc is magnesium silicate. In one embodiment, the talc is anhydrous magnesium silicate. In one embodiment, the talc has a substantially charge-neutral surface. In one embodiment, the intimate physical mixture contains at least about 10 wt.% talc, at least about 20 wt.% talc, at least about 30 wt.% talc, at least about 40 wt.% talc, greater than about 40 wt.% talc, greater than about 50 wt.% talc, greater than about 60 wt.% talc, greater than about 70 wt.% talc, or more. In one embodiment, the MPO is at least partially melted prior to the contacting step. In one embodiment, the MPO melts during the contacting step. In a preferred embodiment, the intimate physical mixture is a nanocomposite. In one embodiment, the intimate physical mixture further comprises a polymerization catalyst. In one embodiment the method further includes the step of heating the intimate physical mixture to polymerize the MPO. In one embodiment, the polymerized product is a nanocomposite. In one embodiment, the method produces polymer composition that exhibits a higher heat deflection temperature (HDT) than a polymer resulting from the polymerization of the MPO without the talc. [0028] The mixture may be polymerized, for example, in a two-part system, where the MPO- talc mixture is exposed to a temperature sufficient to melt the MPO, and the resulting mixture is contacted with a polymerization catalyst whereupon polymerization and crystallization occur substantially isothermally, thereby forming a polymeric composition comprising polymer and talc. The polymerization may take place in any molding, casting, or forming process, for example, an injection molding process, a rotational molding process, a resin film infusion process, a solvent prepreg process, a hot melt prepreg process, an extrusion process, a pultrusion process, a resin transfer molding process, a filament winding process, a compression molding process, a roll wrapping process, a powder coating process, and combinations thereof. The time and expense required to thermally cycle a tool is favorably reduced, for example, because demolding can take place immediately following polymerization, without first cooling the mold. [0029] Alternatively, the MPO-talc mixture may be stored as a one-part, ready-to-polymerize blend comprising MPO, talc, and a polymerization catalyst. The one-part blend remains stable for at least a week, for at least a month, or for at least a year or more, without significant premature polymerization of MPO and without significant deactivation of catalyst. When it is desired to polymerize the MPO, the one-part blend is exposed to a temperature sufficient to melt and polymerize the MPO, whereupon polymerization and crystallization occur substantially isothermally. [0030] It is believed that the compatibility of talc with MPO may be related to the surface energy, charge neutrality, and/or the non-polarity of platelets of talc, or, preferably, anhydrous talc. The polar —OH groups of talc reside in the interior of the structure of a talc layer and, therefore, are not chemically accessible to the molecules at or near the surface of the talc layer. Other factors that may be related to the compatibility of the filler with MPO include the platyness, softness, hydrophobicity, organophilicity, inertness, and mineralogical composition of the filler. [0031] Thus, in another aspect, the invention is directed to an intimate physical mixture comprising an MPO and a layered mineral, where the layered mineral has a substantially non- polar, substantially charge-neutral surface, and the layered mineral is present in the intimate physical mixture in an amount of at least about 10 wt.%. The MPO may comprise one or more species. In a preferred embodiment, the intimate physical mixture is a nanocomposite. In one embodiment, the layered mineral comprises at least one of molybdenum sulfide, graphite, magnesium, iron, calcium, potassium, sodium, manganese, titanium, zirconium, copper, berylium, and zinc. In one embodiment, the layered mineral comprises a layered silicate. In one embodiment, the layered silicate is talc. The layered mineral may be present in the mixture in an amount of at least about 10 wt.%, at least about 20 wt.%, at least about 30 wt.%, at least about 40 wt.%, greater than about 40 wt.%, greater than about 50 wt.%, greater than about 60 wt.%, greater than about 70 wt.%, or more. The intimate physical mixture may also contain a catalyst. The intimate physical mixture (with or without the catalyst) may be stable at ambient conditions for at least one week, at least one month, or longer. Brief Description of the Drawings [0032] The objects and features of the invention can be better understood with reference to the drawings described below, and the claims. [0033] Figure 1 shows a graph depicting results of dynamic mechanical thermal analysis (DMTA) tests of illustrative polymer compositions of the invention containing 0 wt.%, 10 wt.%, and 30 wt.% anhydrous magnesium silicate. ^

