Synthesis, characterization, and testing of acrylamide-based polymers
Date
1997
Authors
Klimchuk, Keith Adrian
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Abstract
In relation to polyacrylamide, copolymers of acrylamide with N,N-dimethylacrylamide, methacrylamide, and N-t-butylacrylamide were prepared to study the effect of steric bulk and its degree and proximity to the polymer back-bone on synthesis to high conversions and molecular weights, polymer chain extension, solution behaviour, and flocculant ability. Cationic derivatives of copolymers containing a low proportion of the substituted acrylamide component were also prepared to study the effect of charged groups in relation to steric bulk on polymer chain extension and flocculant ability.
All copolymers were characterized by photoacoustic FTIR, 13C NMR, and viscometry. Elemental analysis was used to determine the compositions of the copolymers ofN,N-dimethylacrylamide and methacrylamide with acrylamide. The percentage cationicity was determined for the cationic derivatives.
For equivalent experimental conditions, only the copolymers of N,N-dimethylacrylamide with acrylarnide gave similar conversions and higher molecular weights than polyacrylamide. Copolymerization ofN-t-butylacrylamide with acrylarnide was made possible by using a 1: 1, t-butanol / distilled water solvent. However, only the copolymers containing less than 60 mot% of N-t-butylacrylamide were water soluble.
Multi-angle laser light scattering in the batch mode was used to determine polymer chain extensions in solvents adjusted to various pH levels and solvents adjusted to a constant pH but varied in electrolyte concentration. Polymer chain extensions greater than those of polyacrylamide were measured only for the copolymers of N,N-dimethylacrylamide with acrylamide. Solution confonnations of all the copolymers and polyacrylamide were resistant to variations in pH, but only the copolymers were resistant to changes in electrolyte concentration at constant pH. The solution conformations of the commercial flocculants Percol 721 (cationic polyacrylamide ), Percol E-24 (anionic polyacrylamide), and Percol 351 (nonionic polyacrylamide) were all affected by changes in electrolyte concentration at constant pH.
Viscornetric analysis of the cationic derivatives of the nonionic copolymers containing the lowest proportion of the substituted acrylamide component showed a greater contribution to polymer chain extension from charged groups than from steric bulk.
All the copolymers functioned as tlocculants for a 1 % Na-kaolinite test medium at near neutral pH and containing 1.138 x 10-4 M NaCl, but only the copolymers of N,N-dimethylacrylamide with acrylamide performed better than polyacrylamide as flocculants. Also, the flocculation performance of the copolymers with a low proportion of N,N-dimethylacrylamide was comparable to the performance of commercial flocculants. The flocculation performance of the cationic derivatives was poorer than the performance of their nonionic precursors.
It was concluded from the results of the polymerization, solution behaviour, and flocculation experiments that copolymers of acrylamide with N,N-dimethylacrylamide can give improved polymer chain extension and flocculation perfonnance in the presence or absence of electrolyte, as compared to polyacrylamide. In addition, copolymerization of N,N-dimethylacrylamide with acrylamide to give molecular weights greater than 5 x 106 g/mol and conversions greater than 70 %, as well as the conversion of the nonionic copolymer precursor to a cationic derivative containing 26 mol % cationicity, could offer useful starting points for commercial use.