Low-Temperature Preparations of Unimolecular Nitroxide Initiators for “Living” Free Radical Polymerizations

Abstract

Low-temperature methods for the preparation of monomeric initiators for use in “living” free radical olefin polymerizations have been developed. Oxidative methods for generating carbon radicals in the presence of nitroxide traps such as TEMPO utilize PbO2 with benzylic, alkyl, or phenylhydrazines or CuCl2 with lithium enolates. Photolytic methods employ [Cp(CO)2Fe]2 with a benzylic bromide, diphenyl disulfide with styrene, or di-tert-butyl peroxide with ethers. The use of di-tert-butyl hyponitrite with ethers generates carbon radicals at 50 °C that are trapped by TEMPO.

A novel method for the synthesis of alkoxyamine initiators for nitroxide-mediated radical polymerization using Mn(OAc)3 as electron-transfer reagent

“…Many efforts were undertaken to synthesize unimolecular alkoxyamine initiators based on radical trapping reactions [6][7][8][9][10][11] and on nucleophilic substitution methods [5,12]. However, it is still difficult to synthesize alkoxyamines with a variety of functional groups.…”

Controlled Photoradical Polymerization Mediated by 2,2,6,6-Tetramethylpiperidine-1-Oxyl

“…monomers [17][18][19][20][21]; however, the scope of the applicable monomers has been extended by improving the structure of the nitroxide [22][23][24] using alkoxyamine adducts [25,26] and utilizing additives [27,28]. The NMP still has advantages in using nonmetallic catalysts, thus creating a great variety of architectures through designing the nitroxide catalysts, and producing uncolored or less-colored polymers.…”

2-tert-Butoxy-1-phenyl-1-(2,2,6,6-tetramethylpiperidin-1-yloxy)ethane

“…This alkoxyamine should be prepared separately and then added in a known concentration to the monomer to be polymerized. Synthetic routes to alkoxyamines include the trapping of alkyl radicals by free nitroxides at moderate temperatures (Braslau et al, 1997;Miura et al, 1998) and a catalytic route involving Mn-salen complexes [H 2 salen is bis(salicylidene)ethylenediamine; Dao et al, 1998]. The title compound, (I), has been synthesized in the course of these studies (Cameron et al, 2000).…”