RHEOLOGICAL STUDIES ON THE PHASE DISSOLUTION IN A BLOCK-COPOLYMER

The microphase transition in a styrene-butadiene-styrene triblock copo lymer was studied by rheometric mechanical spectroscopy. A high-temper ature-melt rheological transition from the highly elastic, nonlinear v iscous behavior typical of a multiphase structure to linear viscous be havior with insignificant elasticity typical of a single-phase structu re was observed. The transition temperature is determined according to the discontinuity of the rheological properties across the transition region, which agrees well with the results obtained from the small an gle X-ray scattering data and the expectation of the random phase appr oximation theory. Maybe for the first time, microphase dissolution was investigated theologically. The storage modulus (G') and the loss mod ulus (G '') increase with time during the process. An entanglement flu ctuation model based on the segmental density fluctuations is presente d to explain the rheological behavior in this dissolution process. (C) 1997 John Wiley & Sons.