Luminescence studies of hydrophobically modified, water-soluble polymers. I. Fluorescence anisotropy and spectroscopic investigations of the conformational behaviour of copolymers of acrylic acid and styrene or methyl methacrylate

Abstract

Fluorescence spectroscopy and anisotropy measurements have been used to study a series of styrene – acrylic acid, STY–AA, and methyl methacrylate – acrylic acid, MMA–AA, copolymers in dilute methanolic and aqueous solutions. Copolymerization of either STY or MMA with AA has little effect upon the rate of intramolecular segmental motion in methanol solutions. In aqueous media, intramolecular hydrophobic aggregation occurs and restricts the macromolecular dynamics to an extent dependent upon pH, nature of the comonomer, and copolymer composition. The hydrophobic domains formed in these copolymer systems can solubilize organic guests. In this respect, STY is a more powerful modifier of AA-based polymer behaviours than is MMA. In general, the hydrophobic modification increases the solubilization power of the resultant polymer. Furthermore, the copolymers retain their solubilization capacities to higher values of pH the more hydrophobic the comonomer and the greater its content in the copolymer. The interiors of the hydrophobic aggregates reduce the mobilities of occluded guests: the microviscosities of the domain interiors depend upon the nature of the hydrophobe, pH, and copolymer composition. Keywords: fluorescence, anisotropy, water-soluble polymers, acrylic acid, hydrophobic modification.