FTIR imaging of polymer dissolution. 2. Solvent/nonsolvent mixtures

transform infrared (FTIR) spectroscopic imaging employing focal plane array (FPA) detection is used to study the dissolution of poly(alpha -methylstyr ene) (PAMS) by solvent solutions containing systematically varied amounts o f a nonsolvent. Sequential images were acquired as dissolution proceeded an d the samples were not disturbed during image acquisition. Qualitative spat ial and chemical distribution of each species within the field of view was obtained by analyzing images based on the characteristic vibrational modes of each species, while quantitative information was gathered through the ca lculation of individual concentration profiles along the chemical gradient. The images and absorbance profiles showed selective solvent penetration in all cases. In general, the dissolution rate of the polymer decreased linea rly with the weight-percent of nonsolvent present in the solution. Anomalou sly high dissolution rates were observed for solutions containing similar t o5-10% nonsolvent. This increase was attributed to the formation of a band of high polymer concentration perpendicular to solvent diffusion direction during the dissolution process. The efficacy of FTIR imaging in studying th e spatiotemporal variation of microscopic gradient evolution in multicompon ent systems is underscored.