Effect of Microdomain Structures on Mechanical Properties of Polystyrene-block-Polyethylenebutylene-block-Polystyrene Triblock Copolymer Films

Abstract

We report here effects of microdomain structures on the mechanical properties of polystyrene-block-polyethylenebutylene-block-polystyrene (SEBS) triblock copolymers. Microdomain structures were analyzed by the small-angle X-ray scattering technique and the mechanical properties were evaluated by the viscoelastic measurements. Two kinds of SEBS samples were used, which have similar molecular weights but different compositions. One of them having φ_ps (volume fraction of polystyrene) of 0.16 underwent transition from spherical to cylindrical morphology when an as-cast film from its heptane/methylene chloride (1/1 by volume) solution was annealed at 150°C which is above the glass transition temperature of PS (polystyrene). Another SEBS sample having φ_ps = 0.54 exhibited lamellar ordering when an as-cast film was annealed at 150°C According to these structural transformation, mechanical properties changed. Especially, the storage moduli of the annealed films around 25°C increased twice as big as the as-cast films. This result correlates well with generation and development of continuity of the glassy PS microdomains in SEBS16 and SEBS53, respectively.