Re‐formation Reaction of Cyclic Nitroxide‐Based Alkoxyamines: Steric and Polar/Stabilization Effects

In nitroxide‐mediated radical polymerization, the polymerization times decrease with the increasing re‐formation rate constant of the C? ON bond (→ alkoxyamine) between the growing polymer chain and the nitroxide radical. The factors influencing the re‐formation rate constant are of considerable interest, but up to now, the polar/stabilization effects have not been addressed thoroughly. The combination of new data with previously reported data now showed that the re‐formation rate constant k_c increases with the increasing polar character of the substituents attached to the nitroxide moiety. The polar/stabilization effects are weaker for the re‐formation than for the homolysis of the C? ON bond, and may be mainly attributed to the relocation of the odd electron onto the O‐atom of the N? O moiety, i.e., the stabilization of the nitroxide moiety. Hence, it is possible to predict the values of k_c by combining both the polar/stabilization (σ_I) and steric effects (E ), i.e., log(k_c/M ^?1 s^?1) = 9.86 + 0.57 ? σ_I + 0.40 ? E_s.     

Incubation period in the 2,2,4,4‐tetramethyl‐1‐piperidinyloxy‐mediated thermal autopolymerization of styrene: Kinetics and simulations

Mechanisms and simulations of the induction period and the initial polymerization stages in the nitroxide‐mediated autopolymerization of styrene are discussed. At 120–125 °C and moderate 2,2,4,4‐tetramethyl‐1‐piperidinyloxy (TEMPO) concentrations (0.02–0.08 M), the main source of radicals is the hydrogen abstraction of the Mayo dimer by TEMPO [with the kinetic constant of hydrogen abstraction (k_h)]. At higher TEMPO concentrations ([N?] > 0.1 M), this reaction is still dominant, but radical generation by the direct attack against styrene by TEMPO, with kinetic constant of addition k_ad, also becomes relevant. From previous experimental data and simulations, initial estimates of k_h ≈ 1 and k_ad ≈ 6 × 10^?7 L mol^?1 s^?1 are obtained at 125 °C. From the induction period to the polymerization regime, there is an abrupt change in the dominant mechanism generating radicals because of the sudden decrease in the nitroxide radicals. Under induction‐period conditions, the simulations confirm the validity of the quasi‐steady‐state assumption (QSSA) for the Mayo dimer in this regime; however, after the induction period, the QSSA for the dimer is not valid, and this brings into question the scientific basis of the well‐known expression k_th[M]³ (where [M] is the monomer concentration and k_th is the kinetic constant of autoinitiation) for the autoinitiation rate in styrene polymerization. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6962‐6979, 2006     

9‐Bromoanthracene photodimers as initiators in controlled radical polymerization: Silane radical atom abstraction coupled with nitroxide mediated polymerization

Slow initiation relative to propagation has previously prevented photodimers of 9‐bromoanthracene or 9‐chloroanthracene, formed by [4 + 4] photocyclization reactions of the analogous 9‐haloanthracene, from being viable initiators in atom transfer radical polymerization (ATRP) reactions. The resulting polymers were found to possess high polydispersity index (PDI) values, much higher than expected number average molecular weight (M_n) values, with the reaction displaying a nonlinear relationship between monomer conversion and M_n. We report here the use of silane radical atom abstraction (SRAA) to create initiating bridgehead radicals in the presence of 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) to mediate the polymerization. When using SRAA coupled with nitroxide mediated polymerization, a dramatic decrease in PDI values was observed compared with analogous ATRP reactions, with M_n values much closer to those anticipated based on monomer‐to‐initiator ratios. Analysis using UV‐Vis spectroscopy indicated only partial anthracene labeling (～ 25%) on the polymers, consistent with thermolysis of the anthracene photodimer coupled with competition between initiation from the bridgehead photodimer radical and silane‐based radical. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6016–6022, 2008     

Intramolecular Hydrogen Bonding: The Case of β‐Phosphorylated Nitroxide (= Aminoxyl) Radical

