Effects of alkyl-chain length on the self-assembly of copolymers of acrylic acid and alkyl acrylate in aqueous media

Effects of the alkyl chain length on the association properties of copolyme rs of acrylic acid (AA) and ethyl (EA), n-butyl (BA) or dodecyl acrylate ID A) were investigated by static light scattering (SLS), rheometry. and foam stability measurements, Apparent weight average molecular weights (Mws) of the copolymers with longer alkyl chains in a phosphate buffer solution of p H 6.8 (BPS) were higher than those having shorter alkyl chains, Aqueous sol utions of AA/DA copolymer exhibited gel-like behavior at polymer concentrat ions higher than 10 wt% whereas solutions of AA/EA and AA/BA copolymers beh aved as a Newtonian fluid even at high concentrations. These observations i ndicate that the AA/DA copolymer forms a three-dimensional network through interpolymer hydrophobic associations. By the addition of the AA/DA copolym er into an aqueous solution of sodium dodecyl sulfate (SDS), the foam stabi lity of the solution was drastically improved, A conclusion from this work is that the dodecyl group is long enough for the AA/alkyl acrylate copolyme rs to undergo significant self-associations as well as associations with su rfactants.