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 permeatio n 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 glas s transition temperature; the rate of change is greater for the thinner fil ms. Two methods of determining accurate film thicknesses were used to obtai n absolute permeability coefficients. The importance of the permeation prot ocol on the aging rate was examined, and a reversal of the aging process wa s demonstrated by annealing the aged film above the T-g. These results indi cate that physical aging occurs by two distinct simultaneous mechanisms: on e which is thickness dependent and another that is not. (C) 1999 Elsevier S cience Ltd. All rights reserved.