Patent Description:
Recently, there has been an increased focus on obtaining polymeric materials derived from renewable resources. This growing trend is aiming at finding replacements to fossil-based resources and materials such as poly(ethylene terephthalate), PET, a high performance plastic that is especially prevalent in packaging due to its gas barrier properties, transparency, and mechanical strength.

Biomass offers a promising renewable alternative to fossil resources, as production of chemicals and materials can be achieved in a carbon-neutral way. In particular, furans are bio-based platform-chemicals, which are easily prepared from plant-based biomasses. Moreover, furans have long been studied as potential precursors for various types of polymers such as thermosets and thermoplastics. More recently, polyesters have become a particularly prominent area of research.

As simple dehydration products of monosaccharides, furans are key bio-based aromatic chemicals with various uses. Moreover, furan-based polyesters, in particular poly(ethylene furanoate) (PEF), possess advantageous material properties. PEF is known to have low oxygen and carbon dioxide permeability, even when compared to PET, a well-known packaging polyester. Reduced permeability to various gases can lead to higher performance packaging.

<NUM>,<NUM>'-Bifuran-<NUM>,<NUM>'-dicarboxylic acid (BFDCA) has recently been described as another furan-based precursor for novel bio-based polyesters (Kainulainen et al. , <NUM>, Miyagawa et al, <NUM>). As a furan "dimer", BFDCA consists fully of bio-based carbon. It has been shown that BFDCA-based homopolyesters, e.g. poly(ethylene bifuranoate) (PEBf), have relatively high glass-transition temperatures, and that the highly conjugated molecular structure of the bifuran monomer provides inherent ultraviolet (UV) light absorption. In addition, it was shown that PEBf possesses lower O<NUM> and water vapor permeability than PET.

<NPL>) discloses the synthesis of bifuran polyesters using a bifuran carboxylic monomer.

<CIT> discloses a process comprising polymerizing a <NUM>,<NUM>'-di(protected)-<NUM>,<NUM>'-bifuran in one or more steps to form a polyester comprising (<NUM>,<NUM>'-bifuran)-<NUM>,<NUM>'-dicarboxylate structural units.

In the present invention, the synthesis of new random copolyesters comprising BFDCA structures is presented. Thermal and mechanical properties of the copolyesters are then compared to the pure homopolyesters.

The present invention is based on a discovery that, surprisingly, the UV light absorption property provided by BFDCA structures for the homopolyester retains in a mixed copolyester even in the case when the copolymer comprises a relatively low number of BFDCA structures. UV-protecting plastics or coatings are useful in food packages and, e.g., in photovoltaic cells, as organic solar cells can retain more of their efficiency over time when properly protected from UV radiation. Further, the novel copolyesters are also promising oxygen and water barrier materials.

The present invention is characterized by what is stated in the appended claims.

Accordingly, the present invention provides a copolyester comprising repeating units of (i) a <NUM>,<NUM>'-bifuran-<NUM>,<NUM>'-dicarboxylic monomer residue, (ii) a diol monomer residue, and (iii) an aliphatic or cycloaliphatic C<NUM>-C<NUM> dicarboxylic monomer residue or an aromatic C<NUM>-C<NUM> dicarboxylic monomer residue, wherein said <NUM>,<NUM>'-bifuran-<NUM>,<NUM>'-dicarboxylic monomer residue is derived from the compound of Formula
<CHM>
wherein R<NUM> and R<NUM> are each independently selected from the group consisting of: -H, -CH<NUM>, -CH<NUM>CH<NUM>, -(CH<NUM>)<NUM>CH<NUM>, -CH(CH<NUM>)<NUM>, -(CH<NUM>)<NUM>CH<NUM>, -(CH<NUM>)<NUM>OH, -(CH<NUM>)<NUM>OH, -(CH<NUM>)<NUM>OH, -(CH<NUM>)<NUM>OH, -(CH<NUM>)<NUM>OH, -(CH<NUM>)<NUM>OH, -(CH<NUM>)<NUM>OH, and
<CHM>
wherein said aliphatic or cycloaliphatic C<NUM>-C<NUM> dicarboxylic monomer residue or said aromatic C<NUM>-C<NUM> dicarboxylic monomer residue is derived from the compound of Formula
<CHM>
wherein R<NUM> and R<NUM> are independently as defined above for Formula (I) and R<NUM> is selected from the group consisting of
<CHM>
<CHM>.