- 11 - [0034] Figure 2 shows a graph depicting results of DMTA tests of illustrative polymer compositions of the invention containing 0 wt.%, 30 wt.%, and 60 wt.% milled glass. [0035] Figure 3 shows a graph depicting further results of DMTA tests of illustrative polymer compositions of the invention containing 0 wt.%, 30 wt.%, and 60 wt.% milled glass. Detailed Description [0036] It has been discovered that substantially pure, anhydrous magnesium silicate dissolves in molten macrocyclic poly(l,4-butylene terephthalate) oligomer at a temperature within a range from about 15O0C to about 190°C, resulting in a homogeneous, transparent liquid. The discovery is unexpected, because attempts to incorporate aluminosilicate fillers into polymers have required that the aluminosilicate platelet surface be modified in order to compatibilize the filler with the polymer matrix. Unlike montmorillonite, for example, the magnesium silicate of the present invention does not require modification by cation exchange prior to incorporation with MPO. [0037] Upon cooling to ambient temperature, a solution of macrocyclic poly(l,4-butylene terephthalate) oligomer and magnesium silicate hardens into a transparent solid, indicating the silicate is dispersed in the mixture well enough to allow light to penetrate the mixture. That is, an average-sized filler particle in the resulting intimate physical mixture has at least one dimension (i.e. length, width, and/or height) that is less than roughly 400 nm (0.4 micron), the shortest wavelength of visible light. In one embodiment, a near-molecular blend of MPO and filler is achieved, and the intimate physical mixture is a nanocomposite. In the context of plastics, a nanocomposite is a near-molecular blend of (1) polymer molecules and (2) nano-scale particles, where a nanoscale particle is a material with at least one dimension in the nanometer range. [0038] The intimate physical mixture is stable, and the filler remains dispersed in the mixture for at least a week, for at least a month, or for at least a year or more under ambient conditions. A long shelf life enhances the versatility of the mixture. For example, the mixture may be stored for a long period of time, without requiring refrigeration or storage in an oxygen-free environment, before the mixture is polymerized in the manufacture of a plastic component. [0039] It has been further discovered that polymer compositions formed from intimate physical mixtures of magnesium silicate and MPO exhibit increased Young's modulus (E1) over a wide range of temperature, for example, from about 25°C to about 160°C, as well as higher heat deflection temperatures (HDT), indicating an improved heat resistance of the filler- containing polymer composition compared with the unfilled polymer. In certain embodiments, the invention provides methods of filling polymer so as to increasing its HDT value by 10%, 20%, 30%, 40%, 50%, 75%, 100%, or more. [0040] Furthermore, it is possible to incorporate large amounts of high-aspect-ratio filler in the mixture, for example, because: (1) the filler and MPO are highly compatible (depending on the filler used, the filler may actually dissolve in the MPO), (2) the filler can be melt-mixed with MPO at a relatively low temperature, and (3) the MPO has a very low melt viscosity. Since MPO melts at relatively low temperatures, it is possible to avoid or limit the exposure of the mixture components to high temperature during incorporation of filler and/or catalyst. Surprisingly, the presence of the filler in the blend: (1) does not substantially decrease the rate of polymerization of the MPO contained in the blend, (2) does not substantially reduce the ultimate conversion of MPO to polymer, and (3) does not affect the ability of the blend to polymerize and crystallize essentially isothermally at polymerization temperatures. [0041] In addition to mixtures of MPO with talc and/or other layered minerals, the invention also provides mixtures of MPO with certain other fillers, such as milled glass fiber, in which the presence of the filler increases HDT and increases the elastic modulus of the mixture over a wide temperature range. These fillers may be used alone, or in combination, at levels of up to about 30 wt.%, greater than about 30 wt.%, greater than about 40 wt.%, greater than about 50 wt.%, greater than about 60 wt.%, greater than about 70 wt.%, greater than about 80 wt.%, greater than about 90 wt.%, or even more, where weight percent is based on the total weight of the MPO- filler mixture. [0042] Throughout the description, where compositions, mixtures, blends, and composites are described as having, including, or comprising specific components, or where processes and methods are described as having, including, or comprising specific steps, it is contemplated that, additionally, there are compositions, mixtures, blends, and composites of the present invention that consist essentially of, or consist of, the recited components, and that there are processes and methods of the present invention that consist essentially of, or consist of, the recited processing steps. [0043] It should be understood that the order of steps or order for performing certain actions is immaterial so long as the invention remains operable. Moreover, two or more steps or actions may be conducted simultaneously. [0044] The following general definitions may be helpful in understanding the various terms and expressions used in this specification. Definitions [0045] As used herein, "macrocyclic" is understood to mean a cyclic molecule having at least one ring within its molecular structure that contains 5 or more atoms covalently connected to form the ring. [0046] As used herein, an "oligomer" is understood to mean a molecule that contains one or more identifiable structural repeat units of the same or different formula. [0047] As used herein, a "macrocyclic polyester oligomer" is understood to mean a macrocyclic oligomer containing structural repeat units having an ester functionality. A macrocyclic polyester oligomer typically refers to multiple molecules of one specific repeat unit formula. However, a macrocyclic polyester oligomer also may include multiple molecules of different or mixed formulae having varying numbers of the same or different structural repeat units. In addition, a macrocyclic polyester oligomer may be a co-polyester or multi-component polyester oligomer, i.e., an oligomer having two or more different structural repeat units having ester functionality within one cyclic molecule. [0048] As used herein, "substantially homo- or co-polyester oligomer" is understood to mean a polyester oligomer wherein the structural repeat units are substantially identical or substantially composed of two or more different structural repeat units, respectively. [0049] As used herein, an "alkylene group" is understood to mean -CnH2n-, where n > 2. [0050] As used herein, a "cycloalkylene group" is understood to mean a cyclic alkylene group, -CnH2n-X-, where x represents the number of H's replaced by cyclization(s). [0051] As used herein, a "mono- or polyoxyalkylene group" is understood to mean [-(CH2)m- O-]n-(CH2)m-, wherein m is an integer greater than 1 and n is an integer greater than 0. [0052] As used herein, a "divalent aromatic group" is understood to mean an aromatic group with links to other parts of the macrocyclic molecule. For example, a divalent aromatic group may include a meta- or para- linked monocyclic aromatic group (e.g., benzene). [0053] As used herein, an "alicyclic group" is understood to mean a non-aromatic hydrocarbon group containing a cyclic structure within. [0054] As used herein, a "Ci-4 primary alkyl group" is understood to mean an alkyl group having 1 to 4 carbon atoms connected via a primary carbon atom. [0055] As used herein, a "C1-I0 alkyl group" is understood to mean an alkyl group having 1 to 10 carbon atoms, including straight chain or branched radicals. [0056] As used herein, a "methylene group" is understood to mean -CH2-. [0057] As used herein, an "ethylene group" is understood to mean -CH2-CH2-. [0058] As used herein, a "C2-3 alkylene group" is understood to mean -CnH2n-, where n is 2 or 3. [0059] As used herein, a "C2-6 alkylene group" is understood to mean -CnH2n-, where n is 2-6. [0060] As used herein, "substitute phenyl group" is understood to mean a phenyl group having one or more substituents. A substituted phenyl group may have substitution pattern that is recognized in the art. For example, a single substituent may be in the ortho, meta or para positions. For multiple substituents, typical substitution patterns include, for example, 2,6-, 2,4,6-, and, 3,5- substitution patterns. [0061] As used herein, a "filler" is understood to mean a material other than a macrocyclic polyester oligomer or a polymerization catalyst that may be included in the blend material. A filler may be used to achieve a desired purpose or property, and may be present or transformed into known and/or unknown substances in the resulting polyester polymer. For example, the purpose of the filler may be to provide stability, such as chemical, thermal, or light stability, to the blend material or the polyester polymer product (i.e. to increase E' over a wide temperature range and/or to increase HDT), and/or to increase the strength of the polyester polymer product. A filler also may provide or reduce color, provide weight or bulk to achieve a particular density, provide reduced gas and vapor permeability, provide flame or smoking resistance (i.e., be a flame retardant), be a substitute for a more expensive material, facilitate processing, and/or provide other desirable properties. Illustrative examples of fillers are, among others, anhydrous magnesium silicate (anhydrous talc), fumed silica, titanium dioxide, calcium carbonate, wollastonite, chopped fibers, fly ash, glass, glass fiber, milled glass fiber, glass microspheres, micro-balloons, crushed stone, nanoclay, linear polymers, and monomers. [0062] As used herein, a "polymer composition" is understood to mean a polymeric material comprising filler. [0063] The following headers are provided as a general organizational guide and do not serve to limit support for any given element of the invention to a particular section of the Description. I. Macrocyclic Polyester Oligomer [0064] One of the ingredients of the mixtures of the invention is a macrocyclic polyester oligomer. Many different macrocyclic polyester oligomers can readily be made and are useful in the practice of this invention. Thus, depending on the desired properties of the final polymer composition, the appropriate macrocyclic polyester oligomer(s) can be selected for use in its manufacture. [0065] Macrocyclic polyester oligomers that may be employed in this invention include, but are not limited to, macrocyclic poly(alkylene dicarboxylate) oligomers having a structural repeat unit of the formula: O O -O ■o- -B- where A is an alkylene, or a cycloalkylene or a mono- or polyoxyalkylene group; and B is a divalent aromatic or alicyclic group. [0066] Preferred macrocyclic polyester oligomers include macrocyclic poly( 1 ,4-butylene terephthalate) (PBT), ρoly( 1 ,3 -propylene terephthalate) (PPT), ρoly( 1 ,4- cyclohexylenedimethylene terephthalate) (PCT), poly(ethylene terephthalate) (PET), and poly(l,2-ethylene 2,6-naphthalenedicarboxylate) (PEN) oligomers, and copolyester oligomers comprising two or more of the above monomer repeat units. [0067] Macrocyclic polyester oligomers may be prepared by known methods. Synthesis of the preferred macrocyclic polyester oligomers may include the step of contacting at least one diol of the formula HO-A-OH with at least one diacid chloride of the formula:

