Abstract
Polymerization of nonionized acrylic acid (AA) in aqueous solution has been studied via single pulse–pulsed laser polymerization in conjunction with electron paramagnetic resonance spectroscopy. Termination of two types of radicals, secondary chain-end radicals (SPRs) and midchain radicals (MCRs), as well as intramolecular chain transfer (backbiting) of SPRs have been studied between 5 and 40 °C at initial AA concentrations of 10 and 50 wt % in the presence of 15 wt % poly(AA). Predici modeling of the measured SPR and MCR concentration vs time traces after single-pulse initiation at t = 0 yields rate coefficients for backbiting, kbb, and for propagation from an MCR, kpt. These rate coefficients increase toward lower AA-in-water concentration. Estimates for termination of two SPRs, kts,s, and of an SPR and an MCR, kts,t have been obtained by assuming the reported composite-model behavior for acrylates to also hold for acrylic acid polymerization.
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