SELF-DIFFUSION OF A POLYSTYRENE-POLYISOPRENE BLOCK-COPOLYMER

Forced Rayleigh scattering (FRS) has been used to measure the self-dif fusion coefficient, D, of a lamellar-forming polystyrene-polyisoprene diblock copolymer (M(PS) = 1.0 x 10(4), M(PI) = 1.3 x 10(4)) as a func tion of temperature. The measurements traverse the order-disorder tran sition (ODT), which occurs at 160 degrees C. There is no obvious chang e in either D or the temperature dependence of D at the ODT, in agreem ent with measurements on several other systems. Electron microscopy co nfirms that the sample in the ordered state is quenched, with no long- range orientation of lamellae, and a typical grain size well below 1 m u m. In contrast to previous measurements on a similar styrene-isopren e diblock, these FRS signals are well-described by single exponential decays; this may be largely attributed to differences in average grain size. The temperature dependence of D is modeled with several empiric al expressions, based on the known monomeric friction factors for pure polystyrene and pure polyisoprene, but without quantitative success. These results underscore the need for a greater understanding of the c omposition and temperature dependences of local friction in polymer mi xtures. (C) 1996 John Wiley & Sons, Inc.