The nucleophilic substitution reactions on poly(vinyl chloride) (PVC) with potassium 4-acetamidothiophenolate, potassium 2-naphthalenethiolate, and sodium 2-mercaptobenzothiazolate have been undertaken in a cyclohexanone solution. The aim was to study, from a comparative point of view, the influence of nucleophile characteristics, in particular bulkiness, reactivity, and nucleophile polarity, on the reaction mechanisms by following the microstructural evolution with the degree of substitution of the same PVC sample with three types of nucleophile under the same experimental conditions. The quantitative microstructural analysis as a function of conversion has been followed by C-13 NMR spectroscopy. Because of the steric hindrance and moderate reactivity of 2-mercaptobenzothiazolate, the stereoselective nature of the reaction is enhanced, occurring via the meso-racemic (mr) triad of mmr tetrad, inoperative in practice, unlike the other nucleophiles. This circumstance and the fact that the bulkiness of the nucleophile and interacting effects provide an enhancement of the molecular microstructure-based mechanisms, such that glass-transition temperature (T-g) varies with the degree of substitution, in all cases, along with the ratio between the extent to which mmr and rrmr structure intervene in the substitution reaction, thereby providing new and valuable information regarding the T-g-microstructure relationship. (C) 2004 Wiley Periodicals, Inc.