Stimuli Responsive Self-Assembly of 3-(Octyloxy)-3-Oxopropyl Acrylate-Co-Acrylic Acid Polymer in Aqueous Media

A novel copolymer based on 3-(alkyloxy)-3-oxopropyl acrylate and acrylic acid was synthesized and characterized. Surface tension and fluorescence probe techniques (using N-phenyl-1-naphthylamine as a probe) were employed to evaluate the surface properties of the amphiphilic copolymer. The copolymer was found to reduce the surface tension of water to 40–46 mN/m depending on the pH of the medium. The critical aggregation concentration of the copolymer determined by surface tension measurements was found to be 0.28 mg/ml at pH 4, 1.13 mg/ml at pH 8, and 1.44 mg/ml at pH 10, very close to those obtained by steady state fluorescence probe techniques (0.21, 1.13 and 1.48 mg/ml, respectively, at pH 4, 8, and 10). The pH-induced structural transitions of the copolymer were also studied using steady state fluorescence with pyrene and 1,6-diphenyl-1,3,5-hexatriene as probes, dynamic light scattering and transmission electron microscopy. The protonation of pendant carboxylate groups at acidic pH makes the aggregate compact and rigid. Conversely, ionization of the carboxylate groups under alkaline conditions resulted in larger aggregates.