where A and B are as defined above. The reaction typically is conducted in the presence of at least one amine that has substantially no steric hindrance around the basic nitrogen atom. An illustrative example of such amines is l,4-diazabicyclo[2.2.2]octane (DABCO). The reaction usually is conducted under substantially anhydrous conditions in a substantially water immiscible organic solvent such as methylene chloride. The temperature of the reaction typically is between about -250C and about 250C. See, e.g., U.S. Patent No. 5,039,783 to Brunelle et al. [0068] Macrocyclic polyester oligomers have also been prepared via the condensation of a diacid chloride with at least one bis(hydroxyalkyl) ester such as bis(4-hydroxybutyl) terephthalate in the presence of a highly unhindered amine or a mixture thereof with at least one other tertiary amine such as triethylamine, in a substantially inert organic solvent such as methylene chloride, chlorobenzene, or a mixture thereof. See, e.g., U.S. Patent No. 5,231,161 to Brunelle et al. [0069] Another method for preparing macrocyclic polyester oligomers or macrocyclic copolyester oligomers is to depolymerize linear polyester polymers in the presence of an organotin or titanate compound. In this method, linear polyesters are converted to macrocyclic polyester oligomers by heating a mixture of linear polyesters, an organic solvent, and a trans- esterification catalyst such as a tin or titanium compound. The solvents used, such as o-xylene and o-dichlorobenzene, usually are substantially free of oxygen and water. See, e.g., U.S. Patent Nos. 5,407,984 to Brunelle et al and 5,668,186 to Brunelle et al. [0070] Macrocyclic polyester oligomers (macrocyclic oligoesters) have been prepared from intermediate molecular weight polyesters by contacting a dicarboxylic acid or a dicarboxylate in the presence of a catalyst to produce a composition comprising a hydroxyalkyl-terminated polyester oligomer. The hydroxyalkyl-terminated polyester oligomer is heated to produce a composition comprising an intermediate molecular weight polyester which preferably has a molecular weight between about 20,000 Daltons and about 70,000 Daltons. The intermediate molecular weight polyester is heated and a solvent is added prior to or during the heating process to produce a composition comprising an MPO. See, e.g., U.S. Patent No. 6,525,164, to Faler. [0071] Macrocyclic polyester oligomers (macrocyclic oligoesters) that are substantially free from macrocyclic co-oligoesters have been prepared by depolymerizing polyesters using the organo-titanate catalysts described in co-owned U.S. Patent Application No. 09/974,722, by Phelps et al., published as U.S. Patent Application Publication No. US 2003/0114640, the text of which is incorporated by reference herein in its entirety. [0072] It is also within the scope of the invention to employ macrocyclic homo- and co- polyester oligomers to produce homo- and co-polyester polymers, respectively. Therefore, unless otherwise stated, an embodiment of a composition, article, process, or method that refers to a macrocyclic polyester oligomer also includes a co-polyester embodiments. [0073] In one embodiment, macrocyclic ester homo- and co-oligomers used in this invention include oligomers having a general structural repeat unit of the formula: O I l O— A1— C where A' is an alkylene, cycloalkylene, or mono- or polyoxyalkylene group, and where A' may be substituted, unsubstituted, branched, and/or linear. Example MPO's of this type include butyrolactone and caprolactone, where the degree of polymerization is one, and 2,5-dioxo-l,4- dioxane, and lactide, where degree of polymerization is two. The degree of polymerization may alternatively be 3, 4, 5, or higher. Molecular structures of 2,5-dioxo-l,4-dioxane and lactide, respectively, appear below:

