Thermal properties and biodegradability of the copolymers of l-lactide, ɛ-caprolactone, and ethylene glycol oligomer with maleate units and their crosslinked products

Copolymers of l-lactide (LLA), ɛ-caprolactone (CL), and ethylene glycol oligomer (EGO) were synthesized by ring-opening copolymerization of CL and LLA initiated by EGO at the LLA/CL molar ratios of 7/3, 5/5, and 3/7. The resulting viscous ternary copolymers (PLCE) with weight average molecular weight (Mw) ca. 3000 were reacted with maleic anhydride to give unsaturated group-containing copolymer (PLCEM) with Mw 6000–8000. The degree of unsaturation of PLCEM was 0.3–0.6 per one EGO block. The PLCEM was cured with benzoyl peroxide (BPO) to give a viscoelastic soft material insoluble in any solvent. The DSC analysis of the copolymers revealed that all the copolymers are amorphous materials having a glass transition temperature (Tg), which increased with increasing LLA/CL ratio. The crosslinked PLCEM showed a higher Tg than the corresponding PLCE and PLCEM. The crosslinked PLCEM showed good biodegradability, when measured by a BOD method using activated sludge.