AND CYCLIC ANHYDRIDES

FIELD OF THE INVENTION This invention concerns a process for the copolymerization of tetrahydrofurans with cyclic carboxylic anhydrides to form a poly(ester-ether) , wherein the polymerization is catalyzed by selected metal perfluoroalkylsulfonates. BACKGROUND

Copolymers of tetrahydrofuran and cyclic anhydrides are known in the art . These polymers were made with the use of a Lewis acid catalyst such as an organoaluminum compound or an onium compound, optionally in the presence of a cocatalyst, see for example J. Habermeier, et al., J. Polym. Sci., Part C, p. 2131-2141 (1967) . No mention is made in this paper of metal perfluoroalkyl- sulfonates as catalysts.

S. L. Borkowsky, et al. , Organometal. , vol. 10, p. 1268-1274 (1991) report that certain zirconium complexes can initiate the polymerization of tetrahydro¬ furan. No mention is made of zirconium perfluoroalkyl¬ sulfonates, or of copolymers.

U.S. Patent 3,842,019 describes the polymerization of oxiranes and other small ring compounds by a presumed cationic mechanism, using as the catalyst the decomposition products of metal perfluoroalkyl- sulfonates . These catalysts are described as "latent", that is no reaction occurs until the metal salt is decomposed. The reactions reported are relatively slow, even at elevated temperatures.

U.S. Patents 5,084,586 and 5,124,417 describe the cationic polymerization of various monomers, including cyclic ethers, using onium cations, whose corresponding anions are fluororalkylsulfatometallates. Onium ion

catalyzed cationic polymerizations are well known, and there is no mention in these patents of the use of metal salts not containing onium ions, such as metal triflates, as catalysts for the polymerization of cyclic ethers.

German Patent Application 2,459,163 describes the polymerization of THF using a combination of ferric chloride and carboxylic anhydride as catalyst .

G. A. Olah, et al., J. Appl . Polym. Sci . , Vol. 45, 1355-1360 (1992) describe the use of boron, aluminum and gallium tristriflate to catalyze the polymerization of THF.

SUMMARY OF THE INVENTION

This invention concerns a process for the production of a poly(ester-ether) , comprising, contacting one or more cyclic carboxylic anhydrides, one or more tetrahydrofurans, and a catalyst of the formula MZg-Q _t , and an accelerator selected from the group consisting of carboxylic acids whose pKa in water is less than 6, carboxylic anhydrides and acyl halides, wherein:

M is a metal selected from the group consisting of cobalt, vanadium, niobium, tungsten, strontium, barium, scandium, yttrium, the rare earth metals, titanium, zirconium, hafnium, chromium, molybdenum, tantalum, rhenium, iron, ruthenium, osmium, rhodium, iridium, palladium, platinum, silver, gold, zinc, cadmium, mercury, aluminum, gallium, indium, thulium, germanium, tin, lead, arsenic, antimony and bismuth; at least one of Z is an anion of the formula "OSO2R ⁵ , wherein R ⁵ is perfluoroalkyl containing 1 to 12 carbon atoms or part of a fluorinated polymer wherein the carbon atoms alpha and beta to the sulfonate group are together bonded to at least four fluorine atoms, or

tetraphenylborate, and the remainder of Z is oxo or one or more monovalent anions; s is 2 when M is strontium, barium, cobalt, rhodium, iridium, palladium, platinum, chromium, zinc, cadmium or mercury; s is 3 when M is scandium, yttrium, a rare earth metal, arsenic, antimony, bismuth, gold, iron, ruthenium, osmium, aluminum, gallium, indium or thulium; s is 4 when M is titanium, zirconium, hafnium, molybdenum, germanium, tin, or lead; s is 5 when M is rhenium, vanadium, niobium or tantalum; s is 6 when M is tungsten; Q is a neutral ligand; t is 0 or an integer of 1 to 6; and provided that each oxo group present counts as two of s .

