Polymer Chemistry

Biography

Biography: Yoshiharu Kimura

Abstract

Various block copolymers comprising enantiomeric polylactides (PLLA and/or PDLA depending on the enantiomeric chains) and poly(oxyethylene) (PEG) were prepared to analyze the structural effects on the formation of core-shell nanoparticles in aqueous media. It was found out that the micelle particle structure and stability can be correlated with the position of streocomplex (sc) crystallization inside the micelle cores. This finding gives an insight into the dynamic and static mechanisms of macromolecular aggregation and ordering, particularly, into the process of sol-gel formation in the mixed micellar solution of the enantiomeric PEG-PLA block copolymers. Also we succeeded in synthesizing several copolymer mixtures of furan-terminated diblock copolymers (F-PEG-PLA) and triblock copolymers (PLA-PEG-PLA) having different compositions by ROP of L- and D-lactides using partially furanylated PEGs as the macro initiators. Each of the copolymer mixtures obtained was dispersed into an aqueous medium to prepare mixed micelle solutions of the enantiomeric copolymer mixtures in the presence and absence of a coupling agent 1,8-bis(maleimido)diethylene glycol (BMG). The BMG-added mixed micelle solutions turned to gel states having higher storage moduli (11 kPa) than their corresponding BMG-free micelle solutions. The former systems were thought to be controlled by the dual cross-linking mechanisms for the gel formation; physically by sc formation between the enantiomeric PLA block chains and chemically by Diels-Alder coupling between the furanyl terminals on PEG blocks and BMG. These sol-gel systems are not only interesting in terms of tuning the self-assembling micelle formation and sol-gel transition but also promising to provide injectable scaffolds in the tissue engineering.