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 degrees 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, k(bb), and for propagation from an MCR, k(p)(t). These rate coefficients increase toward lower AA-in-water concentration. Estimates for termination of two SPRs, k(t)(s,s), and of an SPR and an MCR, k(t)(s,t) have been obtained by assuming the reported composite-model behavior for acrylates to also hold for acrylic acid polymerization.