| Abstract: | Quaternization reactions of poly(vinylpyridines) with alkyl halides show retardation in excess of that predicted by the classical second-order kinetics. Based on the classical collision and transition state theories, a kinetic model has been developed to quantify such retardation, in which the overall reaction rate is characterized by a rate constant k0 of the intrinsic reactivity between a pyridyl group and an alkyl halide group, and by a steric hindrance effect parameter α. The latter accounts for the degree to which the rate of collisions of reactants is reduced, or to which the freedom of movement of the reactants in the transition state is restricted as the reaction proceeds. The resulting kinetic expression has been validated using experimental results reported in the literature and those of our own. The functional dependence of k0 and α values on the nature of poly(vinylpyridines) and that of alkyl halides is explained. Other factors affecting k0 and α, including changes in macromolecular dimensions and/or in the distribution of residue environment, quality of solvent, and reaction temperature, are discussed. © 1993 John Wiley & Sons, Inc. |
