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 co ncentration of stable TEMPO nitroxide radical in situ to understand th e 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 o f nitroxide radical and benzoyl peroxide (BPO) initiator. This bimolec ular reaction, which leads to peroxide radicals, is a rate-promoted de composition having an activation energy of 40 +/- 5 kJ/mol in toluene, compared to 125 kJ/mol for the thermal decomposition of BPO to its ra dicals. Computer simulations were used to numerically solve the reacti on kinetics. ESR has shown that the rate of nitroxide radical disappea rance in styrene polymerization is consistent with reversible terminat ion of growing chains by the nitroxide radical, affording a pseudolivi ng polymer system.