Glycolic acid polymers and method of producing the same

Abstract

Described herein is a feasible, significantly simplified production method that avoids challenging lactonization steps and converts a low molecular weight aliphatic polyester, consisting of hydroxy acids and a comonomer, whose molecular weight has been increased by step-growth polymerization reactions. The molecular weight of the aliphatic polyester, based on comparison of initial and final weight average molecular weights (M w,1/ M w,2 ), increased significantly at a rate which permits the use of reactive extrusion to produce high molecular weight aliphatic polyesters in a simple, economically feasible manner.

What is claimed is: 
     
         1 . A telechelic polymers of glycolic acid obtained by a process comprising the steps of
 providing glycolic acid;   providing a difunctional monomer;   subjecting said glycolic acid to condensation polymerization in the presence of said monomer; and   continuing polymerization to provide a polymeric chain formed by residues derived from glycolic acid and said difunctional monomer.   
     
     
         2 . The polymers according to  claim 1 , comprising at least 5, for example 5 to 250, preferably 6 to 100, in particular 10 to 50 residues of glycolic acid. 
     
     
         3 . The polymers according to  claim 1 , comprising an essentially linear polymeric chain or a branched polymeric chain. 
     
     
         4 . The polymers according to  claim 1 , having a degree of crystallinity of at least 30%, preferably at least 40%, in particular at least 50%. 
     
     
         5 . The polymer according to  claim 1 , comprising at least 80 mol-%, preferably at least 90 mol-%, of residues derived from glycolic acid. 
     
     
         6 . The polymer according to  claim 1 , comprising 0.5 to 10 mol-%, preferably 1 to 5 mol-%, of residues derived from a difunctional comonomer, e.g. a hydroxy-terminated comonomer. 
     
     
         7 . The polymer according to  claim 5 , wherein the molar ratio between residues derived from glycolic acid and residues derived from the comonomer is 1000:1 or less, for example 500:1 or less, suitably 300:1 or less, advantageously 45:1 to 55:1, in particular 48:1 to 52:1. 
     
     
         8 . The polymer according to  claim 6 , wherein the hydroxy-terminated comomer is selected from the group of diols, such as propanediol, butanediol, hexanediol, pentaerythriol and oligomeric polyethylene glycol and combinations thereof. 
     
     
         9 . The polymer according to  claim 1 , which is a telechelic hydroxy-terminated polymer, preferably exhibiting exclusively comonomer residues of hydroxy-terminated comonomers. 
     
     
         10 . The polymer according to  claim 7 , wherein the comonomer is selected from a dicarboxylic acid, dithiol, or diamine. 
     
     
         11 . The polymer according to  claim 1 , wherein the glycolic acid is subjected to condensation polymerization in the presence of the monomer a and a catalyst, preferably an esterification catalyst. 
     
     
         12 . The polymer according to  claim 1 , comprising 0 to 20, preferably 0 to 10 mol-% of residues of at least a second hydroxy acid, e.g. lactic acid. 
     
     
         13 . The polymer according to  claim 1 , having a molecular weight (Mn) of 500 to 25,000, in particular about 750 to 15,000 g/mol. 
     
     
         14 . The polymer according to  claim 1 , capable of being used as a prepolymer for producing polymers. 
     
     
         15 . A method of producing a telechelic polymer of glycolic acid, comprising the steps of
 providing glycolic acid;   providing a difunctional monomer;   subjecting said glycolic acid to polymerization in the presence of a catalyst and said difunctional monomer; and   continuing polymerization to provide a polymeric chain formed by residues derived from glycolic acid and said monomer.   
     
     
         16 . The method according to  claim 15 , wherein a hydroxyl-terminated polymer chain is formed by the steps of
 providing glycolic acid;   providing a hydroxy-terminated monomer;   subjecting said glycolic acid to condensation polymerization in the presence of an esterification catalyst and said hydroxy-terminated monomer;   continuously removing water formed during condensation polymerization; and   continuing polymerization to provide a polymeric chain formed by residues derived from glycolic acid and said hydroxy-terminated monomer.   
     
