Time-Temperature Superposition in Heterophase Block Copolymers
The viscoelastic behavior of a styrene-butadiene-styrene block copolymer cast from several different solvents was studied in order to examine the validity of the time-temperature superposition principle in heterophase polymers. It is found that stress-relaxation isotherms over a wide temperature range can be easily superposed into smooth master curves. The master curves compare favorably with other mechanical data determined at long times and at high frequencies. The shift factors used in superposition can be rationalized by an additive model. However, it is pointed out that this apparent thermorheological simplicity is strictly valid only in the region where one of the relaxation mechanisms dominates. Consequently, only those portions of the master curve that meet this criterion are expected to be useful. Dynamic mechanical data illustrating the effect of multiple relaxations are presented.
KeywordsBlock Copolymer Master Curve Methyl Ethyl Ketone Glassy Phase Shift Factor
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