The nucleophilic substitution reaction of poly(vinyl chloride) (PVC) with potassium 4-acetamidothiophenolate was performed in a cyclohexanone solution. The quantitative microstructural analysis, as a function of the conversion, was followed by C-13 NMR spectroscopy. Through a comparison of the microstructural changes with the degree of substitution, a small fraction of mmr tetrads was found to react occasionally with the central chlorine of the mr triad instead of the mm, such as for sodium benzenethiolate (NaBT). This conclusion was confirmed by Fourier transform infrared results. However, unlike NaBT, the evolution of the glass-transition temperature (T-g) with the degree of conversion changed with the degree of substitution similarly to the ratio of the extents to which mmr and rrmr structures intervened in the substitution reaction. From these studies, it followed that the specific interactions due to the polar nature of the nucleophile enhanced the molecular-microstructure-based mechanisms, which were responsible for T-g. Such a novel quantitative correlation, compared with more tentative ones obtained previously, presents valuable insight into the role of the stereochemical microstructure in the glass-transition process in PVC. (C) 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 1857-1867, 2004