The transport of argon in membranes of poly(bisphenol A carbonate-co-4,4'-(3,3,5-trimethylcyclohexylidene)diphenol carbonate), under differences of pressure, Deltap, lying in the interval 8-160 cmHg and in the temperature range 30-55 degreesC, is described. The experimental values of the permeability and diffusion coefficients at 30 degreesC and Deltap = 76 cmHg are 4.5 barrers and 3.0 x 10(-8) cm(2) s(-1), respectively. The values of these parameters are nearly independent of the differences of pressure between the two faces of the membrane. The permeability and the diffusion coefficients obey Arrhenius behavior with activation energies of 3.7 and 6.7 kcal mol(-1), respectively. The permeation of argon in the membranes was simulated using the transition-state approach. Good agreement between simulated and experimental results is found by assuming that the polymer chains of the membrane fluctuate around equilibrium positions with a root-mean-square deviation Delta of 0.3 Angstrom at 40 degreesC. Comparison of the experimental and simulated values for the diffusion and solubility coefficients suggests that the value of Delta increases with temperature at a rate of 0.005 Angstrom K-1.