EFFECTS OF WATER-SOLUBLE SPACERS ON THE HYDROPHOBIC ASSOCIATION OF FLUOROCARBON-MODIFIED POLY(ACRYLAMIDE)

A number of acrylamide-acrylate copolymers were synthesized in which the acrylate (CH2=CHCOO(CH2CH2O)(n)R) is hydrophobic on account of the presence of a 1,1-dihydroperfluorooctyl group or a dodecyl group connected to the acrylate via a -(CH2CH2O)(n) hydrophilic spacer (n = 0-3). Copolymerization of these monomers was initiated by sodium metabisulfite and ammonium persulfate at 60 degrees C in aqueous media in the presence of surfactants and acetone. The low shear viscosities of 0.5 wt % solutions of these copolymers as a function of comonomer molar content gave bell-shaped curves having maxima at 0.10-0.60 mol% comonomer, consistent with competitive inter- and intramolecular hydrophobic association. The copolymers having perfluorocarbon pendent groups gave higher viscosities at lower comonomer content. Furthermore, for both the hydrocarbon- and perfluorocarbon-containing copolymers the viscosities increased, and the comonomer content at the viscosity maximum decreased, with increasing spacer length. The increased effectiveness of the longer spacers is attributed to entropy effects in the formation of polymer assemblies.