Aqueous solution properties of hydrophobically associating copolymers

Abstract

Water-soluble polymers containing a small amount of hydrophobic groups have been prepared in aqueous medium by radical copolymerization of acrylamide and ethylphenylacrylamide as the hydrophobic comonomer. Two methods of synthesis h ave been used: a “micellar” process in which the use of a surfactant ensures the solubilization of the water insoluble monomer, and a “heterogeneous” process wherein the insoluble monomer is simply dispersed in water. The copolymer compositions have been determined by UV spectrophotometry and the molecular weights by light scaattering. The effect of sample preparation on the rheological behavior is discussed. The more pronounced thickening effect observed for copolymers compared to homopolyacrylamide results from intermolecular hydrophobic associations. Under shear, associations are disrupted and a strong but reversible shear-thinning effect is observed. This dissociation process is relatively slow, as indicated by the thixotropic behavior at high-shear rates. On the contrary, a rheopexic behavior can be observed at low-shear rates.