Rheological and Dielectric Behavior of Dipole-Inverted (SIS)p-Type Multiblock Copolymers: Estimates of Bridge/Loop Fractions for Respective I Blocks and Effect of Loops on High Extensibility of Bridges

Abstract

A series of symmetric styrene− (S−) cis-isoprene (I) multiblock copolymers of (SIS)p-type (p = 1, 2, 3, and 5 corresponding to tri-, penta-, hepta-, and undecablock) was synthesized with an anion-coupling method and their rheological and dielectric behavior was examined in n-tetradecane (C14), a solvent dissolving the I block and precipitating the S block. The molecular weights of the constituent blocks were almost identical for these copolymers, and a particular I block(s) of respective copolymers had symmetrically once-inverted type-A dipole while the remaining I blocks had noninverted dipoles. At 20 °C, the (SIS)p/C14 systems with the (SIS)p concentration of 40 wt % formed a bcc lattice of glassy, spherical S domains (as confirmed from SAXS) and exhibited the gel-like elasticity. This elasticity was sustained mainly by the bridge-type I blocks connecting the S domains and partly by the coexisting loop-type I blocks. The dielectric loss (e‘ ‘) data exclusively detected the fluctuation of the midpoint of...