Case II Diffusion Behavior in Alcohol Absorption by Poly (methyl methacrylate)

The structure and properties of alcohol and the ambient temperature causing the case II diffusion were investigated by studying the behavior of alcohol absorption by poly (methyl methacrylate) (PMMA). The case II type of diffusion was newly confirmed to take place for the cases of 1-propanol, 1-butanol, and 2-methyl-1-butanol; methanol, ethanol, and 2-puropanol have already been known to show the case II behavior for PMMA. The lower temperature for the appearance of case II diffusion was raised with increasing the molar volume of alcohol. The absorption rate was decreased with an increase in the molar volume, as with the Fickian diffusion observed for other polymerreagent systems. Linear propanol and linear butanol showed greater absorption rate and less equilibrium solubility than the branched molecules. The equilibrium solubility of linear alcohol was constant or somewhat decreased with increasing the molar volume. Kramer's theory on the case II diffusion, which was modified by introducing the volume strain rate, was shown to provide good expressions for the absorption behavior of methanol by PMMA, but one should compare with the behavior of other alcohols for proving the adequacy.