Absorbable copolymers with improved thermal stability

Abstract

The present invention relates to absorbable block copolymers with improved characteristics including thermal stability, molecular weight consistency, inherent viscosity retention following melt extrusion, and fibers made from the polymers exhibit increased strength.

What is claimed is: 
     
         1 . An absorbable aliphatic polyester copolymer comprising:
 a polyaxial core, with at least three axes, including a pre-polymer;   wherein the at least three axes comprise polymeric chains;   at least one flexible linking segment; and   at least one polymeric end graft comprising repeat units derived from at least one cyclic monomer capable of crystallization, the at least one polymeric end graft attached to each of the at least three axes.   
     
     
         2 . The absorbable aliphatic polyester copolymer of  claim 1 , wherein the polyaxial core comprises crystallizable polymeric chain segments. 
     
     
         3 . The absorbable aliphatic polyester copolymer of  claim 1 , wherein the polyaxial core comprises amorphous chain segments. 
     
     
         4 . The absorbable aliphatic polyester copolymer of  claim 1 , wherein the flexible linking segment and the crystallizable cyclic monomer share a common monomer. 
     
     
         5 . The absorbable aliphatic polyester copolymer of  claim 1 , wherein the flexible linking segments are comprised of the same prepolymer as the polyaxial core and the same crystallizable cyclic monomer as the at least one polymeric end grafts. 
     
     
         6 . The absorbable aliphatic polyester copolymer of  claim 1 , wherein the prepolymer may be a homopolymer, copolymer or terpolymer formed from the group consisting of L,L-lactide and D,L-lactide, glycolide, substituted glycolides, para-dioxanone, 1,5-dioxepan-2-one, trimethylene carbonate, epsilon-caprolactone, alpha-Angelica lactone, gamma-valerolactone and delta-valerolactone, or combinations thereof. 
     
     
         7 . The absorbable aliphatic polyester copolymer of  claim 6 , wherein the pre-polymer is derived from epsilon-caprolactone, trimethylene carbonate, or a combination of the two. 
     
     
         8 . The absorbable aliphatic polyester copolymer of  claim 1 , wherein the pre-polymer is derived from glycolide, trimethylene carbonate or a combination of the two. 
     
     
         9 . The absorbable aliphatic polyester copolymer of  claim 1 , wherein the copolymer comprises at least four distinct blocks including a central crystalizable core with at least three axes including crystalizable end blocks grafted to the at least three axes. 
     
     
         10 . The absorbable aliphatic polyester copolymer of  claim 1 , wherein the at least one crystallizable cyclic monomer is selected from the group consisting of L,L-lactide and D,L-lactide, glycolide, substituted glycolides, para-dioxanone, 1,5-dioxepan-2-one, trimethylene carbonate, epsilon-caprolactone, alpha-Angelica lactone, gamma-valerolactone and delta-valerolactone, or combinations thereof. 
     
     
         11 . The absorbable aliphatic polyester copolymer of  claim 1 , wherein the flexible linking segments may be derived from trimethylene carbonate, ε-caprolactone, or a combination of the two. 
     
     
         12 . The absorbable aliphatic polyester copolymer of  claim 1 , further comprising an absorbable barrier, web, mesh or fabric. 
     
     
         13 . The absorbable aliphatic polyester copolymer of  claim 12 , wherein the copolymer is formed into a warp-knitted mesh. 
     
     
         14 . The absorbable aliphatic polyester copolymer of  claim 1 , further comprising an absorbable polymeric surface coating for controlled drug delivery. 
     
     
         15 . A method for producing an absorbable aliphatic polyester copolymer comprising:
 charging a reactor with a monomer, an initiator, and a catalyst, wherein the monomer to catalyst ratio is at least 25,000;   the initiator having at least one hydroxyl group capable of initiating ring-opening polymerization;   the monomer including at least one cyclic monomer;   heating the reactor to at least 100° C.;   stirring the monomer, initiator, and catalyst to form a homogenous mixture prepolymer, wherein weight of the prepolymer is greater than 10 kDa; and   forming a copolymer with multiple amorphous prepolymer axes and crystalline end grafts emanating from each axis.   
     
     
         16 . The method of  claim 15  wherein the catalyst is stannous octoate. 
     
     
         17 . The method of  claim 15 , wherein the initiator is selected from the group consisting hydroxyl bearing small molecules, oligomers, polymers, and also inorganic and organic salts, or combinations of the above. 
     
     
         18 . The method of  claim 17 , wherein the initiator is selected from the group consisting of 1-decanol, 1,3-propanediol, trimethylolpropane, triethanolamine, 1,3,4-trihydroxy-2-butanone, glycerol or combinations of the above. 
     
     
         19 . The method of  claim 15 , wherein the monomer is a copolymer or terpolymer derived from lactide, trimethylene carbonate, and/or ε-caprolactone. 
     
     
         20 . The method of  claim 15 , wherein the monomer is a copolymer or terpolymer derived from glycolide, trimethylene carbonate, and/or ε-caprolactone. 
     
     
         21 . The method of  claim 15 , wherein the monomer is a substituted glycolide. 
     
     
         22 . The method of  claim 15 , where a second charge of catalyst is added to the reactor. 
     
     
         23 . The method of  claim 15 , where two independent temperature settings are established during the reaction.