Diffusion and Sorption of Cyclohexane Vapor in SBS and SBR Copolymers.

Diffusion and sorption of cyclohexane vapor in styrene-butadiene copolymers were used to study the morphology of an SBS triblock copolymer 29.3 wt styrene cast from different solvents. The weight gain or loss of this SBS and several SBR 5, 23, 45 and 85 wt S content samples were continuously monitored at 40 C and at penetrant pressures of 30, 60, 90 and 120 torr. Significant differences exist in the equilibrium sorption among the different samples. Possible reasons for this observation are explored. The one corroborated by dynamic mechanical measurements attributes the differences to varying interphase volume fractions. The interphase region separating the PB and PS phases in SBS was assumed to be a continuous profile of equivalent SBR with different S contents. Experimental results, coupled with simple calculations, indicated that the overall interphase volume fraction in the SBS are 0.28 for the MEKTHF-cast 19 volume ratio of MEK and THF sample, 0.15 for the toluene-cast sample, and 0.04 for the cyclohexane-cast sample.