ASSOCIATING BEHAVIOR OF POLYACRYLAMIDES HYDROPHOBICALLY-MODIFIED WITHDIHEXYLACRYLAMIDE

Polyacrylamides hydrophobically modified with a small amount of dihexy lacrylamide (HMPAM) have been prepared by means of an aqueous micellar polymerization technique. This process leads to copolymers in which t he hydrophobic molecules are randomly distributed as blocks in the acr ylamide backbone. Keeping constant the hydrophobe level (1 mol%), the length of the blocks was adjusted by varying the surfactant content us ed in the synthesis, i.e. by varying the number of hydrophobes per mic elle, N-H The resulting copolymers are homogeneous in composition, but have a different microstructure (blockiness). The rheological propert ies of the samples in aqueous solution have been investigated as a fun ction of polymer concentration, polymer conversion, temperature and in the presence of surfactant, using steady flow and oscillatory experim ents. The hydrophobic modification of the polyacrylamide backbone indu ces a slowing down of the reptation movement of the polymer chains. Th e results stress the major role of the hydrophobe distribution in the copolymer for a good control of the thickening efficiency of associati ng HMPAM. (C) 1997 Elsevier Science Ltd. All rights reserved.