INFLUENCE OF THE HYDROPHOBE STRUCTURE ON COMPOSITION, MICROSTRUCTURE,AND RHEOLOGY IN ASSOCIATING POLYACRYLAMIDES PREPARED BY MICELLAR COPOLYMERIZATION

Acrylamide polymers modified with low amounts of alkyl- or alkylarylac rylamides (1-5 mol %) have been prepared by an aqueous micellar copoly merization technique. This method is known to lead to multiblock copol ymers in which the number and length of the hydrophobic blocks vary wi th the initial number of hydrophobes per micelle. The incorporation be havior of different types of hydrophobes and their effects on the rheo logical copolymer properties have been investigated. Interestingly, th e use of disubstituted acrylamides leads to an average copolymer compo sition independent of the degree of conversion, in contrast to what is observed with monosubstituted acrylamides. Solubility measurements of both types of hydrophobes indicate that the micellar dynamics is not responsible for this behavior, but rather the difference in polarity b etween the bulk phase and the micellar phase. This microenvironment ef fect modifies the reactivity ratios of those hydrophobes capable of fo rming hydrogen bonds, whereas the reactivity of the other hydrophobes remains unaffected. The rheological properties of the samples are disc ussed in terms of copolymer microstructure and type of hydrophobe used (bulkiness, degree of branching, and alkyl chain length). For example , at similar hydrophobe levels, double-chain hydrophobes considerably enhance the thickening efficiency with respect to single-chain hydroph obes.