Free radical polymerizations for narrow polydispersity resins: electron spin resonance studies of the kinetics and mechanism

Abstract

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.

Nitroxide decomposition: Implications toward nitroxide design for applications in living free‐radical polymerization

“…The oxidative decomposition of TEMPO during the benzoyl peroxide initiated polymerization of styrene has been found to produce decomposition products by a similar mechanism. [144][145][146] This method of scavenging excess nitroxide during NMP can improve the efficiency of the polymerization by increasing the rate of monomer consumption.…”

The role of mid‐chain radicals in acrylate free radical polymerization: Branching and scission

“…The most notable improvement was the introduction of living/controlled radical polymerization protocols such as reversible addition fragmentation transfer (RAFT) 1,2 polymerization, atom transfer radical polymerization (ATRP), 3 and nitroxide mediated polymerization (NMP). 4,5 These techniques allow for an efficient control over molecular weight and polydispersity over a wide range of conditions and hence provide a very straightforward way to fine tune the polymer product properties. However, despite the high level of control that has been achieved so far, no methods have been found yet to remove the intrinsic obstacles that appear in every free radical polymerization to some extent, for example, transfer to monomer, solvent or polymer reactions.…”

Poly(styrene-co-N-butylmaleimide) macroinitiators by controlled autopolymerization and related block copolymers

“…In recent years initiating systems such as iniferters, [1][2][3][4][5][6][7][8][9][10][11][12] stable free radicals in the presence or absence of peroxides at elevated temperatures, [13][14][15][16][17][18][19][20] or organometallic complexes in association with stable radicals or peroxides 17,21 have become increasingly important in free-radical polymerization. Using these systems, reversibly terminated polymer chains are formed that impart a pseudoliving character to the radical polymerization process.…”