FREE-RADICAL POLYMERIZATIONS FOR NARROW POLYDISPERSITY RESINS - ELECTRON-SPIN-RESONANCE STUDIES OF THE KINETICS AND MECHANISM

Electron spin resonance (ESR) was used to follow the time-dependent concentration of stable TEMPO nitroxide radical in situ to understand the formation of narrow polydispersity, high molecular weight resins by a modified free radical polymerization process. This process involves the reversible termination of growing free radical chains by the TEMPO radicals. The first step is shown to involve a bimolecular reaction of nitroxide radical and benzoyl peroxide (BPO) initiator. This bimolecular reaction, which leads to peroxide radicals, is a rate-promoted decomposition having an activation energy of 40 +/- 5 kJ/mol in toluene, compared to 125 kJ/mol for the thermal decomposition of BPO to its radicals. Computer simulations were used to numerically solve the reaction kinetics. ESR has shown that the rate of nitroxide radical disappearance in styrene polymerization is consistent with reversible termination of growing chains by the nitroxide radical, affording a pseudoliving polymer system.