Stereocomplexation of high molecular weight enantiomeric poly(lactic acid)s enhanced by miscible polymer blending with hydrogen bond interactions
Abstract A feasible approach is proposed to enhance the ability of stereocomplex (SC) crystallization and depress the homocrystallization in high molecular weight (HMW) poly( l lactic acid)/poly( d lactic acid) (PLLA/PDLA) racemic blends by miscible polymer blending with hydrogen bond interactions. Poly(vinyl phenol) (PVPh) is selected as a model polymer and blended with PLLA and PDLA at different compositions. Crystallization kinetics, polymorphic crystalline structure, and lamellae morphology of PLLA/PDLA/PVPh ternary blends were investigated and compared with the PLLA/PDLA racemic blend. The crystallization rate and spherulitic growth rate of PLLA/PDLA blends are decreased after blending with PVPh. However, the content of SCs in the ternary blends are enhanced under the nonisothermal and isothermal crystallizations at different temperatures. SCs are predominantly generated in the PLLA/PDLA/PVPh blends with relative high PVPh content. Long periods of both SCs and homocrystallites increase with increasing the PVPh content, indicating that the noncrystallizable PVPh component is segregated into the interlamellae region of crystalline phase. It is proposed that the preferred SC crystallization of PLLA/PDLA blends upon miscible blending with PVPh is caused by the increased intermolecular interactions, decreased diffusion pathway of enantiomeric chains, and the decreased melting point.