Analysis of butyl acrylate diffusion in a glassy polystyrene matrix to predict gradient structure

To be able to control composition structure in gradient polymers prepared b y sequential polymerization, diffusion phenomena has to be considered, part icularly for the first 100% weight increment in a glassy polymer matrix. Wi th that purpose, an analytical model to predict diffusion in that region ha s been developed for amorphous polymers. The inclusion of a relaxation time to estimate surface concentration changes during sorption led to diffusion coefficients one order of magnitude higher than Fickian coefficients. Howe ver, adding a volume increment term to account for polymer swelling, diffus ion coefficients went up to 48 rimes the Fickian values. Experimentally, bu tyl acrylate with a small amount of photosensitizer was diffused into a sli ghtly crosslinked polystyrene slab matrix at different temperatures in the glassy region. After fixing the gradient composition by photopolymerization , chemical structures throughout the slab were determined by FTIR. The prop osed model was confronted with experimental sorption showing a close fit at the different temperatures in the region of interest. (C) 2001 John Wiley & Sons, Inc.