[0074] In one embodiment, a macrocyclic polyester oligomer (MPO) used in a mixture of the invention includes species of different degrees of polymerization. Here, a degree of polymerization (DP) with respect to the MPO means the number of identifiable structural repeat units in the oligomeric backbone. The structural repeat units may have the same or different molecular structure. For example, an MPO may include dimer, trimer, tetramer, pentamer, and/or other species. II. Polymerization Catalyst [0075] Polymerization catalysts employed in the invention are capable of catalyzing the polymerization of the macrocyclic polyester oligomer. As with state-of-the-art processes for polymerizing macrocyclic polyester oligomers, organotin and organotitanate compounds are the preferred catalysts, although other catalysts may be used. For example, organotin compound lJjβjό-tetra-n-butyl-ljβ-distanna^jS^jlO-tetraoxacyclodec ane may be used as polymerization catalyst. Other illustrative organotin compounds include n-butyltin(IV) chloride dihydroxide, dialkyltin(IV) oxides, such as di-n-butyltin(rV) oxide and di-n-octyltin oxide, and acyclic and cyclic monoalkyltin (IV) derivatives such as n-butyltin tri-n-butoxide, dialkyltin(IV) dialkoxides such as di-n-butyltin(IV) di-n-butoxide and 2,2-di-n-butyl-2-stanna-l,3-dioxacycloheptane, and trialkyltin alkoxides such as tributyltin ethoxide. See, e.g., U.S. Patent No. 5,348,985 to Pearce et al. [0076] Also, trisstannoxanes having the general formula (I) shown below can be used as a polymerization catalyst to produce branched polyester polymers.

