Chain association, alkylacrylamide copolymers

To elucidate the mechanism of chain association, we prepared three series of N-alkylacrylamide-acrylamide copolymers containing up to 0.75 mol % of Cg, Cio, and C12 N-alkylacrylamide monomers. The copolymerizations were conducted with potassium persulfate as the initiator in an aqueous medium containing a high concentration of sodium dodecyl sulfate surfactant (28). The reaction parameters and solubility of the resulting copolymers are given in Table I. Table I indicates solubility in water of all... 

The rates of solubilization, however, and the apparent homogeneity of the solutions deserve comment. First, the extent of incorporation of the N-alkylacrylamide in the copolymer is not determinable from elemental analysis or NMR measurements because of the low concentration in the feed initially. Second, solubilization of purified, freeze-dried samples is often difficult because of inter- and intramolecular associations. Finally, even under dilute conditions, a time dependence on dissolution is observed with some solutions, which require weeks to reach constant values of apparent viscosity. Optical cloudiness with stringy texture is often observed with the longer alkyl chains at higher concentration. 

Hydrophobically associating acrylamide based polymers were explored as a means of alleviating the salt sensitivity observed in the block systems. A micellar polymerization technique was developed to enable preparation of random copolymers of acrylamide and N-n-alkylacrylamide. When these copolymers were dissolved in an aqueous solvent, the hydrophobic groups associated to minimize their exposure to water. The hydrophobic associations provided an additional dimension to polymer molecular weight and chain expansion by ionic groups for the control of aqueous fluid rheology. 

In Figure 5 apparent viscosity is plotted versus polymer concentration for copolymers of 0.75 mole % octyl and decyl-acrylamide and 0.25 mole % dodecylacrylamide. Copolymers of acrylamide with decylacrylamide and octylacrylamide exhibit a greater dependence of the viscosity on concentration than copolymers with dodecylacrylamide at the aforementioned compositions. These results indicate that the interchain associations increase not only with increasing content of an N-alkylacrylamide but also with the length, or hydrophobicity of the side chain. 

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