In vitro degradation of trimethylene carbonate based (Co)polymers

Trimethylene carbonate (TMC) was copolymerized with D,L-lactide (DLLA) or with epsilon-caprolactone (CL), and the degradation of melt-pressed solid copolymer films in phosphate-buffered saline at pH 7.4 and 37degreesC was followed for a period of over two years. The parent homopolymers were used as reference materials. The degradation profile of TMC-DLLA- and TMC-CL based copolymers was similar and was best described by autocatalyzed bulk hydrolysis, preferentially of ester bonds. The hydrolysis rates varied by two orders of magnitude, depending on polymer composition and physical characteristics under the degradation conditions. TMC-DLLA copolymers degraded faster than the parent homopolymers. The copolymers lost their tensile strength in less than fiver months, after which mass loss occurred. Copolymers with 50 or 80 mol-% of TMC underwent total degradation in eleven months. For TMC-CL copolymer, a slow and gradual decrease in molecular weight and deterioration of the mechanical performance was observed. These copolymers maintained suitable mechanical properties for seventeen months or longer. Chain scission in the semicrystalline copolymers resulted in an increase in crystallinity. In comparison with the CL homopolymer, the introduction of a small amount of TMC (10 mol-%) significantly reduced the increase in crystallinity during degradation. Poly(TMC) specimens were dimensionally stable and showed a negligible decrease in molecular weight. A 60% decrease in the initial tensile strength of the polymer-samples was observed after two years.