A versatile approach for the preparation of end‐functional polymers and block copolymers by stable radical exchange reactions

A versatile strategy for the preparation of end‐functional polymers and block copolymers by radical exchange reactions is described. For this purpose, first polystyrene with 2,2,6,6‐tetramethylpiperidine‐1‐oxyl end group (PS‐TEMPO) is prepared by nitroxide‐mediated radical polymerization (NMRP). In the subsequent step, these polymers are heated to 130 °C in the presence of independently prepared TEMPO derivatives bearing hydroxyl, azide and carboxylic acid functionalities, and polymers such as poly(ethylene glycol) (TEMPO‐PEG) and poly(ε‐caprolactone) (TEMPO‐PCL). Due to the simultaneous radical generation and reversible termination of the polymer radical, TEMPO moiety on polystyrene is replaced to form the corresponding end‐functional polymers and block copolymers. The intermediates and final polymers are characterized by ¹H NMR, UV, IR, and GPC measurements. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2387–2395     

Nitroxide mediated living radical polymerization of styrene onto poly (vinyl chloride)

Nitroxide‐mediated ‘living’ free radical polymerisation (LREP) was employed for the first time to prepare graft copolymer by having arylated poly (vinyl chloride) (PVC‐Ph) as a backbone and polystyrene (PS) as branches. The graft copolymerization of styrene was initiated by arylated PVC carrying 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO) groups as a macroinitiator. Thus, the arylated PVC was prepared in the mild conditions and these reaction conditions could overcome the problem of gelation and crosslinking in polymers. Then, 1‐hydroxy TEMPO was synthesized by the reduction of TEMPO with sodium ascorbate. This functional nitroxyl compound was coupled with brominated arylated PVC (PVC‐Ph‐Br). The resulting macro‐initiator (PVC‐Ph‐TEMPO) for ‘living’ free radical polymerization was then heated in the presence of styrene to form graft copolymer. DSC, GPC, ¹HNMR, and FT‐IR spectroscopy were employed to investigate the structure of the polymers. Copyright © 2007 John Wiley & Sons, Ltd.     

Polymerization of o‐quinodimethanes. IV. Radical polymerization of 1‐cyano‐o‐quinodimethane in the presence of TEMPO

The radical polymerization behavior of 1‐cyano‐o‐quinodimethane generated by thermal isomerization of 1‐cyanobenzocyclobutene in the presence of 2,2,6,6‐tetramethylpiperidine‐N‐oxide (TEMPO) and the block copolymerization of the obtained polymer with styrene are described. The radical polymerization of 1‐cyanobenzocyclobutene was carried out in a sealed tube at temperatures ranging from 100 to 150 °C for 24 h in the presence of di‐tert‐butyl peroxide (DTBP) as a radical initiator and two equivalents of TEMPO as a trapping agent of the propagation end radical to obtain hexane‐insoluble polymer above 130 °C. Polymerization at 150 °C with 5 mol % of DTBP in the presence of TEMPO resulted in the polymer having a number‐average molecular weight (M_n ) of 2900 in 63% yield. The structure of the obtained polymer was confirmed as the ring‐opened polymer having a TEMPO unit at the terminal end by ¹H NMR, ¹³C NMR, and IR analyses. Then, block copolymerization of the obtained polymer with styrene was carried out at 140 °C for 72 h to give the corresponding block copolymer in 82% yield, in which the unimodal GPC curve was shifted to a higher molecular weight region. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3434–3439, 2000     

Controlled free radical ring-opening polymerization and chain extension of the “living” polymer