In another aspect, the present invention provides a method of preparing a bifuran copolyester, the method comprising the steps of:.

In a further aspect, the present invention is directed to a use of a <NUM>,<NUM>'-bifuran-<NUM>,<NUM>'-dicarboxylic monomer in preparing copolyesters having ultraviolet light (UV) blocking properties.

The term "polyester" as used herein is inclusive of polymers prepared from multiple monomers that are referred to herein as copolyesters. Terms such as "polymer" and "polyester" are used herein in a broad sense to refer to materials characterized by repeating moieties or units. The polyesters as described herein may have desirable physical and thermal properties and can be used to partially or wholly replace polyesters derived from fossil resources, such as poly(ethylene terephthalate), PET.

In the context of the present specification, ester monomers preferably comprise the general formula R'OOCRCOOR", where R may be an alkyl group, or an aryl group, and R' and R" may be an alkyl group or an aryl group. Dashed lines in the structure formulas presented herein represent the linkage between a C atom and an O atom or between a C atom and another C atom (such as linkages selected from the group consisting of C-R, R-C, R'-O and O-R" in the formula R'OOCRCOOR'').

In various aspects described herein, polyesters can be prepared from biomass by utilizing monomers which are obtained from biomass. Furfural and hydroxymethylfurfural (HMF) may be obtained from pentoses and hexoses, respectively. HMF can also be oxidized or reduced to obtain <NUM>,<NUM>-furandicarboxylic acid (FDCA). The preparation of dimethyl <NUM>,<NUM>-furandicarboxylate and dimethyl <NUM>,<NUM>'-bifuran-<NUM>,<NUM>'-dicarboxylate are described in the Experimental Section below.

In general, polyesters are prepared by reacting a dicarboxylic monomer containing furan and/or other aromatic functionality, and at least one diol. Suitable diols include aliphatic or cycloaliphatic C3-C10 diols, non-limiting examples of which include <NUM>,<NUM>-propanediol, <NUM>,<NUM>-butanediol, and <NUM>,<NUM>-ethanediol.

Unless otherwise clear from context, percentages referred to herein are expressed as percent by weight based on the total composition weight.

The present invention is directed to a copolyester comprising repeating units of (i) a <NUM>,<NUM>'-bifuran-<NUM>,<NUM>'-dicarboxylic monomer residue, (ii) a diol monomer residue, and (iii) an aliphatic or cycloaliphatic C<NUM>-C<NUM> dicarboxylic monomer residue or an aromatic C<NUM>-C<NUM> dicarboxylic monomer residue, wherein said <NUM>,<NUM>'-bifuran-<NUM>,<NUM>'-dicarboxylic monomer residue is derived from the compound of Formula
<CHM>
wherein R<NUM> and R<NUM> are each independently selected from the group consisting of: -H, -CH<NUM>, -CH<NUM>CH<NUM>, -(CH<NUM>)<NUM>CH<NUM>, -CH(CH<NUM>)<NUM>, -(CH<NUM>)<NUM>CH<NUM>, -(CH<NUM>)<NUM>OH, -(CH<NUM>)<NUM>OH, -(CH<NUM>)<NUM>OH, -(CH<NUM>)<NUM>OH, -(CH<NUM>)<NUM>OH, -(CH<NUM>)<NUM>OH, -(CH<NUM>)<NUM>OH, and
<CHM>
wherein said aliphatic or cycloaliphatic C<NUM>-C<NUM> dicarboxylic monomer residue or said aromatic C<NUM>-C<NUM> dicarboxylic monomer residue is derived from the compound of Formula
<CHM>
wherein R<NUM> and R<NUM> are independently as defined above for Formula (I) and R<NUM> is selected from the group consisting of
<CHM>
<CHM>
Preferably, the molar ratio of (i) the <NUM>,<NUM>'-bifuran-<NUM>,<NUM>'-dicarboxylic residues and (iii) the aliphatic or cycloaliphatic C<NUM>-C<NUM> dicarboxylic residues or the aromatic C<NUM>-C<NUM> dicarboxylic residues is between <NUM>:<NUM> and <NUM>:<NUM> in said copolyester. More preferably, said ratio is <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM> or any range between the listed ratios. Most preferably, said range is between <NUM>:<NUM> and <NUM>:<NUM>, between <NUM>:<NUM> and <NUM>:<NUM>, between <NUM>:<NUM> and <NUM>:<NUM>, <NUM>:<NUM> or <NUM>:<NUM>.

