Viscoelastic and Dielectric Properties of A-B-A Type Block Copolymers

Abstract

The viscoelastic and dielectric properties of two A-B-A type block copolymers were determined. One contains styrene-butadiene- styrene (SBS) blocks and the other styrene-isoprene-styrene (SIS) blocks. Samples were prepared by casting from solutions of these polymers in benzene/heptane, carbon tetrachloride and methylethyl- ketone/tetrahydrofuran. The viscoelastic behavior of SIS block copolymers is apparently unaffected by the casting solvent, while that of the SBS block copolymers is similar from the former two solvents but drastically modified for the MEK/THF-cast sample. Shift factors utilized in constructing the viscoelastic master curves were found to obey the WLF equation as modified by Shen and Kaelble, except for the MEK/THF-cast SBS block copolymer. Dielectric loss curves were obtained over an extended frequency range. For comparison, the mechanical loss curve for a CCl4-cast SBS block copolymer was computed from master curve by linear programming. In both cases the only observed loss peaks were those resulting from the primary glass transitions of the respective blocks. No peak was found in the intermediate temperature range that may be attributable to the “mixed” regions.