| Abstract: | Permeation of eight gases (He, Ne, Ar, Kr, O2, N2, CO2, and CH4) in three isomeric poly(vinyl methylbenzoates) was measured by the time-lag method, and the effects of the shape of side groups on gas transport in the polymers were investigated. The p-methylphenyl side group of poly(vinyl p-methylbenzoate), which increases both interchain and intrachain distances, caused an increase in gas diffusivity. The diffusivity and density data were consistent with free volume theory. Two other isomeric polymers, poly(vinyl o-methylbenzoate) and poly(vinyl m-methylbenzoate), had lower gas diffusivities than poly(vinyl p-methylbenzoate) and poly(vinyl benzoate). The o-methyl and m-methyl groups on the phenyl ring were found to hinder gas diffusion, i.e., decrease the free volume. In contrast, the solubility of the gases in all these polymers was similar because of their similar chemical structures. The effects of hydroxyl groups also were investigated by the use of poly(vinyl m-methylbenzoate) containing a small number of vinyl alcohol units. The decrease in gas diffusivity was attributed to the decrease of free volume due to hydrogen bonding, but the change of gas solubility was still negligible. |
