Abstract: The diffusion behavior of the mixture of O2/N2 in PMMA melts during the packing stage of injection molding was studied. According to the characteristics of injection molding, the diffusion of the gas in the packing stage was simplified asaquasistatic diffusion. Establishing a kind of a diffusion mappingmodel was formulated made up of O2/N2 gas and ten isotactic PMMA chains whose degree of polymerization was 10.By energy minimization and annealing algorithm, this diffusion model achieved an energy initialization.Based on the COMPASS force field,the diffusion of the mixture gas of O2/N2 in PMMA melts was simulated successfully. The result was that the diffusion coefficients of O2 and N2 increased with increasing temperature, and at the same temperature, the diffusion of O2 was easier than N2. Plotting lg(MSD) against lg(t) for O2 and N2, both the slopes of the curves were close to 1 at different temperatures, which conformed to the diffusion mechanism of Einstein. In addition, the activation energy of diffusion of N2 was higher than that of O2.

Key words: injection molding, holding pressure, oxygen, nitrogen, molecular dynamics, diffusion