Ring-opening polymerization of cyclic esters, polyesters formed thereby, and articles comprising the polyesters

Abstract

Cyclic esters are polymerized in the presence of a catalytic amount of a Group 4 transition metal hydride. The method is capable of producing high molecular weight polyesters with low polydispersities. These high molecular weight polyesters exhibit improved mechanical properties and are useful in a variety of product applications.

1 . A method of preparing a polyester comprising:
 polymerizing a cyclic ester in the presence of a catalytic amount of a catalyst consisting of a Group 4 transition metal hydride having the structure Cp′ 2 M(H)(R), wherein Cp′ is an unsubstituted or substituted cyclopentadienyl ligand; M is titanium, zirconium, or hafnium; and R is hydrogen, halogen, C 1 -C 12 , hydrocarbyl, or C 1 -C 12  hydrocarbyloxy; wherein the Group 4 transition metal hydride is generated in situ by reaction of a Group 4 transition metal complex with a metal hydride reagent comprising a metal other than a Group 4 transition metal, and wherein the Group 4 transition metal complex has the structure Cp′ 2 MX 2 , wherein Cp′ and M are as previously defined, and each occurrence of X is independently chloride, bromide, iodide, C 1 -C 12  hydrocarbyl, or C 1 -C 12  hydrocarbyloxy.   
   
   
       2 . The method of  claim 1 , wherein the metal hydride reagent is selected from the group consisting of aluminum hydride reagents and borohydride reagents. 
   
   
       3 . The method of  claim 1 , wherein the metal hydride reagent is selected from the group consisting of diisobutylaluminum hydride (DIBAH), sodium bis(2-methoxyethoxy)aluminum dihydride (Vitride), lithium tri-tert-butoxyaluminum hydride, and mixtures thereof. 
   
   
       4 . A method of preparing a polyester, comprising: reacting a Group 4 transition metal halide with a silver (I) salt to form a silver halide and a cationic Group 4 transition metal complex; wherein the Group 4 transition metal halide has structure Cp′ 2 MX 2 , wherein Cp′ is an unsubstituted or substituted cyclopentadienyl ligand; M is titanium, zirconium, or hafnium; and X is chloride, bromide, or iodide; and
 polymerizing a cyclic ester in the presence of a catalytic amount of the cationic Group 4 transition metal complex.   
   
   
       5 . A method of preparing a polyester comprising:
 reacting a Group 4 transition metal hydride with an oxygen-containing compound selected from the group consisting of aldehydes, ketones, epoxides, peroxides, anhydrides, carboxylic acids, esters, amides, and vinyl ethers to form a Group 4 transition metal alkoxide intermediate; wherein the Group 4 transition metal hydride has structure Cp′ 2 M(H)(R), wherein Cp′ is an unsubstituted or substituted cyclopentadienyl ligand; M is titanium, zirconium, or hafnium; and R is hydrogen, halogen, C 1 -C 12 , hydrocarbyl, or C 1 -C 12  hydrocarbyloxy; and   polymerizing a cyclic ester in the presence of a catalytic amount of a catalyst consisting of the Group 4 transition metal alkoxide intermediate.   
   
   
       6 . A polycaprolactone having a number average molecular weight of about 100,000 to about 1,000,000 atomic mass units. 
   
   
       7 . An article comprising the polycaprolactone of  claim 6 . 
   
   
       8 . A polycaprolactone having a number average molecular weight of about 100,000 to about 600,000 atomic mass units. 
   
   
       9 . An article comprising the polycaprolactone of  claim 8 . 
   
   
       10 . A polycaprolactone exhibiting at least one of
 a storage modulus, G′, of at least 10 kilopascals at 90° C. and a shear rate of 0.001 to 1,000 rad/sec,   a loss modulus, G″, of at least 10 kilopascals at 90° C. and a shear rate of 0.001 to 1,000 rad/sec,   a complex modulus, G*, of at least 10 kilopascals at 90° C. and a shear rate of 0.001 to 1,000 rad/sec,   a complex shear viscosity, η, of 10 kilopascals to 10 megapascals at 90° C. and a shear rate of 0.001 to 1,000 rad/sec,   a tensile elongation at break of at least 2,000% measured at 23° C.,   a tensile strength at yield of at least 15 megapascals measured at 23° C.,   a modulus of elasticity of at least 100 megapascals measured at 23° C.,   a Young's modulus of at least 30 megapascals measured at 23° C., and   an ultimate tensile strength of at least 20 megapascals measured at 23° C.   
   
   
       11 . An article comprising the polycaprolactone of  claim 10 . 
   
   
       12 . A polyester comprising a terminal residue having the structure -OMCp′ 2 X, wherein M is titanium, zirconium, or hafnium; each occurrence of Cp′ is independently an unsubstituted or substituted cyclopentadienyl ligand; and X is chloride, bromide, iodide, C 1 -C 12  hydrocarbyl, or C 1 -C 12  hydrocarbyloxy. 
   
   
       13 . A polycaprolactone comprising a terminal residue having the structure -OZrCp′ 2 Cl, wherein each occurrence of Cp′ is independently an unsubstituted or substituted cyclopentadienyl ligand. 
   
   
       14 . A method of depolymerizing a polymer comprising ester linkages, comprising:
 mixing the polymer comprising ester linkages with a catalytic amount of a Group 4 transition metal hydride to form a mixture; and   maintaining the mixture at a temperature and for a time effective to depolymerize the polymer comprising ester linkages.   
   
   
       15 . A method of depolymerizing a polycaprolactone, comprising:
 mixing a polycaprolactone and a catalytic amount of bis(cyclopentadienyl)zirconium(chloride)(hydride) to form a mixture; and   maintaining the mixture at a temperature of about 0 to about 200° C. for about 1 to about 200 hours.   
   
   
       16 . The method of  claim 15 , wherein the mixture further comprises a solvent.