[0077] where R2 is a C1-4 primary alkyl group and R3 is C1-1O alkyl group. [0078] Additionally, organotin compounds with the general formula (II) shown below can be used as a polymerization catalyst to prepare branched polyester polymers from macrocyclic polyester oligomers.

where R3 is defined as above. [0079] As for titanate compounds, tetra(2-ethylhexyl) titanate, tetraisopropyl titanate, tetrabutyl titanate, and titanate compounds with the general formula (III) shown below can be used as polymerization catalysts.

(III) wherein: each R4 is independently an alkyl group, or the two R4 groups taken together form a

divalent aliphatic hydrocarbon group; R5 is a C2-10 divalent or trivalent aliphatic hydrocarbon

group; R6 is a methylene or ethylene group; and n is 0 or 1.

[0080] Typical examples of titanate compounds with the above general formula are shown in

Table 1.

Table 1. Examples of Titanate Compounds Having Formula (III)

Di-I -butyl 2,2-dimethylpropane- Di-I -butyl 2,2-diethylpropane- 1,3-dioxytitanate 1,3-dioxytitanate

Di-I -butyl 2(l-propyl)-2- Di-I -butyl 2-ethylhexane- methylpropane-1 ,3-dioxytitanate 1 ,3-dioxytitanate

Di(2-ethyl- 1 -hexyl) 2,2-dimethylpropane- Di(2-ethyl- 1 -hexyl) 2,2-diethylpropane- 1,3-dioxytitanate 1 ,3-dioxytitanate

Di(2-ethyl- 1 -hexyl) 2-( 1 -propyl)-2- methylpropane-1 ,3-dioxytitanate Di(2-ethyl-l -hexyl) 2-ethylhexane- 1 ,3-dioxytitanate

Di(2-ethyl- 1 -hexyl) 2-( 1 -butyl)-2- ethylpropane- 1 ,3-dioxytitanate [0081] Titanate ester compounds having at least one moiety of the following general formula have also been used as polymerization catalysts:

or

wherein: each R7 is independently a C2-3 alkylene group; R8 is a Ci-6 alkyl group or unsubstituted or substituted phenyl group; Z is O or N; provided when Z is O, m = n = O, and when Z is N, m = O or 1 and m + n = 1 ; each R9 is independently a C2-6 alkylene group; and q is O or l. [0082] Typical examples of such titanate compounds are shown below as formula (VI) and formula (VII):

