Mechanisms and Kinetics of Nitroxide-Controlled Free Radical Polymerization

Abstract

The bulk polymerization of styrene at 125 °C in the presence of a PS−TEMPO adduct was studied with respect to the polymerization rate and the concentration of free TEMPO as a function of time, where PS is polystyrene and TEMPO is 2,2,6,6-tetramethylpiperidinyl-1-oxy. The results were perfectly consistent with the proposed kinetic scheme which assumes the existence of a stationary state with respect to both polymeric and nitroxyl radical concentrations and predicts that the polymerization rate of the nitroxide-mediated system is independent of the adduct concentration, being equal to the polymerization rate of the adduct-free system, i.e., the rate of thermal polymerization in the case of the styrene system studied here. The equilibrium constant K for the PS−TEMPO reversible reaction was estimated to be 2.1 × 10-11 mol L-1 on the basis of the dilatometric and electron spin resonance data. This value of K was indicated to be large enough to set the system under control. This work thus shows that in order for the “living” radical polymerization mediated by a stable nitroxyl radical (SNR) to proceed successfully, a constant supply of initiating radicals (by, e.g., thermal initiation) to make up for the loss of polymer radicals due to irreversible termination is essential as well as the frequent reversible combination of polymeric and nitroxyl radicals. The total number of initiating radicals to be supplied in this way may be small compared with the number of polymer−SNR adducts so that they have no important influence on the molecular weight and its distribution of the product.

Fundamental kinetic aspects of living radical polymerization and the use of gel permeation chromatography to shed light on them

“…Because [P ⅐ ] Ӷ [X ⅐ ] in general, the difference in the quasi-equilibrium from (exact) equilibrium is important. To solve eqs 3 and 4, we here consider the limiting case with R i ӷ 0, first treated by Fukuda et al, 15 and the other limiting case with R i ϭ 0, first treated by Fischer 14 by a different approach than the one 9 given later. For more general cases, see refs.…”

“…15 ). According to eq 2, the concentration of terminated PS radicals, [P] t , is roughly given by [P] …”

Reactions of polystyrene radicals in a monomer-free atom transfer radical polymerization system

“…After purification [11], Br-PS-Br was isolated with M n = 3000 and M w /M n = 1.07 according to PS-calibrated GPC. The initiation efficiency of DBMPM was confirmed to be virtually 100% by 1 H NMR (Fig.…”

“…After purification [11], PS-Br was isolated with M n = 1500 and M w /M n = 1.09. A chain extension test [14] showed that this polymer contains 4% of potentially inactive species (without bromide at the chain end: f dead = 0.04).…”

Nitroxide‐mediated controlled degradation of polypropylene

“…(2001), Matyjaszewski and Davis (2002)). Nitroxide mediated CRP has been studied extensively by many researchers such as Georges et al (1996), Fukuda et al (1996), Georges et al (1997), Georges et al (1998), Wannemacher et al (2003), Braun (2005, and others.…”