Controlled radical polymerization of styrene mediated by the C‐phenyl‐N‐tert‐butylnitrone/AIBN pair: Kinetics and electron spin resonance analysis

Abstract

Kinetics of the free radical polymerization of styrene at 110 °C has been investigated in the presence of C‐phenyl‐N‐tert‐butylnitrone (PBN) and 2,2′‐azobis(isobutyronitrile) (AIBN) after prereaction in toluene at 85 °C. The effect of the prereaction time and the PBN/AIBN molar ratio on the in situ formation of nitroxides and alkoxyamines (at 85 °C), and ultimately on the control of the styrene polymerization at 110 °C, has been investigated. As a rule, the styrene radical polymerization is controlled, and the mechanism is one of the classical nitroxide‐mediated polymerization. Only one type of nitroxide (low‐molecular‐mass nitroxide) is formed whatever the prereaction conditions at 85 °C, and the equilibrium constant (K) between active and dormant species is 8.7 × 10−10 mol L−1 at 110 °C. At this temperature, the dissociation rate constant (kd) is 3.7 × 10−3 s−1, the recombination rate constant (kc) is 4.3 × 106 L mol−1 s−1, whereas the activation energy (Ea,diss.), for the dissociation of the alkoxyamine at the chain‐end is ∼125 kJ mol−1. Importantly, the propagation rate at 110 °C, which does not change significantly with the prereaction time and the PBN/AIBN molar ratio at 85 °C, is higher than that for the thermal polymerization at 110 °C. This propagation rate directly depends on the equilibrium constant K and on the alkoxyamine and nitroxide concentrations, as well. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 1219–1235, 2007

Formation Efficiency of ABA Blockcopolymers via Enhanced Spin Capturing Polymerization (ESCP): Locating the Alkoxyamine Function

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In situ nitroxide‐mediated polymerization of styrene promoted by the N‐tert‐butyl‐α‐isopropylnitrone/bpo pair: ESR investigations

“…This might be a limitation for implementation of NMP in industry, especially when process costs are the main criteria to be considered. Therefore, few research groups, both in academia and industry, have contemplated in situ NMP processes,2 thus the direct formation of NMP regulators (nitroxides and alkoxyamines) within the polymerization medium from hopefully cheap (and ideally commercially available) precursors, including nitrones,16, 19–29 nitroso compounds,12, 30, 31 sodium nitrite,11, 32, 33 nitric oxide,12 secondary amines,24, 34, 35 and hydroxylamines 36. In addition to a low cost, these precursors must provide the radical polymerization with a degree of control comparable to preformed nitroxides or alkoxyamines.…”

The nature of Cu(II) species in ATRP: New insights via EPR

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“…A number of publications report on the use of EPR spectroscopy to detect and explore propagating radicals and possible intermediate species, as well as to quantify these radical species. [4][5][6][7][8][9][10] More specifically, EPR has been applied to identify the structure of (meth)acrylate radicals formed in radical polymerization. 6,[11][12][13][14][15][16] One of the most studied and used transition-metal compounds for ATRP is Cu(I)AX, which is oxidized to paramagnetic Cu(II)AX 2 by the aforementioned activation mechanism (Scheme 1).…”