The dicarboxylic monomer residues of the copolyester are preferably derived or obtained from the diesters of said monomers. An example of an diester of the aromatic C<NUM> dicarboxylic monomer residue is dimethyl <NUM>,<NUM>-furandicarboxylate, FDCA (see Experimental Section below). An example of an diester of the aromatic C<NUM> dicarboxylic monomer residue is dimethyl terephthalate (DMT):
<CHM>.

In another preferred embodiment, the present invention is directed to a bifuran copolyester comprising the structure of Formula
<CHM>
wherein R<NUM> is selected from the group consisting of
<CHM>
<CHM>
wherein each R<NUM> is independently selected from the group consisting of -CH<NUM>-, -(CH<NUM>)<NUM>-, -(CH<NUM>)<NUM>-, -(CH<NUM>)<NUM>-, -(CH<NUM>)<NUM>-, -(CH<NUM>)<NUM>-, -(CH<NUM>)<NUM>-, -(CH<NUM>)<NUM>-, and
<CHM>
wherein the two structures in parenthesis represent randomly repeating units or residues of the copolyester, and wherein x is independently an integer of <NUM> or more, preferably <NUM>-<NUM>, and y is independently an integer of <NUM> or more, preferably <NUM>-<NUM>. Preferably, the ratio of x:y is between <NUM>:<NUM> and <NUM>:<NUM>. More preferably, said ratio is <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM> or any range between the listed ratios. Most preferably, said range is between <NUM>:<NUM> and <NUM>:<NUM>, between <NUM>:<NUM> and <NUM>:<NUM>, between <NUM>:<NUM> and <NUM>:<NUM>, <NUM>:<NUM> or <NUM>:<NUM>.

In another preferred embodiment, R<NUM> is selected from the group consisting of:
<CHM>.

In a more preferred embodiment, R<NUM> is
<CHM>.

In another preferred embodiment, each R<NUM> is -(CH<NUM>)<NUM>-.

Having similar or better properties compared to PET (see Experimental Section below), a person skilled in the art would understand that the above described copolyester can be applied to beverage bottles, food package films, shopping bags and other food package containers.

The present invention is further directed to a method of preparing a bifuran copolyester, the method comprising the steps of:.

A typically useful procedure is thus a conventional two-step melt-polymerization method, such as generally also used in the production of PET. Thereby a mixture of the diol and dicarboxylic monomers are subjected to heating, in two stages. Thus, e.g., the mixture is first exposed to a temperature in the range of <NUM> - <NUM>, and thereafter to a temperature of <NUM> - <NUM>. Vacuum may be applied gradually, to obtain high molecular weight polyesters. Typically, the pressure applied during step c) is subatmospheric, for example <NUM> to <NUM> mBar (<NUM> to <NUM> Pa), for example about <NUM> to <NUM> mBar (<NUM> to <NUM> Pa).

In a preferred embodiment, said metal catalyst in step a) comprises at least one titanium, bismuth, zirconium, tin, antimony, germanium, aluminium, cobalt, magnesium, or manganese compound. More preferably said metal catalyst is tetrabutyl titanate (titanium (IV) butoxide).

Accordingly, in embodiments of the invention, at least one metal catalyst is present in steps a) and b). The amount of metal in the metal catalyst is in the range of from <NUM> parts per million (ppm, i.e. mg/kg) to <NUM> ppm by weight, based on a theoretical yield of <NUM>% of the polymer produced. In one embodiment, the metal catalyst is present in the mixture in a concentration in the range of from about <NUM> ppm (mg/kg) to about <NUM> ppm, based on the total weight of the polymer. Suitable metal catalysts can include, for example, titanium compounds, bismuth compounds such as bismuth oxide, germanium compounds such as germanium dioxide, zirconium compounds such as tetraalkyl zirconates, tin compounds such as butyl stannoic acid, tin oxides and alkyl tins, antimony compounds such as antimony trioxide and antimony triacetate, aluminum compounds such as aluminum carboxylates and alkoxides, inorganic acid salts of aluminum, cobalt compounds such as cobalt acetate, manganese compounds such as manganese acetate, or a combination thereof. Alternatively, the catalyst can be a tetraalkyl titanate Ti(OR)<NUM>, for example tetraisopropyl titanate, tetrabutyl titanate (tetra-n-butyl titanate), tetrakis(<NUM>-ethylhexyl) titanate, titanium chelates such as, acetylacetonate titanate, ethyl acetoacetate titanate, triethanolamine titanate, lactic acid titanate, or a combination thereof. In one embodiment, the metal catalyst comprises at least one titanium, bismuth, zirconium, tin, antimony, germanium, aluminum, cobalt, magnesium, or manganese compound. In one embodiment, the metal catalyst comprises at least one titanium compound. Suitable metal catalysts can be obtained commercially or prepared by known methods.

