Multiblock copolymers containing poly(butylene succinate) and poly(ε-caprolactone) blocks: Effect of block ratio and length on physical properties and biodegradability

Abstract

In order to obtain polymers with preserved thermal properties and tunable biodegradability multiblock copolymers comprising blocks of biodegradable polyesters poly(ε-caprolactone) (PCL) and poly(butylene succinate) (PBS) were successfully synthesized through chain-extension reaction using hexamethylene diisocyanate. Two series of copolymers with different length of PCL block and varying ratio of PCL and PBS block through each series were synthesized. PCL-b-PBS copolymers were characterized by NMR, FTIR, WAXS, DSC, TG and DMA in solid state. Special attention was given to the investigation of the influence of composition and structure of multiblock copolymers on their biodegradability properties. Biodegradability of these multiblock copolymers was assessed through hydrolysis in alkaline medium and soil burial test. Each block in multiblock copolymers crystallized separately, with adverse influence of its presence on degree of crystallinity and, in much lesser extent, on melting temperature of the second phase. Multiblock copolymers showed high thermal stability, comparable to corresponding homopolymers. Mechanical strength, deduced from storage modulus in glassy and rubbery state, was a firm function of composition. Copolymers rich in PBS were more prone to degradation through simple hydrolysis in alkaline medium, while PCL-rich copolymers were more susceptible to degradation by soil microorganisms. Through the change in copolymer composition, degradability in different environments could be tailored without compromising materials’ thermal properties. Besides composition, molecular weight of copolymers had the major influence on degradability properties.