Polymer association. IV. Hydrogen bonding and melt viscosities in copolymers of styrene with methacrylic acid

Melt viscosities of styrene homopolymers and copolymers with 1.5 to 23 mole‐% methacrylic acid were measured with a parallel plate plastometer. Apparent viscosities were found to drop off sharply with increasing rate of shear in the range 10−4 to 10−1 sec.−1. An increasing concentration of carboxyl groups led to a pronounced increase in the melt viscosity and the activation energy for viscous flow. Infrared spectra of the copolymers were recorded while the samples were subjected to various thermal cycles. Equilibrium in the dimerization of carboxyl groups was established very rapidly above about 100°C., but the equilibrium was effectively frozen at lower temperatures. Samples as originally prepared by precipitation from dilute solution were further removed from equilibrium than samples quenched from high temperatures. The results are discussed in terms of the rate process theory of viscosity.