Effects of solvent and thermal annealing on the dielectric properties and morphology of dimethyl siloxane/α-methylstyrene block copolymers

Abstract

The dielectric and morphological properties of a series of 9/1 poly(dimethyl siloxane) PDMS)/poly(α-methylstyrene) (PαMS) block copolymers and a 6/4 PDMS/PαMS block copolymer have been determined as a function of solvent casting and thermal treatment. Transmission electron microscope ( TEM) results show better phase separation as a function of thermal annealing and casting from cyclohexane, a PDMS preferential solvent. Dielectric studies in the temperature region of the PDMS glass transition are consistent with the TEM results and are interpreted in terms of a most probable distribution of PDMS/PαMS mixed states. When the PDMS segment molecular weight is less than the critical molecular weight, thermal annealing of the solvent cast samples produces a phase separated sample exhibiting the T g of PDMS as well as a mixed phase. Thermal annealing of samples with the PDMS segment molecular weight greater than the critical molecular weight produces little change in the mixed structure and the dielectric data. All samples have PαMS segment molecular weights less than the critical molecular weight. The observed changes are interpreted in terms of kinetic effects associated with polymer melt viscosity (critical molecular weight) and expected mixing of the two components.