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 (Mw,1 / Mw,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.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application is a Continuation-In-Part Application of International Patent Application No. PCT / FI2014 / 050334 filed May 6, 2014, which claims priority to Finnish Patent Application No. 20135467 filed on May 6, 2013, each of which is hereby incorporated by reference in its entirety.TECHNICAL FIELD[0002]The present invention relates to polyesters. In particular, the present invention concerns the synthesis difunctional aliphatic polyesters, which may exhibit a low molecular weight limiting their use in practise, conversion of such polymers to a higher molecular weight polymeric material and production methods thereof leading to products derived mainly from hydroxy acids, particularly but not exclusively, from glycolic acid.BACKGROUND ART[0003]Polyglycolic acid, prepared from the smallest member of the α-hydroxy acid family, has been produced and copolymerized by condensation polymerization processes for decades. (cf. U.S. Pat. No. 2,676,...

AI Technical Summary

Benefits of technology

[0010]It is a third objective of this invention to provide methods to prepare a suitable α,ω-difunctional polyglycolic acid polymer prepared by but not limited to a condensation process which can be efficiently utilized in step-growth polymerizations to increase its molecular weight.

[0016]The present invention is based on the formation of a polyglycolic acid polymer, or optionally copolymer, which can undergo step-growth reactions to increase its molecular weight. By a subsequent step-growth polymerization step of a polyglycolic acid polymer, or optionally copolymer, high molecular weights can be achieved which are difficult to achieve for polyglycolic acid, particularly by condensation processes as known for those familiar to the art. In particular, significant benefits are achieved when said polyglycolic acid polymer has been prepared by a condensation process thus avoiding the cumbersome synthesis of glycolide and its subsequent ring-opening polymerization.

Problems solved by technology

A common disadvantage of conventional condensation polymerization is that a polymer exhibiting a low molar mass is typically formed in the process.

Equivalent reactions can be used for lactic acid, albeit with a frequent disadvantage where the desired optical purity of the precursor is lost due to racemization during the polycondensation reactions.

However, the preparation of pure glycolide which yields high molecular weight polyglycolic acid is difficult to achieve.

Processes to prepare lactide, a closely related molecule, result in poor collected yields of glycolide and high amounts of undesired side products which make the glycolide forming process a bottleneck for wider use of the material.

Thus, preparation of glycolide in high yields requires the use of solvents and additives which must be separated from the product and present a technical obstacle for wider use of the materials.

Such methods have been used for lactic acid based materials (U.S. Pat. No. 5,380,813) with a clear disadvantage as the optically pure precursor undergoes racemization during the condensation process losing its crystallinity, thus severely limiting its applicability due to a low glass transition temperature as the sole thermal transition for the material.

As a result, corresponding polymers (PLAs) are not crystalline and their use is limited.

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