Alkoxyamines and persistent nitroxide (= aminoxyl) radicals are important regulators of nitroxide‐mediated radical polymerization. Since polymerization times decrease with the increasing homolysis rate constant of the C? ON bond homolysis between the polymer chain and the aminooxy moiety, the factors influencing the cleavage rate constant are of considerable interest. It has already been shown that the value of the homolysis rate constant k_d is very sensitive to the stabilization of both released radical species. X‐Ray, EPR, and kinetic data showed that the intramolecular H‐bonding radical in the 1‐(diethoxyphosphoryl)‐2,2‐dimethylpropyl 2‐hydroxy‐1,1‐dimethylethyl nitroxide ( 3a ) (homologue of 2‐hydroxy‐1,1‐dimethylethyl 1‐phenyl‐2‐methylpropyl nitroxide ( 2a )) did not occur with the nitroxide moiety as expected but with the phosphoryl group. However, the polymerization rate of styrene (= ethenylbenzene) was significantly enhanced.     

Reaction of H and D atoms with deuterated propylenes

Effects of deuterium substitution in propylene on the relative rates of H(D) atom abstraction from and addition to the olefin, and on the orientation of H(D) atom addition, have been studied in the gas phase at room temperature. Effects of isotopic substitution of the olefinic hydrogen atoms on abstraction could not be observed, but abstraction is reduced five- to tenfold by deuteration of the methyl group. Deuteration of either olefinic position enhances the rate of addition to the substituted carbon atom. Disproportionation-combination ratios for deuterium-substituted propyl radicals are not greatly different from those for unsubstituted radicals, the largest effect being for C₃D₇ radicals, for which the overall k_d/k_c is reduced 10–15%.     

Spin Trapping of Radical Intermediates Generated by the Oxidation of Substituted 4‐Methylphenols

A series of substituted 4‐methylphenols 1 and 2 was oxidized with PbO₂ in the presence of nitroso compounds 3 – 10 . The formation of adducts of benzyl radicals with the nitroso spin traps in the reaction mixture was established, suggesting the abstraction of an H‐atom from the methyl substituent of 1 or 2 . In the consecutive steps, the adducts underwent a further rearrangement to the corresponding nitrones. When the starting phenol contained bulky ^tBu groups in ortho‐position (see 2,6‐di(tert‐butyl)‐4‐methylphenol ( 1a )), the stable 2,6‐di(tert‐butyl)‐4R‐phenoxy radicals (R=? CH?N⁺(O^?)? X) were detected as the final radical products. The indirect evidence of nitrones in the reaction mixture was performed in one case by the reaction with a RO radicals.     

Kinetics and mechanism of the autoxidation of pentaerythrityl tetraheptanoate at 180–220°C

A kinetic and mechanistic study of the autoxidation of liquid pentaerythrityl tetraheptanoate (PETH) at 180–220°C has been carried out utilizing a stirred-flow reactor. The results are consistent with the occurrence of a chain reaction scheme similar to that proposed for n-hexadecane autoxidation, namely, the formation of monohydroperoxides by the intermolecular abstraction reaction (3), the formation of α,γ- and α,δ-dihydroperoxides and α,γ- and α,δ-hydroperoxyketones by intramolecular peroxy radical abstraction reactions (4) and (4*), the bimolecular termination of peroxy radicals, reaction (6), and the rapid conversion of α,γ-hydroperoxyketones to the corresponding cleavage acids and methyl ketones, reaction (7). Comparisons of various rate parameters for the n-hexadecane and PETH systems reveal that the values of k₇ and (k₃/H atom)/(2 k₆)^1/2 are within experimental uncertainties identical for the two systems at 180°C. The proposed reaction scheme includes the concurrent formation of hydroxy radicals and hydroperoxyketone species. The results of kinetic analysis and the experimentally observed isomer distributions of primary and secondary monohydroperoxide products at high and low oxygen pressures suggest that ≈60% of the hydrogen abstractions from PETH at high oxygen pressures occur by hydroxy radicals.     

