The influence of monomer ionization and hydrolysis on the radical polymerization kinetics of 2-(dimethylamino)ethyl methacrylate in aqueous solution

Abstract

The aqueous solution radical polymerization of 2-(dimethylamino)ethyl methacrylate (DMAEMA) is investigated using in situ nuclear magnetic resonance spectroscopy. While fully ionized DMAEMA is stable over the time scale of polymerization, the non-ionized monomer hydrolyzes at pH > 6.0 to form ionized methacrylic acid (MAA) and 2-(dimethylamino)ethanol, with the hydrolysis rate measured as a function of temperature and pH. Fully ionized DMAEMA polymerizes in water 5 times faster than non-ionized DMAEMA in dimethyl sulfoxide due to the reduced rate coefficient for radical–radical termination. When polymerizations are conducted at pH in the range of 8.0 to 10.1, the reaction is complicated by DMAEMA hydrolysis, with the MAA product copolymerizing to form poly(DMAEMA-co-MAA). Thus, the system requires consideration as a terpolymerization of ionized and non-ionized DMAEMA species with ionized MAA, with the relative rates of polymerization and hydrolysis dependent on reaction temperature, pH, and initiator concentration.