Quaternization kinetics of poly‐4‐vinylpyridine

Abstract

AbstractThe quaternization of poly‐4‐vinylpyridine by n‐butyl bromide in tetramethylene sulfone and in propylene carbonate at 25, 50, and 75°C. begins as a simple second‐order reaction with a rate constant approximately equal to that for 4‐picoline. As the quaternization proceeds, the rate decreases due to the charge which is being built up on the polymer, and the quaternization of the last half of the pyridine side groups occurs at about one‐tenth the initial rate. The kinetics can be summarized by the equation: where x is concentration of bromide ion at time t, A is initial concentration of butyl bromide, B is initial concentration of polymer in monomoles per liter, k0 is the initial rate constant for quaternizing isolated pyridine groups, k2 is the rate constant for quaternizing pyridine groups both of whose neighbors are already quarternized, and α is a parameter which depends on temperature, initial concentrations, and on the intrinsic rate constants. A simple graphical method is described which permits evaluation of k0, k2, and α from the data. At 25° in tetramethylene sulfone, k0 = 5.0 × 10−4 l./mole min., k2 = 5 × 10−5, and α/A = 2 × 10−4.