[0083] Other polymerization catalysts which may be used in the blend materials of the invention include aryl titanates, described, for example, in co-owned U.S. Patent Application No. 10/102,162, published as U.S. Patent Application Publication No. US 2003/0195328, the text of which is incorporated by reference herein in its entirety. Also, polymer-containing organo-metal catalysts may be used in the invention. These include the polymer-containing catalysts described in co-owned U.S. Patent Application No. 10/040,530, published as U.S. Patent Application Publication No. US 2003/0162654, the text of which is incorporated by reference herein in its entirety. III. Preparation of Mixtures Including MPO and Filler [0084] Talc, milled glass fiber, and/or other fillers may be blended with a macrocyclic polyester oligomer (MPO), for example, via melt-mixing, powder mixing, or extrusion. Preferably, the filler is added to MPO before polymerization of the MPO, as this is found to enhance the ultimate dispersion of certain fillers, including anhydrous talc and milled glass fiber, in the polymerized product. In an alternative embodiment, the MPO is partially polymerized at the time of introduction of the filler. [0085] The filler is preferably added to MPO by contacting the filler with molten MPO. Contact of the filler with MPO should take place at a temperature in which all, substantially all, or a significant proportion (for example, more than about 30 wt.%, more than about 60 wt.%, or, preferably, more than about 90 wt.%) of the MPO is melted. In an embodiment where the MPO comprises macrocyclic poly(butylene terephthalate) oligomer in a substantial proportion, filler is preferably added to the MPO when the MPO is at a temperature from about 150°C to about 190°C, for example. Contact of the filler with MPO is preferably combined with mixing, extrusion, or any other process that enhances the dispersion of filler into MPO. The process may be a batch process, or it may be continuous or semi-continuous. In one embodiment, "melt- mixing" occurs as a mixture of MPO and filler is extruded, and the extrudate is quenched. [0086] An appropriate catalyst - for example, a zinc-, titanium-, or tin-containing polymerization catalyst such as those described herein above - may be added before, during, or after the filler is contacted (and preferably mixed) with the macrocyclic oligoester to produce a one-part, ready-to-use material. In one embodiment of the invention, the amount of polymerization catalyst employed is generally an amount from about 0.01 to about 10.0 mole percent, preferably from about 0.1 to about 2 mole percent, and more preferably from about 0.2 to about 0.6 mole percent, based on total moles of repeat units of the MPO. [0087] In an alternative embodiment, the MPO-filler mixture does not contain polymerization catalyst. For example, the MPO-filler mixture may consist essentially of MPO and filler. This type of mixture gives rise to a "two-part" polymerization system, where the polymerization catalyst is provided separately. For example, the filler-MPO mixture can be added to a reaction vessel at a different time, or via a different mechanism, than the polymerization catalyst. In one embodiment, the filler-MPO mixture is extruded or injection-molded together with a separately- provided polymerization catalyst. [0088] The mixtures of the invention may be used in any combination of one or more processes - for example (and without limitation), rotational molding, injection molding, powder coating, compression molding, extrusion, pultrusion, resin film infusion, solvent prepreg, hot melt prepreg, resin transfer molding, filament winding, and roll wrapping processes. Articles produced by these processes are encompassed within the scope of this invention. Examples of these processes are provided in co-owned U.S. Patent No. 6,369,157, by Winckler et al., and co- owned U.S. Patent No. 6,420,047, by Winckler et al., the texts of which are incorporated by reference herein, in their entirety. Depending on the type and proportion of filler, the MPO-filler mixtures of the invention exhibit moderately higher melt viscosities than unfilled MPO. Therefore, these mixtures may be particularly well-suited for use in low-pressure processes such as rotational molding, powder coating, low-pressure molding, gas-assist molding, short-shot molding, co-injection molding, reaction-injection molding, blow molding, thermoforming, and combinations thereof, where a higher melt viscosity is desired. [0089] Examples of MPO-filler mixtures and polymer compositions formed from polymerization of the mixtures are described in the following Experimental Examples section. IV. Experimental Examples [0090] Examples 1-12 illustrate methods of preparing a stable, one-part, ready-to-polymerize, intimate physical mixture comprising an MPO, a filler, and a polymerization catalyst. Properties of the polymer compositions resulting from the polymerization of these mixtures are shown in Tables 2-5 and in Figures 1-3. [0091] Examples 1-12 employ the use of macrocyclic polyester oligomers manufactured by Cyclics Corporation of Schenectady, NY, that are primarily composed of macrocyclic poly(l,4- butylene terephthalate) oligomer. The MPO used in Examples 1-3 is referred to herein as MPO- 2 and contains about 93 mol.% (1,4-butylene terephthalate) units and about 7 mol.% (2,2'- oxydiethylene terephthalate) units. The MPO used in Examples 4-12 is referred to herein as MPO-3 and contains about 100 mol.% (1,4-butylene terephthalate) units. MPO-2 and MPO-3 each contain about 40.2 wt.% dimer species, about 39.0 wt.% trimer species, about 5.5 wt.% tetramer species, about 12.9 wt.% pentamer species, and about 2.4 wt.% higher oligomer species. [0092] In one embodiment of the invention, the MPO of the blend material is a composition comprising from about 30 to about 45 wt.% dimer species, from about 30 to about 45 wt.% trimer species, from about 0 to about 10 wt.% tetramer species, and from about 5 wt.% to about 20 wt.% pentamer species. MPO formulations outside these ranges may be used, as well. Certain embodiments of the invention may include modifying compositions of MPO's. Various methods of modifying compositions of MPO's are described in co-owned U.S. Patent No. 6,436,548, by Phelps, the text of which is incorporated by reference herein in its entirety. Example 1 [0093] A first formulation containing 5 wt.% anhydrous magnesium silicate was prepared by melt-mixing 95.0 grams of MPO-2), 5.0 grams of Ultra Talc 609 (manufactured by Barretts Minerals Inc. of Barretts, MT), and 0.20 grams of stabilizer Irganox 1010 (CAS number 6683- 19-8, manufactured by Ciba-Geigy Corp. of Ardsley, NY). The three components were added in finely pulverized form into a 250-ml, three-neck flask fitted with a vacuum adapter and a magnetic stirrer. The flask was first flushed with argon and then heated under vacuum at 100°C to dry the mixture. After an hour of drying, the flask was heated under vacuum in an oil bath maintained at 1650C. The mixture completely melted within about 30 minutes to form a homogeneous, clear liquid, indicating dissolution of the anhydrous magnesium silicate in the mixture. The flask was then transferred to another oil bath at 150°C, and stirred for 6 minutes as argon gas was introduced into the flask. Butyltin chloride dihydroxide powder (0.371 grams, 0.35 mol.% based on molar amount of total repeat units in MPO-2) was added over a period of about one minute. The resulting mixture was further stirred for an additional 10 minutes and was then poured onto an aluminum plate to quench. Upon cooling to room temperature, the solution became a transparent glass, indicating the silicate particles were dispersed in the mixture well enough to allow light to penetrate the mixture. The resulting tacky solid was annealed in an oven at 80°C under vacuum for 2 hours to allow crystallization. The white solid was pulverized to obtain a one-part, ready-to-polymerize mixture containing 5 wt.% magnesium silicate. Examples 2 and 3 [0094] Second and third formulations containing 10 wt.% and 20 wt.% magnesium silicate, respectively, were prepared following the procedures of Example 1. A control mixture containing no magnesium silicate was also prepared. [0095] The ready-to-polymerize mixtures obtained in Examples 1-3 were polymerized under argon atmosphere by heating at 190°C for 60 minutes in a rectangular mold. The resulting polymers were analyzed by gel permeation chromatography for molecular weight and polymerization conversion. The polymerization rate, ultimate percent conversion, and average polymer molecular weights were not significantly affected by the addition of the silicate. The results, as determined by gel permeation chromatography using polystyrene standards, are shown in Table 2. Table 2. Polymerization of Talc-filled MPO Mixtures