DETAILS OF THE INVENTION

In the instant process a tetrahydrofuran is copolymerized with a cyclic anhydride to yield a poly(ether-ester) . By a tetrahydrofuran (THF) is meant the common meaning, a compound containing a saturated five membered ring in which one of the ring atoms is oxygen and the other four ring atoms are carbon. Preferred tetrahydrofurans have the formula

wherein each R ¹ , R ² , R ³ and R ⁴ is independently hydrogen or hydrocarbyl containing 1 to 20 carbon atoms. In especially preferred THFs, R ¹ , one of R ² and all of R ³

and R ⁴ are hydrogen, and the remaining R ² is alkyl containing 1-4 carbon atoms, particularly the remaining R ² is methyl . In another especially preferred embodiment all of R ¹ , R ² , R ³ and R ⁴ are hydrogen. ^'

By a cyclic carboxylic anhydride is meant the common meaning, a compound that can be represented by the formula

wherein E is a divalent organic radical which is bound to each valence of the carboxylic anhydride group through a carbon atom. In preferred embodiments, E is n-alkylene containing 1 to 4 carbon atoms or alkyl substituted n-alkylene wherein the n-alkylene group contains 1 to 4 carbon atoms, and E contains a total of 2 to 20 carbon atoms. Specific useful cyclic carboxylic anhydrides include, but are not limited to, succinic, maleic, phthalic, 5-methyl-5-nobornene- dicarboxylic acid and 1,2-cyclohexanedicarboxylic acid anhydrides. Preferred cyclic carboxylic anhydrides include maleic, succinic, phthalic and 1, 2-cyclohexane- dicarboxylic acid anhydrides .

In the above formula E may be substituted with one or more additional carboxylic anhydride groupings. For instance, 1,2, 4, 5-benzenetetracarboxylic dianhydride may be used in the process. It is believed that, depending on the concentration of the dianhydride, the resulting copolymer may be branched or even crosslinked (higher dianhydride levels) .

It is believed that monovalent anions that are relatively nonnucleophilic are useful as Z. Examples of

such anions are tetraphneylborate, "OSO ₂ R ⁵ , wherein R ⁵ is perfluoroalkyl or wherein R ⁵ is part of a fluorinated polymer wherein the carbon atoms alpha and beta to the sulfonate group are together bonded to at least 4 fluorine atoms (as in -CF ₂ CF2O ₂ SO-) . It is preferred if R ⁵ is perfluoroalkyl, and particularly preferred if R ⁵ is trifluoromethyl, so that "OSO2R ⁵ is trifluoromethane- sulfonate, herein also called triflate.

The catalyst may be yttrium or rare earth compound of the formula MZ3 where M is a trivalent ion of yttrium, or one of the rare earths, lanthanum, cerium, praeseodymium, neodymium, promethium, samarium, europium, gadolinium, terbium, dysprosium, holmium, erbium, thulium, ytterbium, and lutetium. Preferred metals, M, are strontium, scandium yttrium, the rare earth metals, titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, rhenium, iron, ruthenium, palladium, copper, gold, zinc, tin and bismuth. More preferred metals are yttrium, the rare earth metals, and scandium. Especially preferred metals are yttrium, ytterbium, dysprosium, erbium, neodymium, lanthanum, and scandium. Another preferred metal is "mischmetall" (sometimes also called "didymium"), which is a mixture of rare earth metals as obtained from the ore. It is believed monovalent anions that are relatively nonnucleophilic are useful as Z . Examples of such anions are tetraphenylborate, "OSO2R ⁵ , wherein R ⁵ is perfluoroalkyl, or wherein R ⁵ is part of a fluorinated polymer wherein the carbon atoms alpha and beta to a sulfonate group are together bonded to at least 4 fluorine atoms (as in -CF2CF2OSO2-) . It is preferred if R ⁵ is perfluoroalkyl. In a particularly preferred R ⁵ is trifluoromethyl, and the anion is herein called "triflate".

Generally speaking, any metallic compound in which the correct metal in the correct oxidation state (see above) is present and bonded to a triflate or similar anion will be a catalyst. Such a compound must of course be reasonably stable during the polymerization (or depolymerization, see below) , or decompose to another compound which is still a triflate (or similar anion) compound of the metal in the correct oxidation state. It has been found that, in general, the greater the number of triflate groups bonded to the metal cation, the more active the metal compound will be as a catalyst. It is preferred if half or more of the anions (Z) bound to each metal cation is triflate or a similar anion. The metal catalysts may optionally contain one or more neutral ligands coordinated to the metal . By a neutral ligand is meant a neutral compound that can coordinate with the catalysts, usually the metal cation. Neutral ligands include water, and ethers such as dimethyl ether and tetrahydrofuran. Useful compounds containing neutral ligands include bis (n-cyclopenta- dienyl)tetrahydrofuran-bis (trifluoromethanesulfonato) - zirconium and bis (n-cyclopentadienyl)tetrahydrofuran- bis (trifluoromethanesulfonato)hafnium. The metals catalysts may contain other anions than triflate and similar anions, and tetrafluoroborate, although at least one of triflate or tetrafluoroborate anions must be present. Some other useful anions are alkoxide, particularly lower alkoxide containing 1-4 carbon atoms, acetylacetonate, cyclopentadieneide, pentamethylcyclopentadieneide, t-butylacetylacetonate, and halide . It is preferred if all of the anions are triflate.

