Elongational Flow-induced Crystallization of Poly(_L-lactic acid) Telechelic Ionomers

In this study, we prepared unentangled and slightly entangled poly(_L-lactic acid) telechelic ionomer samples (M_n=5 and 16 kg/mol) based on sodium sulfonate groups. The telechelic samples exhibit extremely slow crystallization kinetics below the melting temperature T_m and above the glass transition temperature T_g, which enables us to examine the linear viscoelasticity of the ionomer melt samples therein. The application of either the shear flow (at 85 °C) or elongational flow (between 70 and 90 °C) strongly accelerates the crystallization, leading to strong strain hardening and formation of highly oriented α crystals. Depending on the relative average rates of the strain-induced dissociation and strain-induced crystallization, the stress evolution can be classified into two cases, and the critical work for strain-induced crystallization is higher in case where the strain-induced dissociation occurs earlier than the strain-induced crystallization.