In preferred embodiments, said bifuran of Formula (I) in step a) is dimethyl <NUM>,<NUM>'-bifuran-<NUM>,<NUM>'-dicarboxylate having the structure
<CHM>.

In other preferred embodiments, said diester compound in step a) is dimethyl <NUM>,<NUM>-furandicarboxylate having the structure
<CHM>.

In other preferred embodiments, said aliphatic C<NUM>-C<NUM> diol is <NUM>,<NUM>-butanediol having the structure
<CHM>.

In particularly preferred embodiments, the molar ratio of compounds (i) and (ii) in step a) is between <NUM>:<NUM> and <NUM>:<NUM>. More preferably, said ratio is <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM>, <NUM>:<NUM> or any range between the listed ratios. Most preferably, said range is between <NUM>:<NUM> and <NUM>:<NUM>, between <NUM>:<NUM> and <NUM>:<NUM>, between <NUM>:<NUM> and <NUM>:<NUM>, <NUM>:<NUM> or <NUM>:<NUM>.

In one embodiment, in step b) of the process a mixture comprising a bifuran of Formula (I), a diester compound of Formula (II), a diol selected from the group consisting of ethylene glycol, <NUM>,<NUM>-propanediol, <NUM>,<NUM>-butanediol, <NUM>,<NUM>-cyclohexanedimethanol, or mixtures thereof, and a metal catalyst is contacted at a temperature in the range of from <NUM> to <NUM> to form a prepolymer.

In the methods disclosed herein, the step b) is preferably performed at a temperature in the range of from <NUM> to <NUM>, for example in the range of from <NUM> to <NUM> or from <NUM> to <NUM> or from <NUM> to <NUM> or from <NUM> to <NUM>. The time is typically from one hour to several hours, for example <NUM>, <NUM>, <NUM>, or <NUM> hours or any time in between <NUM> hour and <NUM> hours.

In the preferred methods disclosed herein, polycondensation in step c) is performed by heating the prepolymer obtained in step b) under reduced pressure to a temperature in the range of from <NUM> to <NUM> to form the bifuran copolyester. A different catalyst, or more of the same catalyst as used in step b), can be added in step c). The temperature in step c) is typically in the range of from <NUM> to <NUM>, for example from <NUM> to <NUM> or from <NUM> to <NUM>. The pressure can be from less than about one atmosphere to <NUM> atmospheres. In this step, the prepolymer undergoes polycondensation reactions, increasing the molecular weight of the polymer, and the diol is distilled off. The polycondensation step can be continued at a temperature in the range of from <NUM> to <NUM> for such a time as the intrinsic viscosity of the polymer reaches at least about <NUM> dL/g. The time is typically from <NUM> hour to several hours, for example <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM> or <NUM> hours or any time in between <NUM> hour and <NUM> hours. In one embodiment, the polymer obtained from step c) has an intrinsic viscosity of at least <NUM> dL/g. Once the desired intrinsic viscosity of the polymer is reached, the reactor and its contents can be cooled, for example to room temperature, to obtain the bifuran copolyester.

The present invention is also directed to use of a <NUM>,<NUM>'-bifuran-<NUM>,<NUM>'-dicarboxylic monomer in preparing copolyesters having ultraviolet light (UV) blocking properties. Preferably, said <NUM>,<NUM>'-bifuran-<NUM>,<NUM>'-dicarboxylic monomer is a diester of the <NUM>,<NUM>'-bifuran-<NUM>,<NUM>'-dicarboxylic monomer, such as dimethyl <NUM>,<NUM>'-bifuran-<NUM>,<NUM>'-dicarboxylate. Preferably, the prepared copolyester contains <NUM>-<NUM>% of <NUM>,<NUM>'-bifuran-<NUM>,<NUM>'-dicarboxylic monomer residues.

Commercial grade solvents and reagents were used as received unless otherwise noted.

