Kinetics and Modeling of Radical Copolymerization of Water-Soluble Cationic Monomers
Polyelectrolytes (PELs) are a special class of charged water-soluble polymers utilized in both consumer and industrial applications such as pharmaceuticals, cosmetics, waste-water treatment, flocculating agents, oil drilling and enhanced oil recovery. While their unique solution properties are controlled by the polymer microstructure, studies on the (co)polymerization kinetics are relatively rare due to complexities that arise from polymerization in aqueous phase and electrostatic effects. The knowledge gained from application of specialized experimental techniques such as Pulsed Laser Polymerization (PLP) and in-situ NMR to measure the rate coefficients and study (co)polymerization behavior can aid PEL process and product development efforts. In the present study, cationic monomers, 2-(methacryloyloxyethyl)trimethylammonium chloride (TMAEMC) and 3-(Methacrylamidopropyl)trimethylammonium chloride (MAPTAC) are copolymerized with nonionized (AA) and fully ionized acrylic acid (NaA) in aqueous solution by radical copolymerization to obtain cationic PELs and polyampholytes. The in-situ NMR technique, and in some cases, semi-batch reactor systems, were utilized to obtain the rates of polymerization and monomer composition drifts across the full range of comonomer compositions, for initial monomer weight fraction up to 0.40, and at varying ionic strengths and pHs. Comonomer and copolymer solution properties such as counterion activity, conductivity, pH and viscosity were measured to further understand how the copolymerization kinetics could be affected by reaction conditions. The experimental findings were combined with the rate coefficients measured by our collaborators and implemented into the Predici software to develop of TMAEMC and MAPTAC homopolymerization and their copolymerization with AA and NaA. It is demonstrated that a standard model of copolymerization kinetics can be used to successfully describe rates of monomer conversion, polymer MWs and copolymer compositions for these systems once the influence of the charged monomer on the propagation and termination rate coefficients are accounted for.