Effect of film thickness on the changes in gas permeability of a glassy polyarylate due to physical aging Part I. Experimental observations

The effects of thickness (0.25-33 mu m) and aging time on the gas permeation properties of films formed from a glassy polyarylate made from bisphenol-A benzophenone dicarboxylic acid were examined. Evidence is presented which shows that physical aging is responsible for a significant decrease in gas permeability with time following quenching the polymer from above its glass transition temperature; the rate of change is greater for the thinner films. Two methods of determining accurate film thicknesses were used to obtain absolute permeability coefficients. The importance of the permeation protocol on the aging rate was examined, and a reversal of the aging process was demonstrated by annealing the aged film above the T-g. These results indicate that physical aging occurs by two distinct simultaneous mechanisms: one which is thickness dependent and another that is not. (C) 1999 Elsevier Science Ltd. All rights reserved.