Probing the Concentration Profiles of Additives in Polymers by IR Microspectroscopy: The Diffusion of Cyasorb UV531 in Polypropylene

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Abstract
The recent advancement in FT-IR microspectrometry has provided a convenient way to probe the concentration profiles of additives in polymers. This technique opens up intriguing prospects for investigating additive/polymer or polymer/polymer interaction. In this work, the diffusion of a UV stabilizer, UV531, in polypropylene was selected to illustrate the applications of an IR microscope to monitor the concentration profiles of additives in polymers. In addition, a nonlinear least-squares fitting program was written to obtain diffusion coefficients from concentration profiles based on a theoretical model of the diffusion process. Because IR spectroscopy is functional-group specific, this technique is relatively insensitive to the presence of impurities or other additives in studying additive diffusion in polymers. The sensitivity, the aperturing capability, and the high spatial resolution of FT-IR microprobes make it possible to characterize a wider range of diffusion experiments in a shorter period of time than can be done using traditional techniques.