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Issue 8, 2018
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Bis(formylpyrrolyl) cobalt complexes as mediators in the reversible-deactivation radical polymerization of styrene and methyl methacrylate

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Abstract

The combination of [Co(II)2N,O-NC4H3-C(H)[double bond, length as m-dash]O}2(PMe3)2] (1) and tert-butyl-α-bromoisobutyrate (tBiB-Br) is a suitable initiation system for controlling the radical polymerization of styrene, by an atom transfer radical polymerization (ATRP) mechanism, below 70 °C and of methyl methacrylate, by an organometallic mediated radical polymerization (OMRP)/catalytic chain transfer (CCT) interplay mechanism, below 50 °C. The pure ATRP nature of styrene polymerization allowed the synthesis of the polystyrene-b-poly(methyl methacrylate) block copolymer, as confirmed by GPC/SEC and DOSY NMR studies. Attempts to isolate a Co(III) species containing a Br atom (Co(III)–Br), supposedly a key ATRP deactivator, by reacting 1 and tBiB-Br quantitatively afforded the cationic Co(III) complex [Co(III)2N,O-NC4H3-C(H)[double bond, length as m-dash]O}2(PMe3)2]Br (2). Metathetic exchange reactions of complex 2 with TlX gave rise to analogues of the type [Co(III)2N,O-NC4H3-C(H)[double bond, length as m-dash]O}2(PMe3)2]X (3a, X = BF4; 3b, X = BPh4), containing non-coordinating anions. In the absence of a radical initiator, complex 2 mediated the formation of polystyrene and poly(methyl methacrylate), with poor control, likely via a generation of activators by a monomer addition (GAMA) mechanism. Complexes 3a and 3b, however, have been shown to be completely inactive. Addition of 0.5 equivalents of AIBN to 2 drastically improved the molecular weight control in the polymerization of styrene, at 70 °C, through a reverse-ATRP mechanism.

Graphical abstract: Bis(formylpyrrolyl) cobalt complexes as mediators in the reversible-deactivation radical polymerization of styrene and methyl methacrylate

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Publication details

The article was received on 20 Jan 2018, accepted on 27 Feb 2018 and first published on 27 Feb 2018


Article type: Paper
DOI: 10.1039/C8NJ00350E
Citation: New J. Chem., 2018,42, 5900-5913
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    Bis(formylpyrrolyl) cobalt complexes as mediators in the reversible-deactivation radical polymerization of styrene and methyl methacrylate

    T. F. C. Cruz, P. M. M. Machado, C. S. B. Gomes, J. R. Ascenso, M. A. N. D. A. Lemos, J. C. Bordado and P. T. Gomes, New J. Chem., 2018, 42, 5900
    DOI: 10.1039/C8NJ00350E

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