End‐group fidelity of copper(0)‐meditated radical polymerization at high monomer conversion: an ESI‐MS investigation

Abstract

Copper(0)-mediated radical polymerization (single electron transfer-living radical polymerization) is an efficient polymerization technique that allows control over the polymerization of acrylates, vinyl chloride and other monomers, yielding bromide terminated polymer. In this contribution, we investigate the evolution of the end-group fidelity at very high conversion both in the presence and in the absence of initially added copper (II) bromide (CuBr 2 ). High resolution electrospray-ionization mass spectroscopy (ESI-MS) allows determination of the precise chemical structure of the dead polymers formed during the polymerization to very high monomer conversion, including post polymerization conditions. Two different regimes can be identified via ESI-MS analysis. During the polymerization, dead polymer results mainly from termination via disproportionation, whereas at very high conversion (or in the absence of monomer, that is, post-polymerization), dead polymers are predominantly generated by chain transfer reactions (presumably to ligand). The addition of CuBr 2 significantly reduces the extent of termination by both chain transfer and disproportionation, at very high monomer conversion and under post-polymerization conditions, offering a convenient approach to maintaining high end-group fidelity in Cu (0)-mediated radical polymerization. V C 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 49: 5313-5321, 2011 KEYWORDS: atom transfer radical polymerization; end-group fidelity; mass spectrometry; single electron transfer-living radical polymerizationRecently, Percec, Haddleton, and co-workers have demonstrated that Cu(0)-mediated radical polymerization (SET-LRP) displays near perfect bromide end-group fidelity until relatively high conversion (typically 80%) for various monomers in polar solvents, 14,36-44 thus allowing precise synthesis of complex polymer architectures. 24,[45][46][47][48][49][50][51][52][53][54][55] The AGET/ATRP Additional Supporting Information may be found in the online version of this article.

Impact of Competitive Processes on Controlled Radical Polymerization

“…48 Extending further it has been shown that in general, copper(0) mediated polymerization has excellent end group fidelity in comparison to other atom transfer processes. [49][50][51][52] Again, the current model would predict that under conditions of fast deactivation, such is the case in these polymerizations, termination and transfer events, which are typically long time scale, should be reduced with respect to propagation, thus allowing for the ultra high molecular weight polymers with near to 0 mol% termination that have been seen already. Although for acrylates this may be explained simply by the large k p /k t ratio, for vinyl chloride it has been shown that the molecular weight can exceed that of free radical polymerization 45 which can only be the case when molecular weight limiting reactions such as chain transfer to monomer and termination are reduced in comparison to propagation.…”

“…Table 2). 49,52,59 Ultrahigh M w polymers possible with copper(0) mediated radical polymerizations/SETDTLRP 45,50 Low termination rates due to (i) low copper concentrations 60 and (ii) low termination rate coefficients relative to propagation of monomers employed 61,62 High deactivation rate suppresses termination and chain transfer processes…”

o -nitrobenzyl acrylate is polymerizable by single electron transfer-living radical polymerization

“…27,28 For example, SET-LRP is effective for a large panel of monomers such as acrylates, 27,29,30 methacrylates, [31][32][33][34] acrylamides, 35 acrylonitrile, 36 and vinyl chloride. 37,38 This polymerization technique allows high halogen functionality at the chain end, 39 even at high monomer conversion, and is compatible with numerous polar solvents such as dimethyl sulfoxide (DMSO), 26,40 water, 41 alcohols, 42,43 beers, 44 acetic acid, 45 and nonpolar solvent/additives mixtures. 46 More remarkably, Percec and coworkers 47 have demonstrated the controlled polymerization of methyl acrylate (MA) by SET-LRP in the presence of various amount of 4-methoxyphenol, which is a frequently used stabilizer.…”

Aqueous SET-LRP catalyzed with “in situ” generated Cu(0) demonstrates surface mediated activation and bimolecular termination

“…1,2,26,37,38,47 It is important to mention that from many LRP methods that provide polymers with narrow molecular weight distribution, only SET-LRP generates polymers with both narrow molecular weight distribution and quantitative or near quantitative chain-end functionality. 6,7,[48][49][50][51]57,[71][72][73][74][75][76][77] Narrow molecular weight distribution is an important feature of the polymers prepared by LRP but the most significant structural parameter of these polymers is the quantitative or near quantitative chain-end functionality combined with narrow molecular weight distribution. Chain-end functionality is the major parameter of a polymer that allows the construction of complex architectures such as multiple block copolymers, 64,73,[76][77][78][79] and dendrimers by iterative synthesis.…”