Estimating diffusion coefficients for small molecules in polymers and polymer solutions

The diffusion coefficient for small molecules (solvent or monomer) through polymer solutions in the vicinity of the glass transition are known to chan ge by as much as six orders of magnitude with only a small change in polyme r concentration. Experimental measurements are difficult in this region and consequently there are data for only a limited number of systems. A rather simple method to estimate these diffusion coefficients for the rubbery, gl ass transition, and glassy regions as a function of polymer concentration a nd application temperature is presented. While the method is empirical in n ature, it is based on carefully executed experimental studies, sound scalin g laws, and agrees extremely well with free volume theories in the rubbery region. The method only requires a knowledge of the pure polymer glass tran sition temperature in order to estimate the diffusivity of molecules like s tyrenic and acrylic monomers (molecular weight of approximately 100 g/mol) at any polymer concentration and for temperatures above and below the polym er glass point. (C) 2001 Elsevier Science Ltd. All rights reserved.