Reaction of Aromatic Peroxyl Radicals with Alkynes: A Mass Spectrometric and Computational Study Using the Distonic Radical Ion Approach

The reaction of the aromatic distonic peroxyl radical cations N‐methyl pyridinium‐4‐peroxyl (PyrOO^.+) and 4‐(N,N,N‐trimethyl ammonium)‐phenyl peroxyl (AnOO^.+), with symmetrical dialkyl alkynes 10a – c was studied in the gas phase by mass spectrometry. PyrOO^.+ and AnOO^.+ were produced through reaction of the respective distonic aryl radical cations Pyr^.+ and An^.+ with oxygen, O₂. For the reaction of Pyr^.+ with O₂ an absolute rate coefficient of k₁=7.1×10^?12 cm³ molecule^?1 s^?1 and a collision efficiency of 1.2 % was determined at 298 K. The strongly electrophilic PyrOO^.+ reacts with 3‐hexyne and 4‐octyne with absolute rate coefficients of k_hexyne=1.5×10^?10 cm³ molecule^?1 s^?1 and k_octyne=2.8×10^?10 cm³ molecule^?1 s^?1, respectively, at 298 K. The reaction of both PyrOO^.+ and AnOO^.+ proceeds by radical addition to the alkyne, whereas propargylic hydrogen abstraction was observed as a very minor pathway only in the reactions involving PyrOO^.+. A major reaction pathway of the vinyl radicals 11 formed upon PyrOO^.+ addition to the alkynes involves γ‐fragmentation of the peroxy O? O bond and formation of PyrO^.+. The PyrO^.+ is rapidly trapped by intermolecular hydrogen abstraction, presumably from a propargylic methylene group in the alkyne. The reaction of the less electrophilic AnOO^.+ with alkynes is considerably slower and resulted in formation of AnO^.+ as the only charged product. These findings suggest that electrophilic aromatic peroxyl radicals act as oxygen atom donors, which can be used to generate α‐oxo carbenes 13 (or isomeric species) from alkynes in a single step. Besides γ‐fragmentation, a number of competing unimolecular dissociative reactions also occur in vinyl radicals 11 . The potential energy diagrams of these reactions were explored with density functional theory and ab initio methods, which enabled identification of the chemical structures of the most important products.     

Chlorine substitution promotes phenyl radical loss from C8‐phenoxy‐2′‐deoxyguanosine adducts: implications for biomarker identification from chlorophenol exposure

Chlorophenols are persistent organic pollutants, which undergo peroxidase‐mediated oxidation to afford phenolic radical intermediates that react at the C8‐site of 2′‐deoxyguanosine (dG) to generate oxygen‐linked C8‐dG adducts. Such adducts are expected to contribute to chlorophenol toxicity and serve as effective dose biomarkers for chlorophenol exposure. Electrospray ionization mass spectrometry (ESI‐MS) was employed to study collision induced dissociation (CID) for a family of such phenolic O‐linked C8‐dG adducts. Fragmentation of the deprotonated nucleosides demonstrates that an unexpected homolytic cleavage of the ether linkage to release phenyl radicals and a nucleoside distonic ion with m/z 281 competes effectively with commonly observed breakage of the glycosidic bond to release the deprotonated nucleobase. Increased chlorination of the phenyl ring enhances phenyl radical loss. Density functional theory calculations demonstrate that Cl‐substitution decreases phenyl radical stability but promotes homolytic breakage of the C8–phenyl bond in the C8‐dG adduct. The calculations suggest that phenyl radical loss is driven by destabilizing steric (electrostatic repulsion) interactions between the ether oxygen atom and ortho‐chlorines on the phenyl ring. The distonic ion at m/z 281 represents a unique dissociation product for deprotonated O‐linked C8‐dG adducts and may prove useful for selective detection of relevant biomarkers for chlorophenol exposure by tandem mass spectrometry using selective reaction monitoring. Copyright © 2015 John Wiley & Sons, Ltd.     

A difference of six orders of magnitude: A reply to “the magnitude of the fragmentation rate coefficient”

There has been an ongoing debate regarding the mechanism that causes rate retardation phenomena observed in some reversible addition‐fragmentation transfer (RAFT) polymerization systems. Some attribute the retardation to slow fragmentation of adduct radicals, others attribute it to fast fragmentation coupled with cross‐termination between propagating and adduct radicals. There exists a difference of six orders of magnitude (10^?2 versus 10⁴/s) in the reported values of the fragmentation rate constant (k_f0) for virtually similar RAFT systems of PSt? S? C · (Ph)? S? PSt. In this communication, we explain the estimates of k_f ～ 10⁴/s and the choices of the rate constant in modeling based on experimental polymerization rate and radical concentration data. The use of k_f ～ 10^?2/s in the model results in a calculated adduct radical concentration level of 10^?4 to 10^?3 mol/L, which appears to directly contradict the reported electron spin resonance (ESR) data in the range of <10^?6 mol/L. We hope that this open discussion can stimulate more effort to resolve this outstanding difference. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 2833–2839, 2003     

