Light scattering of dilute hydrophobically modified alkali-soluble emulsion solutions: Effects of hydrophobicity and spacer length of macromonomer

A novel comb water-soluble associative polymer (hydrophobically modified al kali-soluble emulsion (HASE)), comprising of a random copolymer of methacry lic acid (MAA), ethyl acrylate (EA), and 1 mol % of hydrophobically modifie d macromonomers, was studied using laser light scattering and rheological t echniques. The hydrophobic substituents are separated from the backbone by a poly(ethylene glycol) (PEG or PEG) spacer chain. The hydrophobicity of th e hydrophobic substituents and the length of PEO spacers control the micros tructure of the aggregates or clusters. In dilute solution regime, the rela xation times of both unimers and aggregates are almost independent of hydro phobic groups and PEO spacer length. The aggregates are formed via the clos ed-association mechanism, and the balance of electrostatic and hydrophobic interactions controls their microstructures. However, by varying the hydrop hobicity and the length of the PEO spacer chains, the internal conformation of the aggregates changes. Results from static and dynamic light scatterin g are consistent with the trends observed from rheological measurements.