A series of random copolymers of sodium acrylate and oligo(ethylene oxide) alkyl ether methacrylates (CnEmMA) with different lengths of ethylene oxide (EO) and alkyl groups were prepared by free-radical copolymerization at varying copolymer compositions. The lengths of the EO units (the number of EO units) (m) and the numbers of carbon atoms in the alkyl groups (n) ranged from 0 to 8.7 and 1 to 6, respectively. The copolymers with n = 1 and m = 1−8.7 exhibited a marked increase in solution viscosity at polymer concentrations (Cp) higher than their overlap concentrations (C*) when the CnEmMA contents (x) in the copolymers were in a certain limited range. Namely, there was an optimum x value that yielded the highest viscosity as a consequence of the competition between inter- and intrapolymer associations; the maximum viscosities occurred around x ≈ 25, 15, 10, 7, and 3 mol % for m = 1, 2, 3, 4.2, and 8.7, respectively. The maximum viscosity decreased significantly as n was increased on going from 1 to 6, a...