Abstract: A model was formulated that contained oxygen, nitrogen molecules and PMMA polymer chains. The diffusion of the mixed gas (oxygen and nitrogen) in PMMA was simulated at different temperatures or pressures. It was found that the diffusion coefficients of oxygen and nitrogen in PMMA increased with increasing temperature and pressure and finally reached a platform. The interaction between the two kinds of molecules during the diffusion was also discussed. Different kinds of molecules had a synergistic effect during the diffusion, the diffusion coefficient of the gas in the mixed gas system was greater than that in the pure gas system.

Key words: packing stage, gas diffusion, molecular dynamics, polymethyl methacrylate