Stereocomplexation and mechanical properties of polylactide-b-poly(propylene glycol)-b-polylactide blend films: Effects of polylactide block length and blend ratio

In the present work, poly(propylene glycol) (PPG) was block copolymerized to form polylactide-poly(propylene glycol)-polylactide (PL-PPG-PL) triblock copolymers for preparing flexible stereocomplex PL (scPL) blend films. The scPL blend films were prepared by solution blending of poly(L-lactide)-PPG-poly(L-lactide) (PLL-PPG-PLL) and poly(D-lactide)- PPG-poly(D-lactide) (PDL-PPG-PDL) triblock copolymers before film casting. The influences of PL end-block lengths (2 x 10(4) and 4 x 10(4) g/mol) and blend ratios (75/25, 50/50 and 25/75 W/W) on the stereocomplexation and mechanical properties of the blend films were evaluated. From DSC and WAXD results, the 50/50 blend films had complete stereocomplexation. Phase separation between the scPL and PPG phases was not observed from their SEM images. The tensile stress and elongation at break increased with the sterecomplex crystallinities and PL end-block lengths. The PPG middle-blocks enhanced elongation at break of the scPL films. The results showed that the PL-PPG-PL triblock structures did not affect stereocomplexation of the PLL/PDL block blending. In conclusion, the phase compatibility and flexibility of the scPL films were improved by PPG block copolymerization.