Reaction kinetics and thermochemistry of the chemically activated and stabilized primary ethyl radical of methyl ethyl sulfide,CH3SCH2CH2•, with O2 to CH3SCH2CH2OO•

Oxidation of methyl ethyl sulfide (CH₃SCH₂CH₃, methylthioethane, MES) under atmospheric and combustion conditions is initiated by hydroxyl radicals, MES radicals, generated after loss of a H atom via OH abstraction, will further react with O₂ to form chemically activated and stabilized peroxyl radical adducts. The kinetics of the chemically activated reaction between the CH₃SCH₂CH₂• radical and molecular oxygen are analyzed using quantum Rice-Ramsperger-Kassel theory for k(E) with master equation analysis and a modified strong-collision approach to account for further reactions and collisional deactivation. Thermodynamic properties of reactants, products, and transition states are determined by the B3LYP/6-31+G(2d,p), M062X/6-311+G(2d,p), ωB97XD/6-311+G(2d,p) density functional theory, and CBS-QB3, G3MP2B3, and G4 composite methods. The reaction of CH₃SCH₂CH₂• with O₂ forms an energized peroxy adduct CH₃SCH₂CH₂OO• with a calculated well depth of 34.1 kcal mol⁻¹ at the CBS-QB3 level of theory. Thermochemical properties of reactants, transition states, and products obtained under CBS-QB3 level are used for calculation of kinetic parameters. Reaction enthalpies are compared between the methods. The temperature and pressure-dependent rate coefficients for both the chemically activated reactions of the energized adduct and the thermally activated reactions of the stabilized adducts are presented. Stabilization and isomerization of the CH₃SCH₂CH₂OO• adduct are important under high pressure and low temperature. At higher temperatures and atmospheric pressure, the chemically activated peroxy adduct reacts to new products before stabilization. Addition of the peroxyl oxygen radical to the sulfur atom followed by sulfur-oxygen double bond formation and elimination of the methyl radical to form S(= O)CCO• + CH₃ (branching) is a potentially important new pathway for other alkyl-sulfide peroxy radical systems under thermal or combustion conditions.     

DFT and MP2 molecular orbital determination of OH–toluene–O2 isomeric structures in the atmospheric oxidation of toluene

We have performed an exhaustive theoretical study, using a density functional theory (DFT) and ab initio techniques, of the possible isomers of the OH–toluene–O₂ radical. DFT calculations of the all electron type using the hybrid B3LYP approach and 6‐31G* orbital basis set were employed. In addition to the well‐established ortho position, addition of OH at C₁ on the benzene ring of toluene was also considered for the initial methylhydroxycyclohexadienyl adduct. In all, 28 different intermediate structures of the OH–toluene–O₂ system, consisting of peroxyl radicals, bicyclic structures, and epoxides, have been explored through fully optimized electronic structure calculations. Starting from the 1,3‐O₂‐methylorthohydroxycyclohexadienyl radical, or ortho‐OH adduct, several peroxyl radicals are found to have low‐lying structures contained within a small energy range (about 1 kcal/mol). Only two bicyclic structures are stable with respect to the methylhydroxycyclohexadienyl radical plus O₂, one of them being clearly favored. The four possible epoxy structures are all found to lie more than 15 kcal/mol lower than any of their peroxyl and bicyclic isomers. The preference, first noted by Bartolotti and Edney, for structures in which the OH group lies on the same side of the ring as the O₂ group, is obeyed in all cases. If the 1‐CH₃, 1‐OH cyclohexadienyl radical (or C₁–OH adduct) is used as the initial adduct, three peroxyl radicals are expected to be formed, while two bicyclic structure and three epoxides need to be considered. These structures are found to be, in general, less stable than the ones arising from the ortho adduct. However, the 4‐O, 2,3‐epoxy, 1,1‐methylhydroxycyclohexadienyl radical is found to be the most stable of all the isomers considered, and this, by more than 3 kcal/mol. In this work, most structures were also calculated with the MP2 method with a 6‐31G* basis set. The geometries obtained with the two methods are similar. Contrary to the B3LYP method, MP2 always yields an extra stability to structures in which the C₁ carbon atom has sp³ hybridization. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 716–730, 2000     

