VISCOELASTIC BEHAVIOR OF A HOMOGENEOUS POLYSTYRENE-BLOCK-POLYISOPRENE-BLOCK-POLYSTYRENE COPOLYMER

A polystyrene-block-polyisoprene-block-polystyrene (SIS) copolymer having block molecular weights of 3900S-93300I-3900S was synthesized via anionic polymerization, and its linear dynamic viscoelastic properties (dynamic storage and loss moduli, G'(omega) and G"(omega), as functions of angular frequency omega) were measured at various temperatures, using a cone-and-plate rheometer. Plots of log G' versus log G" were found to be independent of temperature in the range from 50 to 150-degrees-C, leading us to conclude that the block copolymer had no microdomain structure at T greater-than-or-equal-to 50-degrees-C. Independent study by small-angle X-ray scattering confirmed that the SIS block copolymer indeed had no microdomain structure (i.e., homogeneous) at T greater-than-or-equal-to 30-degrees-C.