Free radical ring-opening polymerization of 2-methylene-1,3-dioxepane (MDP) in the presence of 2,2,6,6-tetramethyl-1-piperidinyloxy free radical (TEMPO) has been achieved to afford a chain polyester (PMDP) with di-t-butyl peroxide (DTBP) as an initiator at 125°C. The polydispersity of the polymers decreases as the concentration of TEMPO is increased. At high TEMPO concentrations, the polydispersity as low as 1.2 was obtained, which is below the theoretical lower limit for a conventional free radical polymerization. A linear relationship between the number-average molecular weight (M_n) and the monomer conversion was observed with the best-fit line passing very close to the origin of the M_n-conversion plot. The isolated and purified TEMPO-capped PMDP polymers have been employed to prepare chain extended polymers upon addition of more MDP monomer. These results are suggestive of the “living” polymerization process. A possible polymerization mechanism might involve thermal homolysis of the TEMPO-PMDP bonds followed by the addition of the monomers. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 761–771, 1998     

Synthesis of well‐defined multigraft copolymers by a two‐step living radical polymerization with nitroxyl‐functionalized poly(methyl methacrylate)

Novel multigraft copolymers of poly(methyl methacrylate‐graft‐polystyrene) (PMMA‐g‐PS) in which the number of graft PS side chains was varied were prepared by a subsequent two‐step living radical copolymerization approach. A polymerizable 4‐vinylbezenyl 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO) monomer (STEMPO), which functioned as both a monomer and a radical trapper, was placed in a low‐temperature atom transfer radical polymerization (60°C) process of methyl methacrylate with ethyl 2‐bromopronionate (EPNBr) as an initiator to gain ethyl pronionate‐capped prepolymers with TEMPO moieties, PMMA‐STEMPOs. The number of TEMPO moieties grafted on the PMMA backbone could be designed by varying STEMPO/EPNBr, for example, the ratios of 1/2, 2/3, or 3/4 gained one, two, or three graft TEMPO moieties, respectively. The resulting prepolymers either as a macromolecular initiator or a trapper copolymerized with styrene in the control of stable free‐radical polymerization at an elevated temperature (120 °C), producing the corresponding multigraft copolymers, PMMA‐g‐PSs. The nitroxyl‐functionalized PMMA prepolymers produced a relatively high initiation efficiency (>0.8) as a result of the stereohindrance and slow diffusion of TEMPO moieties connected on the long PMMA backbone. The polymerization kinetics in two processes showed a living radical polymerization characteristic. The molecular structures of these prepolymers and graft copolymers were well characterized by combining Fourier transform infrared spectroscopy, gel permeation chromatography, chemical element analysis, and ¹H NMR. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1876–1884, 2002     

Deactivation reactions in the modeled 2,2,6,6‐tetramethyl‐1‐piperidinyloxy‐mediated free‐radical polymerization of styrene: A comparative study with the 2,2,6,6‐tetramethyl‐1‐piperidinyloxy/acrylonitrile system

The competitiveness of the combination and disproportionation reactions between a 1‐phenylpropyl radical, standing for a growing polystyryl macroradical, and a 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO) radical in the nitroxide‐mediated free‐radical polymerization of styrene was quantitatively evaluated by the study of the transition geometry and the potential energy profiles for the competing reactions with the use of quantum‐mechanical calculations at the density functional theory (DFT) UB3‐LYP/6‐311+G(3df, 2p)//(unrestricted) Austin Model 1 level of theory. The search for transition geometries resulted in six and two transition structures for the radical combination and disproportionation reactions, respectively. The former transition structures, mainly differing in the out‐of‐plane angle of the N? O bond in the transition structure TEMPO molecule, were correlated with the activation energy, which was determined to be in the range of 8.4–19.4 kcal mol^?1 from a single‐point calculation at the DFT UB3‐LYP/6‐311+G(3df, 2p)//unrestricted Austin Model 1 level. The calculated activation energy for the disproportionation reaction was less favorable by a value of more than 30 kcal mol^?1 in comparison with that for the combination reaction. The approximate barrier difference for the TEMPO addition and disproportionation reaction was slightly smaller for the styrene polymerization system than for the acrylonitrile polymerization system, thus indicating that a β‐proton abstraction through a TEMPO radical from the polymer backbone could diminish control over the radical polymerization of styrene with the nitroxide even more than in the latter system. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 232–241, 2007     

