STRUCTURE AND FLOW BEHAVIOR OF CROSS-LINKED ETHYL ACRYLATE-METHACRYLIC ACID COPOLYMER DISPERSION PARTICLES

Changes in viscosity, pH and static light scattering behavior on alkal i addition of model dispersions of statistical copolymers of ethyl acr ylate: with 15 and 50 wt% of methacrylic acid prepared by semicontinuo us emuslion copolymerization and crosslinked with various amount of N, N'-methylenebisacrylamide were investigated. It was found that about 1 % of crosslinking agent was sufficient to prevent unpredictable disint egration of dispersion particles and gauranteed reproducible flow beha vior of alkalinized dispersions. The viscosity of alkalinized dispersi ons of crosslinked particles at low concentration is controlled by the effective hydrodynamic volume of swelled particles which decreases wi th the crosslinking degree of copolymer. On the other hand, at higher particle concentration close to critical concentration at which the sp ace is filled up by swelled particles the influence of particle intera ction prevails and due to lower deformability of crosslinked particles viscosity increases with a crosslinking degree. In comparison with si milar dispersions prepared without a crosslinking agent these results indicated much uniform structure of dispersion particles and suppressi on of influence of random crosslinking due to chain transfer reactions . The study shows that dispersions of crosslinked copolymers of this t ype could be considered as thickners of latex binders with stable and reproducible thickening properties.