Communication Macromolecular Rapid Communications Macromol. Rapid Commun. 2012, 33, 152−157 © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim wileyonlinelibrary.com 152 DOI: 10.1002/marc.201100590 1. Introduction Nitroxide-mediated polymerization (NMP) has experi- enced fast development in several directions: preparation of new and more efficient initiators, [1–4] kinetic investi- gations, [5–8] preparation of new materials, [9–11] and new applications. [3,11,12] The kinetic process can be grossly described as displayed in Scheme 1. [7] It mainly relies on the equilibrium between the alkoxyamine C—ON bond homolysis ( k d of the dormant species) that leads to the alkyl and nitroxyl radicals and their fast recombination ( k c ), which maintains the self-termination reactions ( k t ) at very low level allowing the propagation of the poly- meric species ( k p ). Although NMP is efficient for most of activated monosubstituted monomers, the NMP of 1,1-disubstituted monomers such as methyl methacrylate is still a challenge to perform. Furthermore, in several cases, the same alkoxyamine is not suitable for the copo- lymerization of different monomers, or when one shifts from bulk polymerization to either polymerization of hydrophylic monomers or polymerization in an aqueous medium. One way to overcome these drawbacks would be to develop new readily tunable alkoxyamines. We have recently reported that protonation of the nitroxyl fragment decreases k d as a function of the pH, [13] and that protonation of the alkyl fragment in an organic solvent increases k d . [14] Hereafter, we present the pH dependence of the k d of 1 (Scheme 2), density functional theory (DFT) calculations unveiling the effects involved in the increase in k d , and applications to NMP of styrene and sodium sty- rene sulfonate. In recent work, a 15-fold increase in the C–ON bond homolysis rate constant k d of 4-pyridylethyl-SG1-based alkoxyamine was observed upon protonation of the pyridyl moiety in organic solvent. In this report, the pH dependence of k d (p K a = 4.7) is investigated in D 2 O/CD 3 OD (v/v 1:1). A 64-fold increase in k d is observed at acidic pH. Calculations show that the increase in k d upon protonation is due to both an increase in the stabilization of the protonated 4-pyridylethyl radical and an increase of the destabilization of the starting materials through an increase in the polarity of the alkyl fragment. This new alkoxyamine is applied to NMP of styrene and sodium styrene sulfonate. Chemically Triggered C–ON Bond Homolysis in Alkoxyamines. Part 2: DFT Investigation and Application of the pH Effect on NMP Elena Bagryanskaya, Paul Brémond, Mariya Edeleva, Sylvain R. A. Marque,* Dmitriy Parkhomenko, Valérie Roubaud, Didier Siri 0 500 1000 1500 2000 2500 3000 3500 4000 -4.0 -3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 k d =1.6 10 -2 s -1 ln(C/C 0 ) time (s) k d =2.5 10 -4 s -1 N P(O)(OEt)2 O N * * 1 N P(O)(OEt)2 O N D, Cl 1H+ H Prof. E. Bagryanskaya, Dr. M. Edeleva, D. Parkhomenko International Tomography Center, Institutskaya 3A, 630090 Novosibirsk, Russia Dr. P. Brémond, Prof. S. R. A. Marque, Dr. V. Roubaud, Prof. D. Siri Aix-Marseille Université, case 521, Avenue Escadrille Normandie-Niemen, 13397 Marseille cedex 20, France E-mail: sylvain.marque@univ-provence.fr Scheme 1 . Simplified scheme of NMP. k t M n+1 O N RM n + N O + M k d k c self termination products dormant species active species k p