It is believed that in the present process, the higher the ratio of metal catalyst compound to monomers.

the lower the molecular weight of the resulting copolymer will be. It is also believed that the copolymer is a random copolymer, except that -0(0)CQC(0)- cannot be adjacent to itself. It is further believed that simple monomers such as THF and, say, succinic or maleic anhydrides, have about an equal propensity to polymerize into the copolymer.

The temperature at which the polymerization process is run is not critical, about -80°C to about 110°C being a convenient range, about 0°C to about 110°C is preferred, and about 25°C to about 65°C is especially preferred. At temperatures above the boiling point of the THF, a pressure vessel may be needed to contain that monomer. It is preferred to run the polymerization neat, that is in the absence of solvent. However, inert solvents such as ethyl ether or toluene may be present if desired. Mild agitation to keep the process ingredients well mixed is preferred. The polymerization is mildly exothermic and agitation also prevents "hot spots" from forming. If the process temperature increases appreciably, refluxing of a volatile monomer (or solvent) may be used to cool the process. The polymerization may take as long as a day, however, more common times are 1 to 2 hours. It is preferred to run the polymerization under dry (water free) conditions to avoid needless decomposition of the ingredients and/or products, and therefor the ingredients should also preferably be dry. It is convenient to use an inert atmosphere such as dry nitrogen. The polymer may be isolated by removing volatiles by evaporation, of if the polymer is insoluble, by filtration. In general, the catalyst may be removed from the copolymer by washing the copolymer with water. In many cases, the catalyst may be reused in the polymerization.

The molar ratio of the THF to cyclic carboxylic anhydride can be about 0.2 to about 60, preferably about 2 to about 15, and most preferably about 5.

The polymerization process may be carried out in a number of ways known to the artisan. It can be done by batch, semibatch and continuous processes. Continuous processes include continuous stirred tank reactor(s) and/or plug flow reactors.

The polymer produced by the instant process contains the repeat units -OCHR ¹ CR ² R ³ CR ² R ³ CHR ⁴ - and -0(0)CQC(0) -, wherein the repeat units are randomly incorporated, except that -0(0)CQC(0)- cannot be adjacent to itself. The definitions of R ¹ , R ² , R ³ , R ⁴ and Q are as given above. The copolymers may be hydrogenated to a polytetrahydrofuran if succinic anhydride is used, or a mixed polyether if another anhydride is used. The copolymers, particularly those containing relatively small amounts of repeat units derived from cyclic carboxylic anhydrides, may also be completely hydrolyzed to polytetrahydrofuran. Such polyethers are useful (usually in their diol form) as monomers for condensation polymers such as polyesters or polyurethanes.

Synthesis of the catalysts used herein are demonstrated by Experiments 1-3 below.

EXPERIMENT 1 Preparation of Bis (n-cyclopentadienyl)tetra- hvdrofuran-bis (trifluoromethanesulfonato)hafnium In a dry box, hafnocene dichloride (9.93 g) was dissolved in THF (300 mL) . To this solution, with stirring, was added a solution of silver triflate (14.12 g) in THF (100 mL) . After 10 minutes the precipitated silver chloride was filtered off and the resulting filtrate concentrated to approximately half its volume at reduced pressure. Hexane (250 mL) was

added and the resulting mixture placed in the freezer. The resulting precipitate was filtered and then dried under vacuum. Yield: 10.02 g. ^X H NMR (CDCI3) : 6.68

(s, 10 H) , 3.76 (m, 4H) , 1.84 (m, 4H) . EXPERIMENT 2

Preparation of Bis(pentamethyl-n-cyclopentadienyl)- bis (trifluoromethanesulfonato) zirconium In a dry box, bis (pentamethylcyclopentadienyl) - zirconium dichloride (10.00 g) was dissolved in THF (300 mL) . To this solution, with stirring, was added a solution of silver triflate (12.46 g) in THF (100 mL) . After 15 minutes the precipitated silver chloride was filtered off and the resulting filtrate concentrated to approximately half its volume at reduced pressure. Hexane (250 mL) was added and the resulting mixture placed in the freezer. The resulting yellow precipitate was filtered and then dried under vacuum. Yield: 6.02 g. ¹ H NMR (CDCI3) : 2.12 (s) .

