Syntheses and properties of tri- and multi-block copolymers consisting of polybutadiene and polylactide segments

Biomaterials have drawn considerable attention in recent years because of environmental concerns. In this paper, several different poly(lactide)-b-poly(butadiene)-b-poly(lactide) (PLA-b-PB-b-PLA) triblock copolymers were synthesized by the bulk ring-opening polymerization of lactide initiated by flexible macro-initiator hydroxyl-terminated polybutadiene (HTPB) by adjusting the ratio of HTPB to lactide and the optical isomer of lactide. Afterwards, a chain-extension reaction with hexamethylene diisocyanate (HDI) was carried out to prepare (PLA-b-PB-b-PLA)(n) multi-block copolymers with enhanced molecular weight. The structures and properties of these block copolymers were then characterized by gel permeation chromatography (GPC), nuclear magnetic resonance (NMR), differential scanning calorimetry (DSC), atomic force microscope (AFM) and Fourier-transform infrared (FTIR). Toughening effect of the (PLA-b-PB-b-PLA)(n) multiblock copolymers on biodegradable poly(l-lactide) (PLLA) film was investigated and the blended film with higher (poly(d-lactide)-b-poly(butadiene)-b-poly(d-lactide))(n) (PDLA-b-PB-b-PDLA)(n) loading (15 wt%) exhibited better toughness nearly without loss of the tensile strength. The mechanical properties of the (PLA-b-PB-b-PLA)(n)/PLLA blended film were proved to be influenced by the different isomers of PLA and rubbery PB chains.