Effect of Block Position on the Dynamics of the Glass Processes in Carbonate/Styrene Triblock Copolymers, CSC and SCS

Abstract

Molecular dynamics of specially prepared triblock copolymers of polystyrene and polycarbonate were studied by dielectric spectroscopy over wide ranges of frequency; 10-1 - 105 Hz and temperature; 50-200°C. Two block copolymers are used in the current investigation; carbonate-styrene-carbonate, CSC and styrene-carbonate-styrene, SCS, which have blocks with the same molecular weights but with different positions. The dielectric relaxation spectra and d.s.c scans showed that these block copolymers CSC and SCS exhibit two relaxation processes corresponding to the glass transitions of the two microseparated PS- and PC-phases. It is surprising to find that the molecular dynamics of either PS- or PC-blocks are different in CSC and SCS and also differ from the dynamics of the corresponding homopolymers with same molecular weight, i.e. the molecular dynamics of the blocks depends on their position within the chain. The results are assessed and discussed in terms of the different factors that could affect the glass transition and its dynamics for different blocks; namely: the number of free end groups per block and the morphological confinement that influence the size of the cooperative regions responsible for the glass transition.