[0096] Shear modulus and Young's modulus were obtained for these samples via ultra-sonic velocity measurement. Specimens for HDT measurement were cut from the control plaque and the plaque containing 10 wt.% talc (Sample 2). HDT measurements were obtained using ASTM method number D608-01 at 66 psi. The results are listed in Table 3, along with the specific gravity of each sample. The results show that specific gravity, shear modulus, and Young's modulus increase according to the amount of filler in the sample. The HDT for the talc- containing sample is significantly higher than the HDT for the control sample. Table 3. Properties of Talc-filled Polymer Compositions

Example 4 [0097] A fourth formulation containing about 10 wt.% magnesium silicate was prepared by melt-mixing 90.0 grams of MPO-3, 10.0 grams of Ultra Talc 609, and 0.20 gram of Irganox 1010 stabilizer. The three components were added in finely-pulverized form into a 250-ml, three neck flask fitted with a vacuum adapter and a magnetic stirrer. The flask was first flushed with argon and then heated under vacuum at 100°C for one hour to dry the mixture. The flask was then heated under vacuum in an oil bath maintained at 1650C. The mixture completely melted within 30 minutes to form a homogeneous, clear liquid. The flask was then transferred to another oil bath at 1500C, and stirred for 6 minutes as argon gas was introduced into the flask. Butyltin chloride dihydroxide powder (0.371 gram, 0.35 mol.% based on molar amount of total repeat units in MPO-3) was added over a period of one minute. The resulting mixture was poured into a rectangular mold and cured at 19O0C for 60 minutes. Samples for dynamic mechanical thermal analysis (DMTA) were cut from the cured plaque. Example 5 [0098] A fifth formulation containing 30 wt.% magnesium silicate was prepared following the procedures of Example 4 using MPO-3. A control mixture containing no magnesium silicate was also prepared. Samples for DMTA testing were cut from cured plaques of both formulations. Examples 6 and 7 [0099] A sixth formulation containing 60 wt.% milled glass fibers (200 micron, unsized, Microglass® 3032 manufactured by Fibertec Inc. of Bridgewater, MA) were prepared according to the procedure described for Example 4 (replacing the Ultra Talc of Example 4 with Microglass® 3032). A seventh formulation containing 30 wt.% milled glass fiber (1/16", sized, manufactured by Fibertec Inc.), and an unfilled control formulation were prepared as well. Samples for use in DMTA testing were cut from cured plaques of each formulation. [00100] Dynamic mechanical thermal analysis (DMTA) was conducted on samples cut from the plaques prepared in Examples 4-7 using a three-point bending mode deformation at a deformation frequency of 10 Hz. The results are shown graphically in Figures 1-3, where the value E' represents storage modulus and "tan d" represents tangent delta (loss tangent), which is a measure of damping performance (ability of a material to dissipate energy). [00101] Figure 1 depicts DMTA results for the polymer compositions of Examples 4 and 5 containing 10 wt.% and 30 wt.% magnesium silicate, respectively, along with the unfilled control. The polymer compositions of Examples 4 and 5 exhibit higher elastic modulus (E1) over a broad temperature range (from about 25°C to about 160°C) than the control sample, indicating grater heat resistance (HDT), improved processibility, increased stiffness, and greater strength due to the presence of the well-dispersed filler in the polymer matrix. There is typically a trade¬ off between E' and hysteresis (as measured by the total area under the tangent delta curve), depending on the total amount of filler used. However, the proportionate increase in E' for the talc-filled polymer compositions of Examples 4 and 5 is significantly greater than the proportionate increase in hysteresis, and the trade-off between E1 and hysteresis may be entirely acceptable for many applications. [00102] Figures 2 and 3 show graphs depicting DMTA results for the polymer compositions of Examples 6 and 7 containing 30 wt.% and 60 wt.% milled glass fiber, respectively, along with the control sample containing no filler. The polymer compositions of Examples 6 and 7 exhibit significantly higher elastic modulus (E1) over a broad temperature range (from about 25°C to about 160°C) than the control sample, indicating grater heat resistance (HDT), improved processibility, increased stiffness, and greater strength due to the presence of the well-dispersed filler in the polymer compositions. Figure 3 indicates the filled polymer compositions of Examples 6 and 7 have a lower tangent delta than the unfilled control sample over a significant portion of the temperature range tested. A lower tangent delta generally indicates higher resilience and lower hysteresis. Examples 8, 9, and 10 [00103] Three different formulations containing 60 wt.% glass spheres (glass spheres with untreated surfaces, having average diameter of 0.1 - 0.2 mm and bulk density of 1.6 g/cm3), 60 wt.% unsized milled glass fiber (Microglass® 3032, manufactured by Fibertec Inc. of Bridgewater, MA), and 60 wt.% sand (Quickrete Commercial Grade Fine Sand, Product No. 1961-52, manufactured by Quikrete Company of Atlanta, GA), respectively, were prepared according to the procedure described for Example 4 (replacing the Ultra Talc of Example 4 with the respective fillers above, and using MPO-3 as the MPO). Flexural strength tests (ISO 178 standard test method) and impact strength tests (Charpy impact strength) were conducted on samples cut from plaques of the formulations containing glass spheres, glass fiber, and sand, respectively (Examples 8-10). The results are summarized in Table 4. The milled-glass-fϊlled sample shows significantly greater strength than the other filled samples. The milled glass filler has a higher aspect ratio than the sand and glass spheres. Table 4. Effects of Filler Type in Polymerized MPO-3 on Flexural and Impact Strength (60 wt.% filler)

