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

1999; American Chemical Society; Volume: 32; Issue: 14 Linguagem: Inglês

10.1021/ma990202j

1520-5835

Tetsuya Noda, Yotaro Morishima,

Advanced Polymer Synthesis and Characterization

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 increasing polymer concentration, whereas Nagg remains constant at about 158 independent of the polymer concentration. On the basis of the results from the fluorescence and QELS measurements, a unicore micelle model was proposed for the copolymer with fDMA = 9 mol %, and a bridged micelle model was proposed for the copolymer with fDMA = 15 mol %.