Synthesis of Novel Silicon-Containing Amphiphilic Diblock Copolymers and Their Self-Assembly Formation in Solution and at Air/Water Interface

Abstract

Amphiphilic block copolymers, poly(1,1-dimethylsilacyclobutane-block-2-hydroxyethyl methacrylate) (poly(DMSB-b-HEMA)), poly(1,1-diethylsilacyclobutane-b-2-hydroxyethyl methacrylate) (poly-(DESB-b-HEMA)), and poly(1,1-dibutylsilacyclobutane-block-2-hydroxyethyl methacrylate) (poly(DBSB-b-HEMA), were synthesized by a living anionic polymerization, and their self-assembled structures were investigated. Small-angle X-ray scattering (SAXS) analysis suggested that the block copolymers formed micelles in methanol and that the aggregation number of the micelles increased with the increase of polysilacyclobutane (polySB) content and number of carbon atoms in the alkyl groups on silicon. A remarkable temperature dependence of the micelle structure of poly(DMSB-b-HEMA) was observed. Small-angle neutron scattering (SANS) revealed that the block copolymer formed spherical micelle with a core-shell structure above room temperature and a disklike micelle below room temperature. The surface pressure-area per molecule (π-A) isotherm of spread copolymer indicated that poly(SB-b-HEMA)s formed a thin layered film on the water surface. The π-A isotherm of the poly(DMSB-b-HEMA) spread layer also exhibited a characteristic temperature dependence. Direct X-ray reflectivity (XR) measurement on the water surface indicated that the block copolymers formed a monolayer with uniform thickness and smooth interfaces at medium surface pressure around 30 mN/m. In the case of poly(DBSB-b-HEMA), on the other hand, it was supposed that another layer with a large thickness appeared in the monolayer at a higher surface pressure than 35 mN/m. Atomic force microscopy (AFM) measurement of poly(DBSB-b-HEMA) film deposited on a glass plate at that surface pressure supported the existence of a thicker layer in addition to monolayer.