Synthesis of Poly(L-lactide)-b-poly(ethylene glycol)-b-poly(L-lactide) Bioplastic with Bio-based Isosorbide Diester

In situ chain-extended poly(L-lactide)-b-poly(ethylene glycol)-b-poly(L-lactide) (PLLA-PEG-PLLA) block copolymers synthesized by ring-opening polymerization of L-lactide in the presence of chain extender were more flexible than PLLA. However, flexibility of PLLA-PEG-PLLA requires further improvement to broaden its applications. Herein, plasticization of PLLA-PEG-PLLA with an isosorbide diester bio-based plasticizer (5-20 %wt) is described. PLLA/isosorbide diester blends were also prepared for comparison. The blends prepared via melt blending revealed that isosorbide diester showed good phase compatibility with both the PLLA and PLLA-PEG-PLLA. The addition of isosorbide diester significantly enhanced plastic deformation of cryo-fracture surfaces for PLLA-PEG-PLLA-based blends whereas the plastic deformation was started at 20 %wt isosorbide diester for PLLA-based blends. Crystallization properties and thermal stability of PLLA-PEG-PLLA greatly improved after the addition of isosorbide diester but did not increase the thermal stability for PLLA-based blends. The strains at break of the PLLA-PEG-PLLA-based blends containing 5 %wt, 10 %wt and 20 %wt isosorbide diester were 89.9%, 145.3% and 110.5%, respectively: these were higher than the pure PLLA-PEG-PLLA (59.8%). The plastic deformation, thermal stability and strain at break of the PLLA-PEG-PLLA-based blends increased greatly with content of isosorbide diester, reaching a maximum at 10 %wt isosorbide diester. Therefore, isosorbide diester is promising as a bio-based plasticizer for PLLA-PEG-PLLA to produce highly flexible PLLA-based bioplastics.