DIRECT MEASUREMENT OF CHAIN STRETCHING IN DIBLOCK COPOLYMERS AT THE MICROPHASE SEPARATION TRANSITION

The microphase separation transition (MST) in poly(styrene-b-paramethy lstyrene) diblock copolymers is investigated by small-angle neutron sc attering. In a blend of fully deuterated and protonated chains the con formation of single chains as a function of temperature is obtained. W e observe chain stretching at MST of approximately 5% going from the d isordered to the ordered regime. Directly determined radii of gyration are compared to calculated ones, which are obtained from an analysis of the Leibler-peak position. Results are discussed in the context of recent theories and computer simulations.