AbstractThe surface IR absorption characteristics of MBS impact modified and unmodified PVC specimens prepared in various ways were determined by ATR‐FTIR techniques. These specimens include compression molded plaques and blow molded bottles. In addition and as a reference point, the IR spectrum of a solution cast film of unmodified PVC was obtained in the transmission mode. The IR spectra in the C‐Cl stretching region for unmodified plaques, i.e. 560 to 750 cm−1, were curve fitted to seven Lorenz functions centered at the literature frequencies, except for one band which was changed from 639 to 636.5 cm−1. Two additional bands (699 and 759 cm−1) were assumed to represent the modifier absorption in modified plaques and bottles. Only peak intensities and band widths were allowed to vary in the curve fitting process. Deconvoluted spectra of selected specimens support the number and location of the absorption peaks.Though these surface spectral changes can be represented in terms of surface configurational partitioning that occurred during processing, a more likely explanation is that conformational changes in the PVC polymer chain has occurred on the surface. Quantities representing the configuration of PVC polymer chains such as non‐syndiotacticity (NSS) or the fraction of PVC backbone carbon atoms that are found in the trans conformation (TRANS) were estimated from Lorenz parameters. NSS and TRANS were found to depend on processing conditions as well as the nature of the modifier.These results are discussed in terms of practical impact tests such as n‐Izod and falling bott