MICROPHASE SEPARATION OF A SYMMETRICAL POLY(STYRENE-B-PARAMETHYLSTYRENE) DIBLOCK COPOLYMER

The microphase separation in a symmetric diblock copolymer consisting of polystyrene and polyparamethylstyrene has been studied by small-ang le neutron scattering. The observed peak changes with temperature in i ntensity, shape and position. The peak position shifts at the micropha se separation transition temperature T(MST) by approximately 7%. Also from a peak intensity analysis we determine T(MST) at approximately 18 0-degrees-C. The shape of the peak change at T(MST) and the indication of a second-order peak is observed, characteristic of a lamellar phas e in the ordered regime. Intensity does not vanish for q --> 0, but ha s a temperature-dependent level. Results are discussed with respect to recent computer simulations and theoretical approaches. A simple mean -field picture is not consistent with the data.