Free-Radical Polymerization Kinetics of 2-Acrylamido-2-methylpropanesulfonic Acid in Aqueous Solution

Abstract

The SP−PLP−NIR technique, which combines pulsed laser polymerization (PLP) initiated by a single pulse (SP) with time-resolved monitoring of the resulting monomer conversion via near-infrared (NIR) spectroscopy, was used to investigate the kinetics in aqueous solution of 2-acrylamido-2-methylpropanesulfonic acid (AMPS). For initial AMPS concentrations of 2.79 mol·L-1 (50 wt % AMPS) and 1.04 mol·L-1 (20 wt % AMPS), the ratio of (chain length averaged) termination and propagation rate coefficients, 〈kt〉/kp, was measured up to almost complete monomer conversion at temperatures between 10 and 40 °C and ambient pressure. Up to 80% monomer conversion, 〈kt〉/kp is only slightly lowered, whereas there is a clear decrease upon further increasing conversion. Variation of temperature and of pH does not significantly affect 〈kt〉/kp. For estimating individual rate coefficients, 〈kt〉 and kp, in addition chemically initiated polymerizations have been carried out, in which AMPS conversion was monitored via in-line FT-NIR spectroscopy. The resulting 〈kt〉 and kp values, for 40 °C and an initial AMPS concentration of 2.79 mol·L-1, are 2 × 107 L·mol-1·s-1 and 1 × 105 L·mol-1·s-1, respectively. Both rate coefficients are significantly higher at the lower AMPS content of 1.04 mol·L-1. 〈kt〉 at this lower AMPS content may be understood in terms of termination occurring under reaction diffusion control. The lowering in rate coefficients measured at the higher AMPS content is indicative of a reduced poly(AMPS) chain mobility.