INTERACTIONS OF SUBSTITUTED BENZENES WITH ELASTOMERS

The effects of polymer structure and penetrant molecular size on sorption and diffusion of substituted benzenes (aromatics) with commercial elastomers such as neoprene, ethylene-propylene-deine terpolymer, styrene-butadiene rubber, nitrile-butadiene rubber and natural rubber have been investigated in the temperature interval of 25-60-degrees-C. The rate-of-sorption behaviour deviates from the Fickian mechanism. The equilibrium sorption of the sorbents decreases linearly with increasing penetrant molecular size. At about 55-60 mol% uptake, the sorbed concentration levels off. Diffusion coefficients decrease with increasing molecular weight of the penetrants. It is suggested that the hindered chain segmental motion contributes to the overall sorption in addition to strictly thermodynamic considerations. Free-volume concepts can be used to explain the diffusion mechanism through rubbery polymers. Effective values of the molar mass between crosslinks computed from the Flory-Rehner theory appear to vary widely with different liquids and elastomers.