Modifications of traditional membrane support assemblies are described that permit accurate measurement of gas permeability coefficients for side-chain crystalline poly(n-alkyl acrylate)s or poly(n-alkyl methacrylate)s above and below the melting point. These modifications address the problems associated with the very brittle nature of these materials below the melting point and their fluid-like nature above the melting point. An Anopore(TM) porous ceramic disc coated with poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) masked with aluminum tape on the downstream surface was the support ultimately chosen to perform these measurements. The problems and concerns leading to the choice of this assembly are described. Crystallite orientation in solvent cast films of the side-chain crystalline polymers is demonstrated by wide-angle X-ray diffraction (WAXD). Melting the film and recrystallization on cooling effectively eliminates such orientation.