EXPERIMENT 3 Preparation of Bis (.n-cyclopentadienyl)- bis (trifluoromethanesulfonato) anadium In a dry box, vanadocene dichloride (5.00 g) was dissolved in THF (300 mL) . To this solution, with stirring, was added a solution of silver triflate (11.19 g) in THF (100 mL) . After 15 minutes the precipitated silver chloride was filtered off and the resulting filtrate concentrated to approximately half its volume at reduced pressure. Hexane (250 mL) was added and the resulting mixture placed in the freezer. The resulting green precipitate was filtered and then dried under vacuum. Yield: 6.99 g.

In the Examples, the following abbreviations are used:

GPC - gel permeation chromatography Mn - number average molecular weight

Mw - weight average molecular weight PD - polydispersity, Mw/Mn PS - polystyrene RB - round-bottomed THF - the compound tetrahydrofuran

EXAMPLE 1 Yttrium Triflate Catalyzed Copolymerization of Maleic Anhydride and THF In a dry box, yttrium triflate (1.00 g) and maleic anhydride (2.00 g) were weighed in an oven dried 100 mL RB flask equipped with a stirring bar. The flask was sealed with a rubber septum and removed from the dry box and a nitrogen bleed attached. THF (20 mL) was added via syringe. After 2 hrs. the polymerization was terminated via the addition of water (25 mL) and THF

(50 mL) , the organic phase was separated, concentrated at reduced pressure and dried under vacuum. Polymer yield: 3.38 g. GPC analysis: Mn = 96800, Mw = 188000, PD = 1.95 (PS STD.) . ¹ H NMR analysis indicates the THF to anhydride ratio to be -15.

EX.AMPLE 2 Yttrium Triflate Catalyzed Copolymerization of Succinic Anhydride and THF In a dry box, yttrium triflate (1.00 g) and succinic anhydride (2.00 g) were weighed in an oven dried 100 mL RB flask equipped with a stirring bar. After sealing with a rubber septum the flask was removed from the dry box and a nitrogen bleed attached. THF (20 mL) was added via syringe. After 2 hrs. the polymerization was terminated via the addition of water (25 mL) and THF (50 mL) . The resulting organic phase was separated, concentrated at reduced pressure and dried under vacuum. Polymer yield: 5.00 g. GPC analysis: Mn = 80900, Mw = 171000, PD = 2.12 (PS STD.) .

^λ E NMR analysis indicates the THF to anhydride ratio to be -4.5.

EXAMPLE 3 Yttrium Triflate Catalyzed Copolymerization of Maleic Anhydride and THF at 40°C

In a dry box, yttrium triflate (1.00 g) and maleic anhydride (3.00 g) were weighed in an oven dried 100 mL RB flask equipped with a stirring bar. After sealing with a rubber septum, the flask was removed from the dry box and a nitrogen bleed attached, the flask was then placed in an oil bath maintained at 40°C. THF (20 mL) was then added via syringe. After 2 hrs. the polymerization was terminated via the addition of water (25 mL) , THF (50 L) and diethyl ether (25 mL) the resulting organic phase was separated, concentrated at reduced pressure and dried under vacuum. Polymer yield: 6.16 g. GPC analysis: Mn = 34800, Mw = 74100, PD ^* = 2.13 (PS STD.) .

EXAMPLE 4 Yttrium Triflate Catalyzed Copolymerization of Phthalic Anhydride and THF at 40°C In a dry box, yttrium triflate (1.00 g) and phthalic anhydride (3.00 g) were weighed in an oven dried 100 mL RB flask equipped with a stirring bar. The flask was sealed with a rubber septum and removed from the dry box. A nitrogen purge was attached and the flask placed in an oil bath maintained at 40°C. THF (20 mL) was immediately added and the resulting solution stirred at this temperature for 2 hrs. The polymerization was terminated by the addition of water

(25 mL) and THF (50 mL) , the resulting organic phase was separated, concentrated at reduced pressure and then dried under vacuum. Polymer yield: 7.04 g. GPC analysis: Mn = 69400, Mw « ^*•* 128000, PD = 1.85 (PS STD.) .

