Effect of poly(l-lactide) chain length on microstructural and thermo-mechanical properties of poly(l-lactide)-b-poly(butylene carbonate)-b-poly(l-lactide) triblock copolymers

Abstract

A series of ABA type triblock copolymers based on biodegradable poly(butylene carbonate) (PBC) and poly(l-lactide) (PLLA) were synthesized with PBC as the core and varying the PLLA chain length. A significant reduction in the crystallinity of the PBC component is observed in the block copolymers as evidenced by DSC and wide angle X-ray diffraction. A systematic increase in the crystallinity of the PLLA blocks is also observed with increasing chain length of PLLA. The block copolymers undergo a transition from micro-phase separated lamellar morphology to macro-phase separated unstable morphology in the composition domain of ∼45–55 wt% of PLLA. A pseudo-ductile to quasi-brittle transition was observed in the composition range of ∼45–55 wt% of PLLA corresponding to a change in morphology as confirmed by Atomic Force Microscopy and Small Angle X-ray Scattering. This study demonstrates a green path for PLLA toughening by using another biodegradable aliphatic polymer.