Side-chain micellization in random copolymers of sodium acrylate and methacrylates substituted with nonionic surfactant moieties: a comparison with sodium 2-(acrylamido)-2-methylpropanesulfonate copolymers

The micelle formation of random copolymers of sodium acrylate (NaAA) and a methacrylate substituted with HO(CH2CH2O)mC12H25 (C12Em) where m=2, 6 or 25 (DEmMA) in 0.1 M NaCl aqueous solutions at pH=10 was investigated in comparison with that of random copolymers of sodium 2-(acrylamido)-2-methylpropanesulfonate (NaAMPS) and DEmMA. Apparent critical micelle concentrations and aggregation numbers of the polymer-bound C12Em moieties in micelles formed from the NaAA-based copolymers of m=2, 6 and 25 were nearly the same as those found for the NaAMPS-based copolymers of m=2, 6 and 25 comparing at the same m. Zero-shear viscosity (η0) increased gradually with increasing polymer concentration (Cp) in a dilute regime, followed by a drastic increase at higher Cp, which is a common feature for both the copolymers. However, the dependence of η0 on m for the NaAA copolymers is completely opposite to that for the NaAMPS copolymers. In a semidilute regime, η0 for the NaAA copolymer of m=2 was ca. 3 and 6 orders of magnitude higher than those of the NaAA copolymers with m=6 and 25, respectively, whereas η0 for the NaAMPS copolymer of m=2 was ca. 1 and 3 orders of magnitude lower than those of the NaAMPS copolymers with m=6 and 25, respectively. At m=2, η0 for the NaAA copolymer is ca. 8 orders of magnitude higher than that for the NaAMPS copolymer. This large difference in the viscosity behavior of the NaAA- and NaAMPS-based copolymers was attributed to a much stronger tendency of the NaAA-based copolymer to undergo interpolymer association when m is small.