¹ H NMR analysis indicates the THF to anhydride ratio to be -3.6.

EXAMPLE 5 Y terhinm Triflate Catalyzed Copolymerization of Cis-l-2-Cvclohexane-Dicarboxylic Anhydride and THF at 4Q°C In a dry box, ytterbium triflate (1.00 g) and cis-l,2-cyclohexanedicarboxylic anhydride (1.5 g) were weighed in an oven dried 100 mL RB flask equipped with a stirring bar. The flask was sealed with a rubber septum and removed from the dry box. A nitrogen purge was attached and the flask placed in an oil bath maintained at 40°C. THF (20 mL) was immediately added and the resulting solution stirred at this temperature for 60 min. The polymerization was terminated by the addition of water (25 mL) and THF (50 mL) , the resulting organic phase was separated, concentrated at reduced pressure and then dried under vacuum. Polymer yield: 9.26 g. GPC analysis: Mn = 38100, Mw = 83500, PD = 2.15 (PS STD.) .

Yttrium Triflate Catalyzed Copolymerization of NorbQrnene-2,3-dicarfc>pχylic .Anhydride and THF at 40°C In a dry box, yttrium triflate (1.00 g) and norbornene-2,3-dicarboxylic anhydride (4.0 g, 96%) were weighed in an oven dried 100 mL RB flask equipped with a stirring bar. The flask was sealed with a rubber septum and removed from the dry box. After the attachment of a nitrogen purge THF (20 mL) was added and the resulting solution stirred at room temperature for 60 min. The polymerization was terminated by the addition of water (25 mL) and THF (50 mL) , the resulting organic phase was separated, concentrated at reduced pressure and then

dried under vacuum. Polymer yield: 5.13 g. GPC analysis: Mn = 52400, Mw = 111000, PD = 2.13 (PS STD.) .

EXAMPLE 7 Erbium Triflate Catalyzed Copolymerization of Cis-1.2-Cyclohexane-Dicarboxylic Anhydride and THF

In a dry box, erbium triflate (1.00 g) and cis-1,2- cyclohexane-dicarboxylic anhydride (1.5 g) were weighed in an oven dried 100 mL RB flask equipped with a stirring bar. The flask was sealed with a rubber septum and removed from the dry box. A nitrogen purge was attched, THF (20 mL) was immediately added and the resulting solution stirred at room temperature for 120 min. The polymerization was terminated by the addition of water (25 mL) and THF (50 mL) , the resulting organic phase was separated, concentrated at reduced pressure and then dried under vacuum. Polymer yield: 3.03 g.

EXAMPLE 8 Neod mium Triflate Catalyzed Copolymerization of Cis-1.2-Cyclohexanedicarboxylic Anhydride and THF In a dry box, neodymium triflate (1.00 g) and cis-l,2-cyclohexanedicarboxylic anhydride (1.5 g) were weighed in an oven dried 100 mL RB flask equipped with a stirring bar. The flask was sealed with a rubber septum and removed from the dry box. A nitrogen purge was attched, THF (20 mL) was immediately added and the resulting solution stirred at room temperature for 120 min. The polymerization was terminated by the addition of water (25 mL) and THF (50 mL) , the resulting organic phase was separated, concentrated at reduced pressure and then dried under vacuum. Polymer yield: 1.39 g.

EXAMPLE 9 Dysprosium Triflate Catalyzed Copolymerization of

Cis-lr -CyclohexanedicarbQxylic Anhydride and THF In a dry box, dysprosium triflate (1.00 g) and cis-l,2-cyclohexanedicarboxylic anhydride (1.5 g) were weighed in an oven dried 100 mL RB flask equipped with a stirring bar. The flask was sealed with a rubber septum and removed from the dry box. A nitrogen purge was attched, THF (20 mL) was immediately added and the resulting solution stirred at room temperature for 120 min. The polymerization was terminated by the addition of water (25 mL) and THF (50 mL) , the resulting organic phase was separated, concentrated at reduced pressure and then dried under vacuum. Polymer yield: 1.96 g.