Dimethyl <NUM>,<NUM>-furandicarboxylate, FDCA (<NUM>): <NUM>,<NUM>-Furandicarboxylic acid (<NUM>) was mixed with dry methanol (<NUM>), and <NUM>% sulfuric acid (<NUM> equiv) was added into the mixture. After refluxing overnight, the cooled mixture was evaporated to about <NUM>/<NUM> volume. After dilution with deionized water, the precipitated diester was filtered onto paper. After drying in air, the raw product was dissolved in ethyl acetate and filtered through silica gel. After evaporation, dimethyl <NUM>,<NUM>-furandicarboxylate was afforded (<NUM>, <NUM>%). <NUM>H NMR (<NUM>, CDCl<NUM>, ppm): δ <NUM> (s, <NUM>), <NUM> (s, <NUM>).

Dimethyl <NUM>,<NUM>'-bifuran-<NUM>,<NUM>'-dicarboxylate, BFDCA (<NUM>): The synthesis method reported previously was followed to afford dimethyl <NUM>,<NUM>'-bifuran-<NUM>,<NUM>'-dicarboxylate (<NUM>, <NUM>%) as small white needles (Kainulainen et al. <NUM>H NMR (<NUM>, CDCl<NUM>, ppm): δ <NUM> (d, <NUM>, J = <NUM>), <NUM> (d, <NUM>, J = <NUM>), <NUM> (s, <NUM>).

Polyester synthesis: The polyesters were synthesized by weighing the diester(s) <NUM> and <NUM> in an appropriate ratio into a round-bottom flask equipped with a magnetic stirring bar. Dry <NUM>,<NUM>-butanediol was added, together with tetrabutyl titanate (<NUM> mol% relative to the total diester amount). The flask was heated to <NUM> under argon to initiate the reaction. After <NUM> reaction, the pressure was gradually lowered to <NUM> mbar (<NUM> Pa) over the period of <NUM>. After increasing the temperature to <NUM>, the reaction was allowed to continue for <NUM>. The cooled, solid polyester was allowed to dissolve in a mixture of CF<NUM>COOH and CHCl<NUM>. The polyester was precipitated into methanol, affording a fibrous solid. The polyester was dried under vacuum at <NUM>. For NMR measurements, a polyester sample was dissolved in CF<NUM>COOD.

Dilute solution viscometry: Intrinsic viscosities were evaluated using flow-times measured with a micro-Ubbelohde viscometer <NUM>. Polyester samples were dissolved in CF<NUM>COOH, and the solution filtered to prepare <NUM>/dL solutions for measurements.

Differential scanning calorimetry (DSC): Differential scanning calorimeter (Mettler Toledo DSC 821e) with heating and cooling rates of <NUM>/min and nitrogen gas flow of <NUM><NUM>/min was used. <NUM> samples placed in sealed <NUM>µL Al pans were used for the measurements.

Thermogravimetric analysis: Thermogravimetric analyzer (Mettler-Toledo TGA851e) with nitrogen flow of <NUM><NUM>/min was run from <NUM> to <NUM> at a heating rate of <NUM>/min.

Melt pressing: Dry polyester was melted at the appropriate temperature inside a closed heat-press, and the melt was then pressed into a film between two polyimide-coated aluminium plates. After cooling, a transparent film was obtained.

Tensile testing: Rectangular tensile test specimens were cut from the films, and the specimens were allowed to stand for <NUM>-<NUM> weeks prior to the tensile tests conducted at <NUM>. Tensile tester (Instron <NUM>, USA) with a gage length of <NUM> and crosshead speed of <NUM>/min was used to characterize the tensile modulus, tensile strength and elongation at break.

UV-Vis: Spectrophotometer (Shimadzu UV-<NUM>) was used to characterize the absorption and transmittance of the melt-pressed films.

Dimethyl esters of FDCA (<NUM>), BFDCA (<NUM>) and <NUM>,<NUM>-butanediol were polymerized in accordance with Table <NUM>.

Using the appropriate feed ratio of <NUM> and <NUM>, the desired polyesters were prepared in the presence of catalytic tetrabutyl titanate (TBT). The purity and structure of the polyesters were confirmed with <NUM>H NMR analysis (<FIG>). Diester feed ratios were practically identical to the ratios observed in the actual products. This suggests that both <NUM> and <NUM> are suitably stable and reactive monomers in polycondensation reactions.

