Techniques for chloromethylation of polyarylether sulfones, poly-phenylene oxide, phenolic resin, and a model compound for the polyarylether sulfone are described. The rates of quaternization of chloromethylated polyarylether sulfone, I, and the corresponding model compound, II, with triethylamine, tri-n-butylamine, and quinuclidine in either DMSO or DMSO/dioxane are reported. Second-order kinetics are observed in the quaternization of II for the entire range of substitution. In contrast, quaternization of I followed second-order kinetics during the initial 35–60% of reaction only; higher degrees of quarternization occurred at reduced rates. After evaluating the potential impact of steric hindrance, added electrolyte, and initial extent of chloromethylation, the decrease in quaternization rate at high degrees of substitution is attributed to steric effects imposed by restricted rotation of the polymer chain. Comparable retardations are not observed during the quaternization of chloromethylated polystyrene under identical conditions.