EXAMPLE 10

Scandium Triflate Catalyzed Copolymerization of

Cis-1.2-Cyclohexanedicarboxylic Anhydride and THF In a dry box, scandium triflate (1.00 g) and cis-l,2-cyclohexanedicarboxylic anhydride (1.5 g) were weighed in an oven dried 100 mL RB flask equipped with a stirring bar. The flask was sealed with a rubber septum and removed from the dry box. A nitrogen purge was attched, THF (20 mL) was immediately added and the resulting solution stirred at room temperature for 120 min. The polymerization was terminated by the addition of water (25 mL) and THF (50 mL) , the resulting organic phase was separated, concentrated at reduced pressure and then dried under vacuum. Polymer yield: 1.30 g.

EXAMPLE 11 Ytterbium Triflate Catalyzed Copolymerization of Succinic Anhydride. THF and 3-Methyl-THF In a dry box, ytterbium triflate (2.00 g) and succinic anhydride (2.00 g) were weighed in an oven

dried 100 mL RB flask equipped with a stirring bar. After sealing with a rubber septum the flask was removed from the dry box and a nitrogen bleed attached. THF (15.00 mL) and 3-methyl-THF (5.00 mL) were added via syringe. After 2 hrs the polymerization was terminated via the addition of water (25 mL) and THF (50 mL) and ether (25 mL) . The resulting organic phase was separated, concentrated at reduced pressure and dried under vacuum. Polymer yield: 4.32 g. GPC analysis (PS STD.) : Mn = 26100, Mw = 43100, PD = 1.65.

EXAMPLE 12 Ytterbium Triflate Catalyzed Copolymerization of Succinic Anhydride. THF and 3-Methvl-THF In a dry box, ytterbium triflate (2.00 g) and succinic anhydride (3.00 g) were weighed in an oven dried 100 mL RB flask equipped with a stirring bar. After sealing with a rubber septum the flask was removed from the dry box and a nitrogen bleed attached. THF (15.00 mL) and 3-methyl-THF (5.00 mL) were added via syringe. After 2 hrs the polymerization was terminated via the addition of water (25 L) and THF (50 mL) and ether (25 mL) . The resulting organic phase was separated, concentrated at reduced pressure and dried under vacuum. Polymer yield: 7.27 g. GPC Analysis (PS STD.) : Mn = 30600, Mw = 52400, PD = 1.71.

EXAMPLE 13 Zirconium Triflate Catalyzed Copolymerization of 1.2.4.5-Benzenetetracarboxylic Dianhydride and THF In a dry box, zirconium triflate (2.00 g) and 1,2, 4, 5-benzenetetracarboxylic dianhydride (4.00 g) were weighed in an oven dried 100 mL RB flask equipped with a stirring bar. After sealing with a rubber septum the flask was removed from the dry box and a nitrogen bleed attached. THF (20.00 mL) was added via syringe. After 2 hrs the polymerization was terminated via the addition

of water (25 mL) . The resulting slurry was concentrated at reduced pressure, resulting in a thick viscous material. This material was washed repeatedly with water and then dried under vacuum. Polymer yield: 7.12 g.

EXAMPLE 14 Bis (n-cyclopentad-ienyl)te rahydrofuran- bis (trifluoromethanesulfonato'i zirconium Catalyzed Copolymerization of Maleic Anhydride and THF In a dry box, bis (n-cyclopentadienyl)tetrahydro- furan-bis (trifluoromethanesulfonato) zirconium (0.50 g) and maleic anhydride (1.00 g) were added an oven dried 100 mL RB flask equipped with a stirring bar. The flask was sealed with a rubber septum and removed from the dry box. After the attachment of a nitrogen bleed THF (10 mL) was added to the flask. After 75 min. the polymerization was terminated via the addition of water (25 mL) , THF (50 mL) and ether (25 mL) . The resulting organic phase was separated, concentrated at reduced pressure and then dried under vacuum. Polymer yield: 0.73 g. GPC analysis (PS STD.) : Mn = 56500, Mw = 71600, PD = 1.27.

EXAMPLE 15 Tin Triflate Catalyzed Copolymerization of Cis--l,2-CyclohexaneDicarbPxylic Anhydride and THF In a dry box, tin triflate (1.00 g) and cis-1,2- cyclohexanedicarboxylic anhydride (1.5 g) were weighed in an oven dried 100 mL RB flask equipped with a stirring bar. The flask was sealed with a rubber septum and removed from the dry box. A nitrogen purge was attched, THF (20 mL) was immediately added and the resulting solution stirred at room temperature for 120 min. The polymerization was terminated by the addition of water (25 mL) and THF (50 mL) , the resulting organic phase was separated, concentrated at reduced

pressure and then dried under vacuum. Polymer yield: 1.41 g.