Role of the alkyl fragment of initiating alkoxyamine in nitroxide mediated polymerization of styrene

Abstract

The role of the alkyl fragment of alkoxyamine initiating the homopolymerization of styrene is experimentally and theoretically studied in the case of 2,2,6,6 tetramethylpiperidine 1 oxyl derivatives. The rate constants of homolysis and recombination are measured for the alkoxyamines under study. The charac teristics of polymerization initiated by these compounds are experimentally examined. The kinetics of poly merization is theoretically calculated with allowance for the measured kinetic parameters and the experimen tally detected side reaction of hydrogen atom transfer to the nitroxide radical during the thermolysis of alkoxyamine 2 cyano 2 isopropyl-TEMPO.

Kinetic Modeling as a Tool to Understand and Improve the Nitroxide Mediated Polymerization of Styrene

“…To validate this assumption, simulations have been performed using a difference in reactivity of one order of magnitude between the initiator radicals and the propagating radicals for the addition to styrene. In agreement with the experimental findings reported by Zubenko et al [32] and by Ananchenko et al, [30,31] the simulations revealed no influence of the first addition of the initiator radical on the kinetics of the NMP of styrene in the presence of TEMPO-1-phenylethyl or SG1-1-phenylethyl. Using kinetic modeling, also the importance of chain transfer to trimer has been assessed and was found to be insignificant in the conditions studied in this work.…”

“…[56] As pointed out by Bagryanskaya et al, [64] the addition of the initiator radical can play an important role in the NMP of styrene if it competes with the H-transfer side reaction between the initiator radical and the nitroxide. However, experimental studies reported by Zubenko et al [32] and by Ananchenko et al [30,31] have shown that for the alkoxyamines considered in this work, i.e., TEMPO-1-phenylethyl, TEMPO-polystyrene, SG1-1-phenylethyl, SG1-polystyrene, the H-transfer reaction between the initiator radical and the nitroxide is unimportant. It can thus be expected that the addition of the initiator radical to styrene will not play a crucial role in the kinetics of the polymerization of styrene in the presence of TEMPO-1-phenylethyl or SG1-1-phenylethyl (see further).…”

“…Transfer reactions from radicals to TEMPO-H, regenerating the nitroxide, have been studied by Gridnev [33] and Zubenko et al [32] Based on simplified kinetic models, these authors reported values of 3: [33] and 0:2 m 3 Á mol À1 Á s À1 . [32] Using kinetic modeling, the importance of transfer reactions involving hydroxylamine has been assessed and found to be insignificant in the conditions studied in this work.…”

“…The same order of magnitude for these rate coefficients has been reported by Marque et al [42] and by Benoit et al [26] For the deactivation of polystyryl radicals by SG1, Guillaneuf et al [73] have reported a value of Besides the previous key NMP reactions, side reactions involving the nitroxide, such as transfer from nitroxide to monomer (tr xm ) and to dimer (tr xd ) [34] and disproportionation, can occur. However, according to literature, [30][31][32] disproportionation involving nitroxide in systems containing EMPO-1-phenylethyl, TEMPO-polystyrene, SG1-1-phenylethyl, and SG1-polystyrene can be neglected. .…”

“…[1,5] Recently, the focus of NMP research has shifted to the development of other nitroxides, such as N-(2-methyl-2-propyl)-N-(1-diethylphosphono-2,2-dimethylpropyl)-N-oxyl [DEPN, also known as SG1; Figure 2(b)], [9,[26][27][28][29] that lead to higher polymerization rates and that also enable the controlled NMP of other monomers, such as acrylates. [1] Several side reactions can interfere with the NMP activation/deactivation, such as alkoxyamine decomposition yielding terminally unsaturated polymer and hydroxylamine, [30][31][32] chain transfer to the thus formed hydroxylamine, [33] transfer reactions involving the nitroxide, [34] and nitroxide decomposition. [9,35] For styrene, the NMP is typically performed at temperatures above 373 K, and a further complication arises due to the occurrence of thermal initiation through the Mayo mechanism ( Figure 3) by which initiator radicals are continuously generated.…”