Aggregation behavior of methacrylic acid/ethyl acrylate copolymer in dilute solutions

A co-polymer consisting of methacrylic acid (MAA) and ethyl acrylate (EA) is commonly used as the polymer backbone for a class of hydrophobically modified alkaline soluble emulsion (HASE) polymer. At alkaline pH, the emulsion particle solubilizes, yielding a molecular structure that is currently not well understood. The chain conformation of a model MAA/EA copolymer (designated as HASE107) in 0.1 M NaCl at pH of 9 was studied by dynamic and static light scattering techniques. In dilute solutions, two decay modes in the distribution function are observed. These two modes (referred to as the fast and slow modes) are attributed to the translational diffusion of the unimers and the aggregates. In order to isolate the aggregates, the HASE107 polymer was dissolved in a moderately good solvent (tetrahydrofuran was chosen), where only a single diffusion mode is observed. The results confirmed that the co-polymers synthesized via emulsion polymerization technique are blocky, and in aqueous solutions, the blocky and more hydrophobic EA segments associate to form aggregates consisting of a few polymer chains.