Microstructure of dilute hydrophobically modified alkali soluble emulsion in aqueous salt solution

The microstructure of a model HASE associative polymer in aqueous salt solu tion is complex and has not been defined until now. On the basis of the res ults from static and dynamic light scattering studies, a physical model des cribing the microstructure of a model HASE polymer in aqueous salt solution is proposed. The model HASE polymer contains a copolymer backbone of equal moles of methacrylic acid (MAA) and ethyl acrylate (EA) with 1 mol % of C1 6H33 hydrophobic modified macromonomer distributed randomly along the backb one. In very dilute aqueous solutions (0.005-0.1 wt %), two decay modes are observed in the relaxation time distribution function. The fast and the sl ow modes correspond to the translational diffusion of the unimers and the p olymer aggregates (consisting of about five polymer chains), respectively. The polymer aggregate is formed by association of the hydrophobic macromono mer via a closed association mechanism. When the polymer concentration incr eases, the polymer aggregates grow in size. The fractal dimension, d(f), de creases with increasing polymer concentrations, indicating that the aggrega tes are becoming less compact. At the same time, when the polymer concentra tion exceeds 0.1 wt %, the unimers are transformed to oligomers consisting of two or more polymer chains.