     
         17 . A method of producing a telechelic polyester polymer of glycolic acid, which preferably is hydroxy-terminated, optionally in combination with a method according to  claim 15 , wherein polymerization of the corresponding monomers is carried out in an initial solid state at 200° C. or less for a pro-longed period of time under reduced pressure, followed by a final dehydration, the initial polymerization being carried out for a time of less than 36 h and dehydration step being carried out at a time of less than 24 h. 
     
     
         18 . The method according to  claim 15 , wherein condensation polymerization, optionally in combination with a dehydration step, is continued until a polymer comprising least 5, for example 5 to 250, advantageously 6 to 100, in particular 10 to 50 residues of glycolic acid is obtained. 
     
     
         19 . A method according to  claim 1  for preparing glycolic acid homo- or copolymers. 
     
     
         20 . The method according to  claims 15 , wherein condensation polymerization is carried out at a temperature of 120 to 250° C., optionally in an inert atmosphere or under reduced pressure. 
     
     
         21 . The method according to  claim 15 , wherein condensation polymerisation of glycolic acid is performed at temperatures below the melting point of the product polyglycolic acid, in particular condensation polymerisation of glycolic acid is performed at temperatures below 210° C. 
     
     
         22 . The method according to  claim 15 , wherein the temperature of the polymerisation of glycolic acid is gradually increased and the absolute pressure decreased. 
     
     
         23 . The method according to  claim 15 , wherein condensation polymerization is carried out in the presence of a catalyst selected from the group of zinc, tin or titanium octoate. 
     
     
         24 . The method according to  claim 15 , wherein condensation polymerization is carried out in the presence of a comonomer, e.g. a second hydroxy acid, such as lactic acid. 
     
     
         25 . The method according to  claim 15 , wherein polymerization is continued to provide an essentially linear hydroxy-terminated polymeric chain. 
     
     
         26 . The method according to  claim 15 , wherein polymerization is continued to provide an essentially branched hydroxy-terminated polymeric chain. 
     
     
         27 . The method according to  claim 15 , wherein polymerization is carried out in a solvent. 
     
     
         28 . A glycolic acid polymer comprising at least two prepolymers, preferably 5 to 100 prepolymers, according to  claim 1  linked together. 
     
     
         29 . A polymer according to  claim 28 , comprising prepolymers linked together with chain extenders, e.g. chain extenders selected from the group of diepoxides or diisocyanates. 
     
     
         30 . A polymer according to  claim 28 , retaining at least 30%, preferably at least 40% of the crystallinity or melting enthalpy of the prepolymer. 
     
     
         31 . A polymer according to  claim 28 , having a molecular weight (Mn) of more than 10,000 g/mol, in particular about 20,000 to 1,000,000 g/mol. 
     
     
         32 . A polymer according to  claim 28 , having an essentially linear polymer structure or an essentially branched polymer structure. 
     
     
         33 . A method of producing a polymer according to  claim 28 , comprising subjecting a prepolymer to step-growth polymerization in the presence of a chain extender to provide a linear polymer having a molecular weight (Mn) of more than 10,000 g/mol, in particular about 20,000 to 1,000,000 g/mol. 
     
     
         34 . The method according to  claim 33 , wherein the chain extenders are selected from the group of diepoxides and diisocyanates. 
     
     
         35 . The method according to  claim 33 , carried out in an extruder, e.g. in a twin screw extruder for achieving step growth polymerization. 
     
     
         36 . Use of polymers according to  claim 28  for forming polymeric films, sheets, fibers, powders or moulded articles, in particular for forming compression-moulded, injection-moulded, blow-moulded products, and other formed or moulded products. 
     
     
         37 . The use according to  claim 36 , wherein the polymers are used for forming products exhibiting properties of good heat and chemical resistance as well as good gas barrier properties, e.g. excellent oxygen and carbon dioxide barrier properties. 
     
     
         38 . The use according to  claim 36  for coating of specimens, preferably selected from the group of solid objects and webs, in particular by thermal powder coating or extrusion coating. 
     
     
         39 . The use according to  claim 36 , wherein the polymer is used directly from reactive processing for extrusion or moulding.