Hydrophobic Association of Random Copolymers of Sodium 2-(Acrylamido)-2-methylpropanesulfonate and Dodecyl Methacrylate in Water As Studied by Fluorescence and Dynamic Light Scattering

Abstract

The association behavior of random copolymers of sodium 2-(acrylamido)-2-methylpropanesulfonate (AMPS) and dodecyl methacrylate (DMA) with its content (fDMA) varying from 1 to 15 mol % was investigated by fluorescence and quasielastic light scattering (QELS) techniques in 0.1 M NaCl aqueous solutions. The association behavior of the copolymers was found to depend strongly on fDMA. When fDMA < 3 mol %, some polymer chains exist as unimers with a hydrodynamic radius (Rh) of about 5 nm while some polymers form multipolymer aggregates with Rh ≈ 100 nm, arising from “hydrophobic cross-linking” by the interpolymer association of dodecyl groups. When fDMA is increased to 9 mol %, interpolymer hydrophobe associations lead to the formation of a multipolymer micelle with Rh ≈ 10−13 nm. The aggregation number (Nagg) of dodecyl groups in a micelle core was estimated to be about 195. When fDMA is further increased to 15 mol %, Rh for the multipolymer micelle markedly increases to 70−180 nm, the size increasing with in...