Abstract
Thermomechanical spectra of poly(styrene-b-butadiene) copolymers were obtained at 110 Hz and between −120 and 120°C. The molecular parameters studied were the styrene content (35%–45%) and, at constant composition (39% styrene), the length of the copolymer blocks. The films studied were cast from selective solvents, methyl ethyl ketone (MEK), cyclohexane, and toluene, a common solvent. MEK- and toluene-cast films were quite similar in their dynamic viscoelasticity and more rigid than the corresponding cyclohexane-cast films. Solvent differentiation was more evident at the higher styrene content. No evidence of a relaxation due to a mixed interphase was obtained. At constant composition a morphological transformation takes place when the length of the blocks exceeds a certain limit; this affected the dynamic modulus of the cyclohexane-cast films. The results were analyzed using two-phase models proposed by the composite theory. For some samples results on the effect of annealing and prestretching are also reported.
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