This work reports the permeation of argon through membranes prepared from poly(pentaerythritoltribenzoate acrylate) (PPTBA) (IUPAC name poly[1-(3-benzoyloxy-2,2-dibenzoyloxymethylpropyloxy)-2-propen-1-one]). The permeation measurements were performed in the vicinity of the glass transition temperature of the membranes (48 degrees C). The permeation coefficient only shows a slight dependence on temperature in the glassy state, but it undergoes a sharp increase with temperature in the rubbery state. The results for the diffusion coefficient do not show a definite temperature dependence in the glass-rubber transition. As expected, the solubility of the gas in the membrane is higher in the rubbery state than in the glassy state. The diffusion coefficient was calculated theoretically by using the Transition-State Approach which assumes that the diffusant path is independent of the structural relaxations in the polymer matrix. Reasonably good agreement between the simulated and the experimental values of the diffusion coefficient was obtained in the range of temperatures from 40 to 60 degrees C in which the measurements were performed.