A Study of the Nitroso Spin Adducts of the Pentacarbonyl Rhenium Radical

Nitrosobenzene (NB) and nitroso-tetr-butane (NtB) were used to trap the photogenerated rhenium pentacarbonyl radical. Self trapped radicals and spin adducts were studied in detail by EPR spectroscopy. In methylene chloride, both nitroxide and anilino spin adducts can be observed with NtB at ?30°. In contrast, only the nitroxide spin adduct of nitrosobenzene was observed in either hexane, or methylene chloride solution. This solvent controlled spin adduct chemistry, can be explained in terms of the solute-solvent interaction.     

β‐Hydrogen transfer from poly(methyl methacrylate) propagating radicals to the nitroxide SG1: Analysis of the chain‐end and determination of the rate constant

Methyl methacrylate (MMA) was polymerized in bulk at 70 °C in the presence of an alkoxyamine initiator with low dissociation temperature (the so‐called BlocBuilder?) and increasing amounts of free N‐tert‐butyl‐N‐(1‐diethylphosphono‐2,2‐dimethylpropyl) nitroxide (SG1). Low final monomer conversions were reached, indicating a loss in radical activity due to side reactions such as irreversible homoterminations between the propagating radicals and β‐hydrogen transfer (also called disproportionation) from a propagating radical to a free‐SG1 nitroxide. Proton NMR and MALDI‐TOF mass spectrometry were used to analyze the polymer chain‐ends and to clearly identify the main mechanism of irreversible termination. In particular, it was shown that all polymer chains were terminated by an alkene function in the presence of a large excess of free SG1, meaning that β‐hydrogen transfer from PMMA propagating radicals to the nitroxide SG1 was the major chain‐stopping event. On the other hand, for a low excess of free SG1, the two termination modes coexisted. Kinetic modeling was then performed using the PREDICI software, and the rate constant of β‐hydrogen transfer, k_βHtr, was estimated to be 1.69 × 10³ L mol^?1 s^?1 at 70 °C. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6333–6345, 2008     

Selective formation of diblock copolymers using radical trap‐assisted atom transfer radical coupling

Polystyrene (PSt) radicals and poly(methyl acrylate) (PMA) radicals, derived from their monobrominated precursors prepared by atom transfer radical polymerization (ATRP), were formed in the presence of the radical trap 2‐methyl‐2‐nitrosopropane (MNP), selectively forming PSt‐PMA diblock copolymers with an alkoxyamine at the junction between the block segments. This radical trap‐assisted, atom transfer radical coupling (RTA‐ATRC) was performed in a single pot at low temperature (35 °C), while analogous traditional ATRC reactions at this temperature, which lacked the radical trap, resulted in no observed coupling and the PStBr and PMABr precursors were simply recovered. Selective formation of the diblock under RTA‐ATRC conditions is consistent with the PStBr and PMABr having substantially different K_ATRP values, with PSt radicals initially being formed and trapped by the MNP and the PMA radicals being trapped by the in situ‐formed nitroxide end‐capped PSt. The midchain alkoxyamine functionality was confirmed by thermolysis of the diblock copolymer, resulting in recovery of the PSt segment and degradation of the PMA block at the relatively high temperatures (125 °C) required for thermal cleavage. A PSt‐PMA diblock formed by chain extenstion ATRP using PStBr as the macroinitiator (thus lacking the alkoxyamine between the PSt‐PMA segements) was inert to thermolysis. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 3619–3626     

Determination of the rate constants of recombination of macroradicals and stable radicals via the competitive-inhibition method

The rate constants of recombination, k _X, of propagating radicals with nitroxides in pseudoliving radical polymerization are determined via the competitive-inhibition method with the use of ESR spectroscopy. This method is applicable to determination of k _X in the reactions of propagating radicals of styrene, acrylic acid, and methyl methacrylate with two stable radicals, the nitroxide diethylphosphono-2,2-dimethylpropyl nitroxide and the phenoxide galvinoxyl. The values of k _X determined at 50°C increase in the following sequence: diethylphosphono-2,2-dimethylpropyl nitroxide-TEMPO-galvinoxyl. The selectivity of the low-activity propagating radicals of styrene in reactions with stable radicals is shown.     