Examples 11 and 12 [00104] A 100-mm diameter cylindrical mold was fitted with a 44-mm steel core positioned along the center axis. Two separate parts were molded by polymerizing MPO-3 filled with 15 wt.% talc (Ultra Talc 609 manufactured by Barretts Minerals Inc. of Barretts, MT) and 60 wt.% milled glass fiber (Microglass® 3032, manufactured by Fibertec Inc. of Bridgewater, MA), respectively. In addition, two "control" parts were molded — one control part made by polymerizing a mixture of MPO-3 with 5 wt.% polycaprolactone (Tone™ P-767, manufactured by Dow Chemical Company of Midland, MI) and a second control part made by polymerizing unfilled MPO-3. [00105] The mixtures of MPO-3, polymerization catalyst, and (where applicable) filler were prepared according to the procedure described in Example 4 (substituting the appropriate filler), except that the MPO-3 mixtures were melted at about 170°C and the time from introduction of the catalyst into the mixture until transfer of the mixture into the mold was about 90 seconds. In each experiment, a vacuum of about 10 mm Hg was maintained in the mold during resin transfer, and the mold was cured at about 240°C for about 90 minutes. The mold was removed to an ambient temperature environment, and quench cooled with water spray and application of a wet towel. [00106] The parts made with 15 wt.% talc, 60 wt.% milled glass fiber, and 5 wt.% polycaprolactone (an anti-cracking agent), respectively, had no apparent cracks on their surfaces. Conversely, the part made by polymerizing unfilled MPO-3 had visible surface cracks. Thus, use of talc and/or milled glass that is well-dispersed in MPO-3 according to embodiments of the invention can serve to prevent or reduce cracking on the surface of molded parts. [00107] A Shore durometer test was conducted on the parts made with 15 wt.% talc, 60 wt.% milled glass fiber, and 5 wt.% polycaprolactone, respectively. In accordance with the DMTA modulus data in Figures 1 and 2, the durometer Shore D hardness value was highest for the milled-glass-filled MPO-3 part, followed by the part filled with talc, and the polycaprolactone- filled part had the lowest hardness value. Table 5 summarizes the results of the Shore durometer tests. Table 5. Durometer Shore D Hardness of Three Different Cast Roller Parts.

Equivalents [00108] While the invention has been particularly shown and described with reference to specific preferred embodiments, it should be understood by those skilled in the art that various changes in form and detail may be made therein without departing from the spirit and scope of the invention as defined by the appended claims. [00109] What is claimed is: