DIELECTRIC-RELAXATION BEHAVIOR OF STYRENE ISOPRENE DIBLOCK COPOLYMERS - BULK SYSTEMS

Dielectric relaxation of polystyrene-polyisoprene (SI) diblock copolymers was examined in the bulk state at low temperatures. Under such conditions microphase separation took place and PS blocks form glassy domains, and thus only the motion of PI blocks anchored on the domain boundary and confined in their own lamellae was observable. The dielectric normal modes of such end-grafted PI blocks due to their global motion were seriously affected by the confinements in microdomains: The normal modes were significantly retarded and broadened as compared to those of free homo-PI chains. To interpret such differences, spatial confinement as well as thermodynamic confinement (to keep uniform segment density) in microdomains was considered. Comparison of the normal modes between block- and homo-PI chains both mixed with (dielectrically inert) polybutadiene blocks in lamellae suggested that the effects of the confinements were interdependent and much larger for PI blocks than for homo-PI chains, probably because the requirement of uniform density affects the chain configuration much more seriously for the former with fixed ends than for the latter without such ends.