Detection of the glass relaxation process of the PS-phase in block copolymers

The relaxation behavior of the glass process of the polystyrene (PS) phase in three different types of block copolymers has been investigated. Four triblock copolymers are used, namely, two styrene–butadiene–styrene (S–B–S), styrene–styrene butadiene–styrene (S–SB–S) and styrene–ethylene butylene–styrene (S–EB–S). The materials were crosslinked by means of dicumylperoxide (DCUP) with concentrations up to 10 phr, i.e. 10 g of DCUP per 100 g of the polymer. Dynamic mechanical measurements have been done for the complex shear compliance in wide temperature and frequency windows, 30–150 °C and 10−3–10 Hz, respectively. Complete master curves have been constructed for all samples and analyzed using Cole–Cole function. It is observed that crosslinking reduces the relaxation strength of the low frequency process much more than that of the high frequency process. Therefore, the glass relaxation process of the PS-phase can be easily detected in the crosslinked samples. The relaxation frequency of the maximum of the glass relaxation process of the PS-phase is found to be independent of the crosslinking concentration. The relaxation behavior of block copolymers with respect to crosslinking is compared to styrene butadiene rubber (SBR) statistical copolymer. A method to detect the glass transition temperature (Tg) of the investigated block copolymers is suggested.