Verdazyl-Mediated Living-Radical Polymerization of Styrene and n-Butyl Acrylate

Abstract

The radical polymerization of styrene and n-butyl acrylate is demonstrated to proceed under controlled conditions between 125 and 130 °C in the presence of either a 1,5-dimethyl-3-phenyl-6-oxoverdazyl radical or a 1,5-dimethyl-3-ethyl-6-oxoverdazyl radical producing polymers with polydispersity indices in the 1.2−1.3 range. While polymerizations initiated with benzoyl peroxide or 1,1-azobis(cyanocyclohexane) in the presence of verdazyl radical were unsuccessful, polymerizations initiated with a styrene/verdazyl unimolecular initiator proceeded in a living fashion, although quite slowly. An increase in polymerization rate was obtained with a 1,5-dimethyl-6-oxoverdazyl radical, producing higher yields of well-defined polymers. The livingness of the resulting styrene and n-butyl acrylate homopolymers is illustrated with chain extension reactions to make well-defined diblock copolymers. These results open a new front in the development of living-radical polymerization processes, and the ability to manipulate the verdazyl structure offers the opportunity to further control and modify this process.

Verdazyl Radicals as Substrates for Organic Synthesis: Unique Access to Tetrahydropyrazolotriazinones, Pyrazolotriazinones and Dihydrotetrazinylacrylonitriles

“…The addition of 1 to the double bond of 1-chloroacrylonitrile was somewhat surprising, since in all our previous work with verdazyl radicals as mediators for living-radical polymerizations, [4] and in our initial cycloaddition studies, [10] this type of reaction was not noticed. In hindsight, given that 5 is a captodative radical, the verdazyl radical addition reaction might have been expected.…”

“…Our interest in verdazyl radicals began with an investigation of their use as mediators for living-radical polymerizations [4] but that focus shifted to exploring whether they could be used as substrates in organic synthesis. In spite of being discovered over 45 years ago, [1a] surprisingly little is known about the chemistry of verdazyl radicals.…”

Recent advances in controlled/living radical polymerization in emulsion and dispersion

“…A number of persistent radicals have been examined as mediators in the SFRP process. They include 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO), [103][104][105] other nitroxides including N-t-butyl-N-(1-diethylphosphono-2,2-dimethylpropyl)nitroxide (called SG1) [106][107][108] and 2,2,5-trimethyl-4-phenyl-3-azahexane-3-nitroxide (TIPNO) and its derivatives 109,110 as well as triazolinyl 111,112 and verdazyl 113,114 stable radicals, employed with free radical initiators to initiate polymerization (Fig. 3).…”

Verdazyls and Related Radicals Containing the Hydrazyl [R2N‐NR] Group

“…6-Oxoverdazyls can also be reduced to the leuco compounds with ascorbic acid, although the reaction is rather sluggish compared to the reduction of nitroxides by this method. 105 1,3,5-Triphenylverdazyl 38 undergoes redox reactions with a variety of organometallic reagents (Scheme 7.17; M = Mg, Li, Al). 106 The verdazyl is initially reduced by the carbanion, producing a Scheme 7.17 metallated (reduced) radical 48 and an alkyl radical.…”