LOCAL AND GLOBAL CHAIN DYNAMICS IN DIBLOCK COPOLYMER MELTS

Photon correlation spectroscopy in the depolarized mode and dielectric relaxation spectroscopy were employed to investigate local and global chain motions in poly(styrene-b-1,4-isoprene) diblock copolymer melts near the order-to-disorder transition (ODT). The presence of two distinctily different segmental orientation processes and the temperature dependence of the width of the slow relaxation function in the disordered state imply strong composition fluctuations in calorimetrically and rheologically homogeneous diblocks. The estimated amplitudes of composition fluctuations increase with the proximity to the ODT. The polyisoprene subchain orientation is characterized by a single broad distribution of relaxation times above the ODT, that apparently senses an average friction. This is due to the fact that the end-to-end vector orientations sample fluctuations at a different length scale than segmental orientations do.