Toughening polylactide with nonlinear, degradable analogues of PEG and its copolymers

Abstract

Polylactic acid (PLA) as a bio-sourced polymer has excellent tensile strength but its applications are severely limited due to its inherent brittleness. PLA can be effectively toughened with linear poly(ethylene glycol) (PEG) at the expense of elastic modulus and tensile strength. In this study, a well-defined polyester-based nonlinear PEG analogue, poly(VL-Teg), and its block copolymers, poly(VL-Teg)-b-PLA, have been facilely prepared via controlled ring-opening polymerization with a binary organocatalyst system in bulk. The homo- and co-polymers of the nonlinear PEG analogue are evaluated as toughening additives for PLA. Results reveal that non-linear analogues are effective additives for PLA toughening with a great increase of elongation at break and without a drastic loss of elastic modulus or yield strength. Compared with their linear PEG counterpart, the nonlinear PEG analogues as toughening additives are able to deliver PLA blends with more balanced mechanical properties under similar conditions. In particular, PLA melt-blended with P(VL-Teg)₄₀-b-PLA₄₀ (10 wt% loading) shows over 7-fold improvement in elongation at break and 9-fold higher tensile toughness than a commercial pristine PLA without a significant loss of yield strength (less than 3% reduction).