J. Hernandez-Barajas and D. Hunkeler: Copolymers of Acrylamide and Quaternary Ammonium Cationic Monomers 723 z Copolymers of Acrylamide and Quaternary Ammonium Cationic Monomers: Characterization by zyxwv HPLC and Copolymer Composition Control Jose Hernandez-Barajas and David Hunkeler Department of Chemical Engineering, Vanderbilt University, Nashville, TN 37235, USA zyxw Key Words: Acrylamide zyxwvutsr / HPLC / Polymers / Quaternary Ammonium Monomers / Semi-batch Polymerization Copolymers of acrylamide with quaternary ammonium cationic monomers (dimethylaminoethylacrylate-methyl chloride, DMAEA and dimethylaminoethylmethacrylate-methyl chloride, DMAEM) have been synthesized by in- verse-emulsion copolymerization using both sorbitan monoleate (SMO) and a block copolymeric surfactant (HB246) whose hydrophilic moiety is polyethylene oxide and whose hydrophobic moiety is poly-12 hydroxy stearic acid. Residual monomer concentrations were determined by means of an optimized HPLC method using a CN coated column. The optimized conditions consist of an acetonitrile-water mobile phase with a ratio of zyx 50: 50 vol% with dibutylamine used as an additive to reduce the adsorption of the cationic monomer at a concen- tration of 0.01 M and phosphoric acid to adjust the pH. The results indicate that the choice of surfactant in- fluences strongly the quality of the copolymers produced. For example, more uniform copolymers of acrylamide and DMAEA can be synthesized using the block copolymeric surfactant (HB246) at faster production rates in comparison with sorbitan monoleate (SMO). However, a composition drift is observed in the inverse-emulsion copolymerization of acrylamide and DMAEM using HB246. It is shown that uniform water soluble copolymers of acrylamide and DMAEM can be produced by implementing semi-batch policies with non time-varying feed- rates. 1. Introduction Over the past two decades the consumption of cationic water soluble polymers has increased rapidly [l]. Cationic homopolymers and copolymers with acrylamide are now applied for fines retention in paper making, as flocculants and biocides in water treatment, as stabilizers for emulsion polymerization, in cosmetics and pharmaceuticals, and in general wherever aqueous solid-liquid separations are re- quired. Cationic polymers can be categorized by the chemical na- ture of the charged substituent. Ammoniums (primary, se- condary, tertiary and quaternary) have had the most signifi- cant commercial impact since they can be synthesized to a variety of chain architectures and sizes. By comparison, polyphosphoniums are limited to oligomeric molecular weights [2 - 51 and sulphonium monomers are generally unstable and less readily available than quaternary am- monium compounds [6, 71. Polydiallyldimethylammonium chloride (PDADMAC) was the first synthetic flocculant approved for potable water clarification by the United States Public Health Ser- vice [8] and has historically been the most widely produced polyelectrolyte. Other commercially important cationic polymers are derived from dimethylaminoethyl methacry- late-methyl chloride (DMAEM), first synthesized by Win- berg in 1956 and dimethylaminoethyl acrylate-methyl chloride (DMAEA). These cationic monomers are often co- polymerized with acrylamide to produce supermolecular polyelectrolyte structures. The resulting flocculants are nontoxic and more efficient than either of the respective nonionic and cationic homopolymers [9]. They also offer advantages over inorganic flocculants such as alum, includ- ing smaller dosage requirements, less floc generation and a reduction of the ash produced during incineration. Most of the cationic water soluble polymers are produced by heterophase water-in-oil (inverse-emulsion) polymeriza- tions. This process involves the dispersion of an aqueous monomer(s) solution in an aliphatic continuous phase. Nonionic steric emulsifiers are blended to achieve an overall HLB (Hydrophilic-Lipophilic Balance) of between 4 and 9 in order to prevent particle coalescence. The polymeriza- tions take place in batch reactors under inert atmospheres using chemical initiators. Temperatures in the range be- tween 25 - 55 "C are employed with continuous vigorous agitation. Often temperature profiles which increase with conversion are utilized. The level of understanding of inverse-emulsion polymer- ization has continued to grow over the last 20 years. During the 1980s, significant efforts were dedicated toward the mechanism, kinetics and modeling of the inverse-emulsion homo- and copolymerization processes. The first general mechanism for any type of inverse-macroemulsion poly- merization was proposed in 1987 by Hunkeler et al. [ 101 and subsequently expanded and developed into a kinetic model for homopolymers of acrylamide [I 11 and copolymers of acrylamide and quaternary ammonium cationic monomers [12]. However, for the case of copolymers, these kinetic models are limited by the availability of good values of reactivity ratios for the monomers involved. Moreover, since the reactivity ratios are complex functions of mono- mer concentration, pH, the ionic strength of the reaction mixture and the extent of the reaction, the kinetic modeling of the inverse-emulsion copolymerization of acrylamide based polymers becomes difficult. Additionally, the studies of the inverse-emulsion copolymerization of cationic water soluble polymers have been limited to the use of sorbitan esters of fatty acids as stabilizers, with the use of semi-batch inverse-emulsion copolymerization processes to produce uniform copolymers confined to the patent literature. This paper reports: i) an optimization of a HPLC method for the separation of mixtures of acrylamide and quater- nary ammonium cationic monomers, ii) a comparison of Ber. Bunsenges. Phys. Chem. 100, 723 - 729 (1996) No. 6 zyxwvuts 0 VCH Verlagsgesellschaft mbH, 0-69451 Weinheim, 1996 0005-9021/96/0606-0723 $15.00+.25/0