<NUM>H and <NUM>C NMR analysis also confirms the random distribution of furan and bifuran units in the polyester chains. Specifically, assignment of the chain structure was obtained (<FIG>, Table <NUM>) from Equations <NUM> and <NUM> by using areas under the corresponding peaks (AFF, ABB, AFB, and ABF) in the <NUM>C NMR spectrum. Calculating the randomness indices (Ri, Equation <NUM>) using the values from Equations <NUM> and <NUM>, a highly random distribution of both furan-based moieties can be discerned. <MAT> <MAT> <MAT>.

The thermal properties were characterized using DSC. Slow <NUM>/min scanning rate reveals that PBF and PBBf are typical semi-crystalline materials, having clear cold-crystallization and melting peaks (<FIG>). The thermal properties of both PBF and PBBf correspond to previously reported values, though Tg was not previously reported for PBBf (Miyagawa et al. At even slower scanning rate (<NUM>/min), the semi-crystalline nature of PBF<NUM>Bf<NUM> and PBF<NUM>Bf<NUM> becomes evident (<FIG>). The data point to the fact that higher comonomer incorporation hinders crystallization. When the comonomer content approaches equimolar ratio, e.g. in PBF<NUM>Bf<NUM>, PBF<NUM>Bf<NUM>, and PBF<NUM>Bf<NUM>, highly amorphous copolyesters are obtained. The impact on crystallinity is lessened if the content of defects resulting from the incorporation of the minor comonomer is kept relatively small, e.g. below <NUM> mol%. However, high bifuran content increases the stiffness of the polyester chains, resulting in higher Tg.

Thermogravimetric analysis shows that the thermal stabilities (Table <NUM> and <FIG>) are comparable to existing polyester-type materials, i.e. each composition underwent a single decomposition step at <NUM>-<NUM>. These values are highly comparable to PET and PBT, and especially PEF. However, the more highly aromatic bifuran structure leads to an increase in the char yield. In conclusion, it should be recognized that the gap between decomposition and processing temperatures is wide for these materials.

All copolyesters had excellent mechanical properties, most notably exceeding the performance of PBF, with tensile strengths of ≥<NUM> MPa. The tensile moduli were practically unchanged across the series.

The most notable effect provided by the bifuran moieties is their inherent UV absorbance. The copolyesters functioned as effective UV light filters up to <NUM> wavelengths (<FIG>), irrespective of the bifuran content at the prepared thickness (<NUM>-<NUM>). It is particularly notable that PBF does not provide similar UV light absorption at <NUM>-<NUM>. Thus, the copolyester films are promising transparent bio-based materials with low UV transmittance, as the visible light transmittance was excellent (e.g. <NUM>% at <NUM>). While it is known (Kainulainen et al. , <NUM>, and Miyagawa et al. , <NUM>), that monomer <NUM> has its absorption maximum at longer wavelength (<NUM>) than monomer <NUM> (<NUM>) in solution, the bifuran moieties can provide surprisingly significant UV absorbance up to almost <NUM>. In contrast, PBF decreases in absorbance rapidly at wavelengths longer than <NUM>.

Claim 1:
A copolyester comprising repeating units of (i) a <NUM>,<NUM>'-bifuran-<NUM>,<NUM>'-dicarboxylic monomer residue, (ii) a diol monomer residue, and (iii) an aliphatic or cycloaliphatic C<NUM>-C<NUM> dicarboxylic monomer residue or an aromatic C<NUM>-C<NUM> dicarboxylic monomer residue, wherein said <NUM>,<NUM>'-bifuran-<NUM>,<NUM>'-dicarboxylic monomer residue is derived from the compound of Formula
<CHM>
wherein R<NUM> and R<NUM> are each independently selected from the group consisting of: -H, -CH<NUM>, -CH<NUM>CH<NUM>, -(CH<NUM>)<NUM>CH<NUM>, -CH(CH<NUM>)<NUM>, -(CH<NUM>)<NUM>CH<NUM>, -(CH<NUM>)<NUM>OH, -(CH<NUM>)<NUM>OH, -(CH<NUM>)<NUM>OH, -(CH<NUM>)<NUM>OH, -(CH<NUM>)<NUM>OH, -(CH<NUM>)<NUM>OH, -(CH<NUM>)<NUM>OH, and
<CHM>
wherein said aliphatic or cycloaliphatic C<NUM>-C<NUM> dicarboxylic monomer residue or said aromatic C<NUM>-C<NUM> dicarboxylic monomer residue is derived from the compound of Formula
<CHM>
wherein R<NUM> and R<NUM> are independently as defined above for Formula (I) and R<NUM> is selected from the group consisting of
<CHM>
<CHM>