Hydrophobically associating polyacrylamides and their partially hydrolyzed derivatives prepared by post-modification. 1. Synthesis and characterization

Hydrophobically associating polyacrylamides (HAPAMs) or hydrophobically associating hydrolyzed polyacrylamides (HHAPAMs) are generally prepared by micellar copolymerization which leads to a blocky distribution of hydrophobes and drifted compositions. In the present study, a series of HAPAMs were prepared by direct N-alkylation of the amide groups of a parent polyacrylamide (PAM) in DMSO with alkyl bromide in the presence of potassium tert-butoxide. The derivatives HHAPAMs with various charge densities were obtained by partial hydrolysis of HAPAM precursors with 0.25 M NaOH in a 0.1 M NaCl aqueous solution at 50 °C. Molecular weight determination showed no degradation occurred in both processes. 1H and 13C solution NMR elucidations of hydrophobic group incorporation and degree of hydrolysis showed good agreements with feed ratio. Statistical hydrophobic group distribution along the polymer backbone was expected. For samples with high viscosity and poor solubility, gel HRMAS NMR was successfully employed. The results indicate that post-modification is a more effective way to control the composition of HAPAMs compared against micellar process.