Time-resolved electron spin resonance spectroscopy of radicals formed during free radical polymerizations of alkyl acrylates.

Time-resolved electron spin resonance (TR ESR) spectra allows direct observation of transient radicals (primary propagating radicals) obtained by the addition reaction of a diphenylphosphinoyl radical to acrylates. The addition rate constants (k(2) ) of the diphenylphosphinoyl radical to the acrylates (initiation rate constants) were determined by the monomer concentration dependence of the decay rate of the diphenylphosphinoyl radical. The value of k(2) was 1.9 × 10(7)  s(-1)  · M(-1) for the case of t-butyl acrylate, while the k(2) values of ethyl, n-butyl, 2-ethylhexyl, and dodecyl acrylates were about 1 × 10(7)  s(-1)  · M(-1) . A combination of steady state ESR and TR ESR provided information on the kinetics both of initiation and propagation processes in the radical polymerization of acrylates.