Rheological properties of methacrylic acid/ethyl acrylate co-polymer: comparison between an unmodified and hydrophobically modified system

Earlier experimental studies on the emulsion polymerized methacrylic acid/e thyl acrylate co-polymer indicated that the ethyl acrylate (EA) segments ar e sufficiently blocky to induce hydrophobic association between the EA bloc ks once the methacylic acid groups are neutralized by a base. Detailed rheo logical characterization on semi-dilute solutions suggests that the viscoel astic property is caused by the transient network assembled through hydroph obic associations, rather than by physical chain entanglements. In the semi -dilute solution regime, the hydrophobically modified associative polymer e xhibits higher viscosities when compared to the unmodified analogue. This i s due to the formation of higher proportion of intermolecular association b etween the polymer clusters, which enhances the hydrophobic interaction bet ween the hydrophobic macromonomers of different polymer chains. A mechanist ic model is proposed to describe the nature of associations between the blo cky EA and the hydrophobic segments of the polymer. (C) 2000 Elsevier Scien ce Ltd. All rights reserved.