The effects of tacticity of poly methyl methacrylate (PMMA) on the morphology and size distribution of free volume and gas molecules transport through PMMA matrix were conducted by molecular simulation techniques. How the spatial structure of PMMA affects the glass transient temperature T-g of stereoregular PMMA membranes and the solution and diffusion mechanisms in the stereoregular PMMA membranes were conducted by molecular simulation techniques and were compared with experimental data. The polymerchains conformation, gas diffusion mechanism, the time course of the accessible free volume, free volume size distribution, free volume morphology and glass transient temperature, in the various stereoregular PMMA were obtained by a molecular dynamics simulation technique, while the g-as solubility in different stereoregular PMMA was calculated by a Monte Carlo technique. A comprehensive comparison of the physical and transport properties of the stereoregular PMMA membranes between simulated and experimental results are provided based on a microscopic interpretation of chain flexibility, free volume morphology and size distribution of free Volume in the stereoregular PMMA membranes and gas molecule transport mechanisms through the stereoregular PMMA membranes. (c) 2005 Elsevier B.V. All rights reserved.