Synthesis of poly(styrene-b-tetrahydrofuran-b-styrene) triblock copolymers by transformation from living cationic into living radical polymerization using 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl as a transforming agent

Synthesis of poly(styrene-b-tetrahydrofuran (THF)-b-styrene) triblock copolymers was performed by transformation from living cationic into living radical polymerization, using 4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl (4-hydroxy-TEMPO) as a transforming agent. Sodium 4-oxy-TEMPO, derived from 4-hydroxy-TEMPO, reacted with the living poly(THF), which was prepared by cationic polymerization of THF using trifluoromethanesulfonic acid anhydride as an initiator, resulting in quantitative formation of the poly(THF) with TEMPO at both the chain ends. The resulting polymers were able to serve as a polymeric counter radical for the radical polymerization of styrene by benzoyl peroxide, to give the corresponding triblock copolymer in quantitative efficiency. The polymerization was found to proceed in accordance with a living mechanism, because the conversion of styrene linearly increased over time, and the molar ratio of styrene to THF units in the copolymer also increased as a result of increasing the conversion. The TEM pictures demonstrated that the resulting copolymers promoted microphase segregation. It was found that the films of these copolymers showed contact angles intermediate between those of poly(THF) and of polystyrene. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 2059–2068, 1998     

Porphyrin derivatives act as vinylene monomers in TEMPO‐mediated radical copolymerization with styrene

In this article, we offer clear evidence for the radical copolymerizability of porphyrin rings in 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO)‐mediated radical copolymerizations with styrene. The radical copolymerizations of styrene with 5,10,15,20‐tetrakis(pentafluorophenyl)porphyrin (H₂TFPP) was conducted using 1‐phenyl‐1‐(2,2,6,6‐tetramethyl‐1‐piperidinyloxy)ethane as an initiator. The refractive index (RI) traces for the size‐exclusion chromatography of the resulting copolymers were unimodal with narrow molecular weight distributions. The RI traces shifted toward higher molecular weight regions as the polymerization progressed, and the number‐average molecular weights were close to those calculated on the basis of the feed compositions and monomer conversions. These features were in good agreement with a TEMPO‐mediated mechanism. The traces recorded by the ultraviolet‐visible (UV‐vis) detector (430 nm) were identical to those obtained by the RI detector, indicating a statistical copolymerization of styrene with H₂TFPP. This also indicated that H₂TFPP acted as a monomer and not as a terminator or a chain‐transfer agent under the conditions used. A benzyl radical addition to H₂TFPP was conducted as a model reaction for the copolymerization using tributyltin hydride as a chain‐transfer agent, affording a reduced porphyrin, 2‐benzyl‐5,10,15,20‐tetrakis(pentafluorophenyl)chlorin 1 , via radical addition to the β‐pyrrole position. The UV‐vis spectrum of 1 was fairly similar to that of poly(styrene‐co‐H₂TFPP), indicating that H₂TFPP polymerized at its β‐pyrrole position in the TEMPO‐mediated radical polymerization. TEMPO‐mediated radical copolymerizations of styrene with several porphyrin derivatives were also demonstrated. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Controlled free‐radical polymerization of 2‐vinylpyridine in the presence of nitroxides

Bulk free‐radical polymerization of 2‐vinylpyridine (2VP) in the presence of 2,2,6,6‐tetramethylpiperidine‐N‐oxyl (TEMPO) was studied under different conditions (temperature and presence of additives). Linear poly‐(2‐vinylpyridine) with a narrow molecular weight distribution and controllable molecular weight was prepared in the presence of acetic anhydride at 95 °C up to a conversion of 66%. At higher conversions side reactions became very important (pseudoliving polymerization). By applying this procedure, well‐defined random copolymers of 2VP with styrene or tert‐butylmethacrylate as well as block copolymers of 2VP with styrene were synthesized. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 2889–2895, 2001     

Investigation of nitroxide radical coupling reaction in wide temperature range and different catalyst system

