PROBE DIFFUSION IN HOMOGENEOUS DIBLOCK COPOLYMERS

Forced Rayleigh scattering was used to investigate the diffusion of a photoreactive dye molecule in two homogeneous poly(styrene-b-isoprene) (SI) diblock copolymers with overall molecular weights of approximate ly 2000. Although diffusion rates were intermediate to TTI transport i n homopolymer polystyrene (PS) and polyisoprene (PI), system dynamics appear to be largely dictated in each case by the PI block. The size o f the polymer jumping unit, on the other hand, is evaluated from a fre e-volume analysis of the data, and is found to be governed predominant ly by the PS component of the copolymer. The mechanism for tracer diff usion in low-molecular-weight block copolymers appears analogous to tr ansport in a high molecular weight SI diblock copolymer (M-n = 13,600) that has been solvated sufficiently in toluene to be microstructurall y disordered. (C) 1998 John Wiley & Sons, Inc.