Controlled/living polymerization of methyl methacrylate using new sterically hindered imidazoline nitroxides prepared via intramolecular 1,3-dipolar cycloaddition reaction

Abstract

A series of imidazoline nitroxides with bulky spirocyclic moieties at the positions 2 or 5 of imidazole ring were synthesized using intramolecular 1,3-dipolar cycloaddition in 2Himidazole 1-oxides or 4H-imidazole 3-oxides with pent-4-enyl groups followed by isoxazolidine ring opening and oxidation. Capability of the nitroxides to control radical polymerization of methyl methacrylate (MMA) and styrene was investigated. For that purpose, alkoxyamines were synthesized from the aforementioned nitroxides and tert-butyl a-bromoisobutyrate. Homolysis rate constants of the alkoxyamines were measured and possible contributions of side reactions were quantified.Nitroxide-mediated polymerization of styrene and MMA was studied using the alkoxyamines as initiators. MMA polymerization was found to proceed in controlled regime up to 55% of monomer conversion and the polymer obtained was able to reinitiate the polymerization of styrene. Quota of "living" chains estimated to reach 90%. V C 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 929-943 Additional Supporting Information may be found in the online version of this article.

Synthesis of 1-azaspiro[4.4]nonan-1-oxyls via Intramolecular 1,3-Dipolar Cycloaddition

“…We have recently reported on similar reversibility of intramolecular cyclization of sterically shielded pent-4-enylnitrone of 2H-imidazole series [15]. We have previously reported that H2O2/WO4 2system is inefficient for the oxidation of secondary amines with spiro-(2-hydroxymethyl)-cyclopentane moiety at α-carbon to nitroxides, while this oxidation can be easily performed using m-CPBA [6,15].…”

Nitroxide‐Mediated Polymerization of Methacrylic Esters: Insights and Solutions to a Long‐Standing Problem

“…Considering previous results showing that a sterically hindered imidazoline nitroxide has a low k cD value but also a low stability, several imidazoline nitroxides and their corresponding alkoxyamines bearing a spiro cyclic moiety were prepared via 1,3‐dipolar cycloaddition reaction, enabling the facile synthesis of a library of compounds (Figure a) . The fraction of disproportionation was found to be low (1.3–3%), making these materials potential initiators for NMP of methacrylic esters.…”

“…b) Evolution of M n and D‐ with monomer conversion for NMP of MMA initiated with an ethyl‐based alkoxyamine at 80 °C with a monomer‐to‐initiator ratio of 800:1. Reproduced with permission …”

The X-ray investigation of the macro-stresses and design for its realization (laboratory practicum)

“…The processes belonging to the first group are based on the reaction of a reversible polymerization break during the interaction of a growing radical with specially introduced regulating agents (Scheme 1). These include polymerization by the mechanism of reversible inhibition [27][28][29] and atom transfer polymerization [25,[30][31][32]. The second group of methods includes processes in which the exchange between active and dormant chains occurs due to degenerate chain transfer:…”

“…As is known [27][28][29], one of the directions of the CRP in terms of the mechanism of reversible inhibition is associated with the use of nitroxyl radicals generated in situ (directly in the reaction system) from available precursors to control the polymerization. The indicated approach was successfully used for the synthesis of AN copolymers [78].…”