Observations of Initial Steps of Radical Polymerizations by Time-Resolved and Steady-State Electron Spin Resonance Spectroscopy with the Aid of ATRP

摘要

The initial steps of conventional radical polymerizations were investigated by both steady-state electron spin resonance (SS ESR) spectroscopy in combination with atom transfer radical polymerization (ATRP) technique and with time-resolved ESR (TR ESR) spectroscopy. The SS ESR/ATRP combination method can observe each initiation step by measurements of uniform oligomeric model propagating radicals. TR ESR spectra allowed direct observation of transient radicals (chain initiating radical) obtained by the addition reaction of a diphenylphosphinoyl radical to vinyl monomers. The addition rate constants (k_2) and activation energies (E_a) of diphenylphosphinoyl radical to the (meth)acrylates (initiation rate constants) were determined based on the TR ESR spectra. A combination of steady-state ESR and TR ESR provids information on both the initiation and propagation processes in radical polymerization of (meth)acrylates.