ATR/FT-IR and Raman microscopic investigation of diffusion and distribution of silane coupling agents in PVC films

We have combined attenuated total reflectance/Fourier transform infrared (A RT/FT-IR) and Raman microscopy to examine the diffusion rates and redistrib ution profiles of three different silane adhesion coupling agents into plas ticized and unplasticized PVC. Below the glass transition temperature (T-g) of the polymer, little or no diffusion occurs, and above the T-g (for pure PVC at about 70 degrees C) the three silanes behave differently, reflectin g their different propensities to hydrolysis and subsequent condensation. F or plasticized PVC, the fitted diffusion coefficients (obtained via the dua l mode model) increase rapidly with increasing (adipate) plasticizer conten t and decreasing T-g. Correlation of this behavior is with chain "mobility" and not with silane size nor shape. The infrared data for unplasticized PV C Laminates were confirmed by using Raman microscopy. Redistribution within the polymer film is shown to be induced hv heating to 70 degrees C. Howeve r, the Raman data give a more accurate picture of the silane distribution t hroughout the film. Although no direct adhesion mechanistic information has been obtained, it has been shown that there are detailed differences in si lane diffusion behavior which must be associated with reactivity difference s, both within the polymer and at the Si/SiO2/SiOH interface.