Study on the hydrolytic degradation of glycolide/trimethylene carbonate copolymers having different microstructure and composition

Abstract

Hydrolytic degradation of a series of copolymers synthesized by ring opening polymerization of trimethylene carbonate and glycolide was studied by following the weight loss and changes in molecular weight, polydispersity index and mechanical properties. Analyses of 1H NMR and FTIR spectra taken during exposure to a pH 7.4 phosphate buffered solution were also performed. Copolymers with different microstructures (i.e. random, triblock and segmented copolymers) were synthesized. Most segmented copolymers studied had identical trimethylene carbonate content but differed in the hard segment content. Composition was also varied to demonstrate the influence of the soft segment composition.Results were consistent with a model where degradation started in the amorphous phases and affected the glycolide units of the less compact soft segments and the regions within lamellar stacks. This degradation step led to a clear decrease of GGG triads (NMR data) and amorphous glycolide content (FTIR data), as well as an increase in Young's modulus. Degradation subsequently proceeded through the crystalline glycolide units belonging to lamellar stacks. The molecular weight of the degraded samples reached always an asymptotic value that corresponded to a solubility limit for fragments with high TMC content and for highly crystalline entities constituted by glycolide rich fragments.Results pointed to the importance of the hard segment content and the composition of the soft segment, which logically influenced the distribution between amorphous and crystalline phases.