Dynamic viscoelastic behavior of ABA block polymers and the nature of the domain boundary

Abstract

Abstract Dynamic viscoelastic properties of block copolymers of styrene with butadiene or isoprene are consistent with the growth of a diffuse interphase or interlayer as block lengths decrease. Under the conditions of the present study the interlayer does not lead to a secondary loss maximum between the two domain glass transitions. The pattern of shifts of the loss maxima characteristic of the domain T g 's suggests strongly that the interlayer composition profile must be asymmetric with an average volume composition rich in styrene. Typical block polymer viscoelastic behavior is observed even beyond the point at which the interlayer attains 100% of the polymer volume. Such block polymers no longer contain compositionally pure phases, but are visualized as retaining a residual domain structure in which composition fluctuates between ever narrowing limits as blocks become shorter, approaching homogeneity and the mechanical behavior of random copolymers.