Acrylamide polymers modified with low amounts of alkyl- or alkylarylacrylamides (1−5 mol %) have been prepared by an aqueous micellar copolymerization technique. This method is known to lead to multiblock copolymers in which the number and length of the hydrophobic blocks vary with the initial number of hydrophobes per micelle. The incorporation behavior of different types of hydrophobes and their effects on the rheological copolymer properties have been investigated. Interestingly, the use of disubstituted acrylamides leads to an average copolymer composition 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 between the bulk phase and the micellar phase. This microenvironment effect modifies the reactivity ratios of those hydrophobes capable of forming hydrogen bonds, whereas the reactivity of the other hydrophobes remains unaffected. The rheological properties of the samples are discussed 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 hydrophobes.

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Compositionally homogeneous modified polyacrylamides were synthesized by micellar copolymerization leading to hydrophobically associating polymers with a large range of viscosifying properties. The strength of the hydrophobic associations depends on the structure of the hydrophobic comonomer and its distribution. Hydrophobic comonomers with a bulky structure lead to particularly strong thickening properties. Contrary to polyacrylamides that present a classical high affinity adsorption isotherm on alumino silicate surface, the adsorption of hydrophobically modified polymers increases with polymer concentration. The effect is observed even if no intermocular associations are evidenced in solution. The bound fraction of water was determined by 1H NMR, thus giving indirect information on the adsorbed layer structure. Some modified polymers nearly completely replace the bound water, forming a quasi impenetrable adsorbed layer.

A micellar polymerization process has been used to prepare polyacrylamide or poly(acrylic acid) hydrophobically modified with low amounts (1–5 mol%) of an N‐alkyl‐ or N‐alkylarylacrylamide. The effect of the initial monomer segregation on the copolymer microstructure and the copolymerization mechanism has been investigated. This method leads generally to multiblock copolymers in which the number and length of the hydrophobic blocks vary with the initial number of hydrophobes per micelle. Interestingly, the copolymerization of acrylamide with disubstituted acrylamides leads to homogeneous samples with an average copolymer composition independent of the degree of conversion, in contrast to what is observed with monosubstituted acrylamides for which a drift in composition is observed. The difference in polarity between the bulk phase and the micellar phase is responsible for this behavior. This microenvironment effect modifies the reactivity ratios of those hydrophobes capable of forming hydrogen bonds, whereas the reactivity of the other hydrophobes remains unaffected.