INVESTIGATION OF THE TLL(GREATER-THANTG) RELAXATION IN HOMOPOLYMERS AND BLOCK COPOLYMERS OF STYRENE BY TORSIONAL BRAID ANALYSIS

Investigation of the Tu (>Tg) relaxation in amorphous polymers of styrene by the technique of torsional braid analysis is reviewed. For the most part the relaxation behaves like the glass transition (Tg) in its dependence on molecular weight, on average molecular weight in binary polystyrene blends, and on composition in a polystyrene homogeneously plasticized throughout the range of composition. Diblock and triblock copolymers also display a T > Tg relaxation above the Tg, of the polystyrene phase. Two results in particular suggest that the Tu relaxation is molecularly based. (1) The Tu temperature is determined by the number average molecular weight for binary blends of polystyrene when both components have molecular weights below Mc. (the critical molecular weight for chain entanglements). (2) Homopolymers, and diblock and triblock copolymers of styrene, have a T > Tg relaxation at approximately the same temperature when the molecular weight of the styrene block is equal to that of the homopolymer. Copyright © 1979 Society of Plastics Engineers, Inc.