SAXS and rheological studies on the order-disorder and order-order transitions in mixtures of polystyrene-b-polyisoprene-b-polystyrene and low molecular weight PS

The order-disorder and order-order transitions (ODT and GOT) of a series of mixtures of polystyrene-block-polyisoprene-block-polystyrene copolymers (SIS), V4411D (f(PS) = 0.377) and V4113 (f(PS) = 0.131), and low molecular weight PS homopolymers with different molecular weights have been investigated by using both small-angle X-ray scattering (SAXS) and rheological measurements. ODT temperatures determined from the discontinuous change in 1/I-max and sigma q(2) vs 1/T plots were found to be in reasonable proximity to the ones determined from the discontinuous change in log G' vs T plots. OOT was also identified for pure V4113 and a few of its mixtures with PS homopolymers, as evidenced from SAXS measurements. While the phase behavior including ODT of V4411D/PS mixtures was in good agreement with theoretical predictions, that of V4113/PS mixtures showed unusual behavior. This was attributed to the change in PS homopolymer distribution in the microdomain with the addition of low molecular weight PS homopolymer to the SIS triblock copolymer.