The effect of temperature, catalyst system, and the structure of bromine connected groups on the nitroxide radical coupling (NRC) reaction is investigated in details. A series of polymers with different bromine connected groups as poly (tert‐butyl acrylate) (PtBA‐Br), polystyrene (PS‐Br), and poly (methyl methacrylate) (PMMA‐Br) are prepared by atom transfer radical polymerization first, then the bromine‐containing polymers were coupled with 2,2,6,6‐tetramethylpiperidinyl‐1‐oxy‐containing poly(ε‐caprolactone) (PCL‐TEMPO) in different catalyst systems as CuBr/PMDETA, Cu⁰/PMDETA and CuBr/Cu⁰/PMDETA in the temperature range from 90 °C to 25 °C. The result shows that the catalyst system of CuBr/Cu⁰/PMDETA is the best one for NRC reaction, in which the NRC reaction could be conducted in high efficiency in the wide temperature range from room temperature to high temperature. The efficiency of NRC reaction between PtBA‐Br and PCL‐TEMPO is more than 85% in the temperature range from 25 to 75 °C, the efficiency between PS‐Br and PCL‐TEMPO is more than 90% from 25 to 90 °C, and the efficiency between PMMA‐Br and PCL‐TEMPO is more than 90% only at the room temperature. The effect of bromine connected groups on the NRC reaction is discussed. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2991–2999, 2010     

Low temperature TEMPO‐mediated styrene polymerization in miniemulsion

The 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO)‐mediated stable free radical polymerization of styrene in miniemulsion at 100 °C is demonstrated. Although this temperature is 20–35 °C lower than typical temperatures used for TEMPO‐mediated polymerizations, reasonable reaction rates were achieved by the addition of ascorbic acid or a free radical initiator. More importantly, the living character of the chains was preserved; the degree of polymer “livingness” was comparable to polymerizations conducted at 135 °C. Polydispersities were broader than that observed in well‐controlled systems, ranging from ～1.4–1.6, and consistent with expectations for systems having a low activation rate. The results are significant for two reasons. They will facilitate TEMPO‐mediated minemulsion polymerizations in nonpressurized (or minimally pressurized) reactors, and they reveal the potential to expand the traditional temperature range of TEMPO and possibly other nitroxides in bulk, solution, and miniemulsion. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 232–242, 2006     

Oxoaminium salts as initiators for cationic polymerization of vinyl monomers

Oxoaminium salt ( 1 ), derived from 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO, 2 ) by one-electron oxidation, could be an initiator for cationic polymerization of vinyl monomers such as isobutyl vinyl ether (IBVE), 2,3-dihydrofuran, p-methoxystyrene, N-vinyl pyrrolidone, etc., to give the corresponding polymers, when 1 had a low nucleophilic counter anion. Formation of the adducts of 1 and IBVE as well as ¹H-NMR and IR data suggested the formation of polymers containing N? O? C structure as the polymer head group. In the polymerization of IBVE, the effects of solvent and concentration of 1 were little observed, however the polymerization rate was dependent on temperature. Furthermore, the thermal reaction of the polymers obtained, which were regarded as prepolymers for block copolymerization and polymeric initiators for radical polymerization, was studied. For example, poly(2-benzylidene-1,3-dioxane) obtained by the polymerization of 2-benzylidene-1,3-dioxane with oxoaminium hexafluoroantimonate ( 1, X = SbF₆) was employed as an initiator for radical polymerization of MMA to give its block copolymer with PMMA. © 1993 John Wiley & Sons, Inc.     

