Aggregation Behavior of Copolymer Containing Sulfobetaine Structure in Aqueous Solution

Copolymers containing sulfobetaine (P(AM/DMAPS)) were synthesized by aqueous copolymerization of acrylamide with 3-[N-(2-methacroyloylethyl)-N,N- dimethylammonio]-propane sulfonate. Aggregation and disaggregation of P(AM/ DMAPS) copolymer in aqueous solution as a function of copolymer concentration, added salts, and temperature were studied by dynamic laser light scattering. P(AM/DMAPS) copolymers exist as a mixture of individual chains and interchain aggregation in deionized water. At low copolymer concentrations (below 1.0 g L-1), the intrachain aggregation is dominant. With increasing copolymer concentration, the interchain aggregation is enhanced. The addition of a small amount of salts (CNaCl 0.1 mol L-1; CMgCl2/CaCl2 0.05 mol L-1) leads to the disaggregation of the intra- and interchain aggregation. Further addition of salts results in the enhancement of interchain aggregation. The influence of various cations (Na+, Ca2+, Mg2+) on the aggregation behavior increases in the order Na+ Ca2+ Mg2+. The increase of temperature from 25 degrees C to 60 degrees C facilitates the breakup of intrachain aggregation and the enhancement of interchain aggregation.