Living diradical polymerization

Abstract

A diradical initiator containing two thermoreversible bonds was prepared and used for the polymerization of styrene at 90 "C. The monomer consumption and the variation of the molecular weight were monitored with time. The results show that the process can be considered as living and that the polymerization rate is independent of the radical initiator concentration. By elemental analysis of the chain ends it was concluded that the propagation reaction occurs at both ends.

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

“…7 In organic chemistry, nitroxides have been used in kinetic studies, [8][9][10][11] as oxidizing species in the form of the corresponding N-oxo ammonium salts, [12][13][14][15][16][17][18][19][20][21][22][23] as temporary caps for transient carbon radicals, [24][25][26][27][28][29][30][31] and as probes for stereocontrol with prochiral carbon radicals. [32][33][34][35][36] In polymer chemistry, nitroxide-mediated polymerization (NMP) [37][38][39][40][41][42][43][44][45][46][47] has become popular as a method for preparing living polymers [48][49][50][51] under mild, chemoselective conditions with good control over both the polydispersity and molecular weight. In designing nitroxides for applications in NMP, much attention has been directed toward fine-tuning the nitroxide structure to lower the bond dissociation energy (BDE) of the transient Nalkox...…”

Product Class 5: Hydroxylamines

“…Radical trapping of nitroxides provides an elegant access to O,N,N-trisubstituted hydroxylamines, which by their own serve as initiators or regulators in nitroxide-mediated radical polymerization. [733][734][735][736][737][738] For example, the reaction of bis(trifluoromethyl) nitroxide with toluene produces O-benzyl-N,N-bis(trifluoromethyl)hydroxylamine (527) in 65% yield (Scheme 219). Analogously, benzyl cyanide can be converted into hydroxylamine 528 in 96% yield, and isobutene reacts with bis(trifluoromethyl) nitroxide to give hydroxylamine 529 in 84% yield.…”

A detailed mechanistic study of bulk MADIX of styrene and its chain extension

“…The EGF data are reliably measured by consecutively performing dialysis to remove residual OEXEP and elemental analysis to determine the sulphur and nitrogen content for the polymer samples. It should be noted that, in general, EGF determination is challenging, 62 especially for high molar mass polymers for which the accuracy of techniques such as proton nuclear magnetic resonance ( 1 H-NMR), [63][64][65][66][67][68] ultraviolet (UV) spectroscopy, 69,70 matrixassisted laser desorption/ionization time-of-flight, 61,62,71,72 and even elemental analysis 73 is limited. The modelling tools are used to understand better the MADIX mechanism and to visualize -for the first time -the monomer sequences along individual chains during chain extension with (i) styrene or (ii) n-butyl acrylate (nBuA).…”