Polymerization of styrene with tetramethylthiuram disulfide as an initiator in the presence of 2,2,6,6‐tetramethyl‐1‐piperidinyloxy

The bulk polymerization of styrene was investigated with tetramethylthiuram disulfide (TMTD) as an initiator in the presence of 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO) at 123 °C. The polymerization proceeded in a controlled/living way; that is, the polymerization rate was first‐order with respect to the monomer concentration, and the molecular weight increased linearly with conversion. The molecular weights of the polymers obtained were close to the theoretical values, and the molecular weight distributions were relatively low (weight‐average molecular weight/number‐average molecular weight = 1.1–1.3). The rate of polymerization with TMTD as an initiator was faster than that with benzoyl peroxide, and the rate was independent of the initial concentration of TMTD in the presence of TEMPO. The obtained polystyrene was functionalized with ultraviolet‐light‐sensitive ? SC(S)N(CH₃)₂ groups, which was characterized with ¹H NMR spectroscopy. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 543–551, 2005     

Nitroxide partitioning between styrene and water

Research into nitroxide‐mediated radical polymerization (NMRP) performed in emulsions and miniemulsions has progressed significantly over the past several years. However, our knowledge of the conditions during polymerization (e.g., the nitroxide concentrations in the aqueous and organic phases) is incomplete, and as such we have yet to achieve a clear understanding of the mechanisms involved in these processes. To better understand the conditions present in heterogeneous NMRP, we measured the partition coefficients of 2,2,6,6‐tetramethylpiperidinyl‐1‐oxy (TEMPO), 4‐hydroxy‐TEMPO, and 4‐amino‐TEMPO between styrene and water from 25 to 135 °C. Experiments were performed in a 250‐mL Parr reactor that was equipped for the simultaneous sampling of the aqueous and organic phases. Aqueous‐phase and organic‐phase nitroxide concentrations were measured with ultraviolet–visible spectrophotometry. Experiments were also performed at 135 °C in the presence of hexadecane (costabilizer), polystyrene, and sodium dodecylbenzenesulfonate (surfactant) to determine the effects of the miniemulsion polymerization recipe ingredients on the partitioning of TEMPO and 4‐hydroxy‐TEMPO. On the basis of the measured partition coefficients (expressed as the ratio of the nitroxide concentration in the organic phase to the nitroxide concentration in the aqueous phase), 4‐hydroxy‐TEMPO was the most hydrophilic of the nitroxides investigated, followed by 4‐amino‐TEMPO and TEMPO. Hexadecane, polystyrene, and sodium dodecylbenzenesulfonate did not have a significant influence on the partitioning of these nitroxides at 135 °C. Experiments with ethylbenzene instead of styrene demonstrated that thermally generated radicals were not responsible for the observed temperature effects on the measured partition coefficients. © 2001 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 1081–1089, 2001     

Thermal self‐initiation of styrene in the presence of TEMPO radicals: Bulk and miniemulsion

In TEMPO (2,2,6,6,‐tetramethyl‐1‐piperidinyloxy) controlled styrene radical polymerizations, the thermal self‐initiation reaction of styrene monomer is one of the main sources for the deviations from ideal living polymerization. However, it is also important because it continuously generates radicals to compensate for the loss of radicals caused by the termination reactions and thereby maintains a reasonable reaction rate. In this report, different initial TEMPO concentrations were used in styrene miniemulsion polymerizations without any added initiator. The consumption rate of TEMPO or radical generation rate was calculated from the length of the induction period and the increasing total number of polymer chains. It was found that there is little difference between the miniemulsions and the corresponding bulk systems in terms of the length of the induction period, which increases linearly with initial TEMPO concentration. After the induction period, the consumption rate of TEMPO or radical generation rate was reduced to a lower level, and a faster initial polymerization rate was found in the bulk system compared to the corresponding miniemulsion system. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4921–4932, 2004     

Some aspects of nitroxide-mediated living radical polymerization of N-(p-vinylbenzyl)phthalimide

The free radical polymerization of N-(p-vinylbenzyl)phthalimide (VBP) “initiated” with the adduct of 2-benzoyloxy-1-phenylethyl and TEMPO (BS-TEMPO) or TEMPO-terminated polystyrene (PS-TEMPO) in N,N-dimethylformamide (DMF) at 125 °C was found to proceed in a living fashion, providing low-polydispersity PVBP and block copolymers of the type PS-b-PVBA, where TEMPO is 2,2,6,6-tetramethylpiperidinyl-1-oxy. Unlike TEMPO-mediated styrene polymerization, the polymerization rate slightly but distinctly depended on the adduct concentration, which was interpretable as a pre-stationary behavior. The hydrolysis of those polymers gave poly(p-aminomethylstyrene) (PAMS) and PS-b-PAMS, and further treatment of the block copolymer with hydrogen chloride provided an amphiphilic block copolymer. The polymeric amphiphile was used as an emulsifier in emulsion polymerization to produce a positively charged polymeric microsphere.     