Oxidation of quinolones with peracids (an in situ EPR study)

4‐Oxoquinoline derivatives (quinolones) represent heterocyclic compounds with a variety of biological activities, along with interesting chemical reactivity. The quinolone derivatives possessing secondary amino hydrogen at the nitrogen of the enaminone system are oxidized with 3‐chloroperbenzoic acid to nitroxide radicals in the primary step while maintaining their 4‐pyridone ring. Otherwise, N‐methyl substituted quinolones also form nitroxide radicals coupled with the opening of the 4‐pyridone ring in a gradual oxidation of the methyl group via the nitrone–nitroxide spin‐adduct cycle. This was confirmed in an analogous oxidation using N,N‐dimethylaniline as a model compound. N‐Ethyl quinolones in contrast to its N‐methyl analog form only one nitroxide radical without a further degradation. Copyright © 2013 John Wiley & Sons, Ltd.     

Influence of nitroxide structure on the 2,5‐ and 2,6‐spirodicyclohexyl substituted cyclic nitroxide‐mediated free‐radical polymerization of styrene

The 2,6‐spirodicyclohexyl substituted nitroxide, cyclohexane‐1‐spiro‐2′‐(3′,5′‐dioxo‐4′‐benzylpiperazine‐1′‐oxyl)‐6′‐spiro‐1″‐cyclohexane (BODAZ), was investigated as a mediator for controlled/living free‐radical polymerization of styrene. The values of the number‐average molecular weight increased linearly with conversion, but the polydispersities were higher than for the corresponding 2,2,6,6‐tetramethylpiperidinyl‐1‐oxy (TEMPO) and 2,5‐bis(spirocyclohexyl)‐3‐benzylimidazolidin‐4‐one‐1‐oxyl (NO88Bn) mediated systems at approximately 2.2 and 1.6 at 100 and 120 °C, respectively. These results were reflected in the rate coefficients obtained by electron spin resonance spectroscopy; at 120 °C, the values of the rate coefficients for polystyrene‐BODAZ alkoxyamine dissociation (k_d), combination of BODAZ and propagating radicals (k_c), and the equilibrium constant (K) were 1.60 × 10^?5 s^?1, 5.19 × 10⁶ M^?1 s^?1, and 3.08 × 10^?12 M, respectively. The value of k_d was approximately one and two orders of magnitude lower, and that of K was approximately 20 and 7 times lower than for the NO88Bn and TEMPO adducts. These results are explained in terms of X‐ray crystal structures of BODAZ and NO88Bn; the six‐membered ring of BODAZ deviates significantly from planarity as compared to the planar five‐membered ring of NO88Bn and possesses a benzyl substituent oriented away from the nitroxyl group leading to a seemingly more exposed oxyl group, which resulted in a higher k_c and a lower k_d than NO88Bn. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3892–3900, 2003     

A bidirectional ATRP‐NMRP initiator: The effect of nitroxide size on the rate of nitroxide‐mediated polymerization

An N‐alkoxyamine macroinitiator bearing a polymeric nitroxide cap was synthesized and used to investigate the effect of nitroxide size on the rate of nitroxide‐mediated radical polymerization (NMRP). This macroinitiator was prepared from asymmetric double‐headed initiator 9 , which contains both an α‐bromoester and an N‐alkoxyamine functionality. Poly(methyl methacrylate) was grown by atom transfer radical polymerization from the α‐bromoester end of this initiator, resulting in a macroinitiator (M_n = 31,000; PDI = 1.34) bearing a nitroxide cap permanently attached to a polymer chain. The polymerization kinetics of this macroinitiator in NMRP were compared with known N‐alkoxyamine initiator 1 . It was found that the rate of polymerization was unaffected by the size of the macromolecular nitroxide cap. It was confirmed that NMRP using this macroinitiator is a “living” process. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2015–2025, 2007