Polymer grafting onto carbon black by use of TEMPO-terminated polystyrene with controlled molecular weight

The grafting of polystyrene with controlled molecular weight and narrow molecular weight distribution onto the carbon black surface through the trapping of polymer radicals formed by the thermal dissociation of 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO)-terminated polystyrene (PSt-TEMPO) by the carbon black surface was investigated. PSt-TEMPO was prepared by living radical polymerization of St with the benzoyl peroxide/TEMPO system. When PSt having no terminal TEMPO moiety was heated with carbon black, no grafting of PSt onto the surface was observed. On the contrary, by the heating of PSt-TEMPO with carbon black in m-xylene at 125°C, PSt with controlled molecular weight and narrow molecular weight distribution was grafted onto the surface: the percentage grafting of PSt (M_n = 3.2 × 10³;M_w/M_n = 1.07) onto furnace black was determined to be 16.0%. On the basis of the above results, it is concluded that PSt radicals formed by the thermal dissociation of the C ON bond between PSt and TEMPO are trapped by polycondensed aromatic rings of carbon black. The mole number of grafted PSt chains on the carbon black surface decreased with increasing molecular weight of PSt-TEMPO. PSt-grafted carbon black gave a stable colloidal dispersion in THF. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 3165–3172, 1998     

Acrylonitrile‐containing polymers via a combination of metal‐catalyzed living radical and nitroxide‐mediated free‐radical polymerization routes

2‐Phenyl‐2‐[(2,2,6,6‐tetramethylpiperidino)oxy] ethyl 2‐bromopropanoate was successfully used as an initiator in consecutive living radical polymerization routes, such as metal‐catalyzed living radical polymerization and nitroxide‐mediated free‐radical polymerization, to produce various types of acrylonitrile‐containing polymers, such as styrene–acrylonitrile, polystyrene‐b‐styrene–acrylonitrile, polystyrene‐b‐poly(n‐butyl acrylate)‐b‐polyacrylonitrile, and polystyrene‐b‐polyacrylonitrile. The kinetic data were obtained for the metal‐catalyzed living radical polymerization of styrene–acrylonitrile. All the obtained polymers were characterized with ¹H NMR, gel permeation chromatography, and differential scanning calorimetry. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3374–3381, 2006     

Decomposition of model alkoxyamines in simple and polymerizing systems. I. 2,2,6,6‐tetramethylpiperidinyl‐ N‐oxyl‐based compounds

The thermal decomposition of five alkoxyamines labeled TEMPO–R, where TEMPO was 2,2,6,6‐tetramethylpiperidinyl‐N‐oxyl and R was cumyl (Cum), 2‐tert‐butoxy‐carbonyl‐2‐propyl (PEst), phenylethyl (PhEt), 1‐tert‐butoxy‐carbonylethyl (EEst), or 1‐methoxycarbonyl‐3‐methyl‐3‐phenylbutyl (Acrylate‐Cum), was studied with ¹H NMR in the absence and presence of styrene and methyl methacrylate. The major products were alkenes and the hydroxylamine 1‐hydroxy‐2,2,6,6‐tetramethyl‐ piperidine (TEMPOH), and in monomer‐containing solutions, unimeric and polymeric alkoxyamines and alkenes were also found. Furthermore, the reactions between TEMPO and the radicals EEst and PEst were studied with chemically induced dynamic nuclear polarization. In comparison with coupling, TEMPO reacted with the radicals Cum, PEst, PhEt, and EEst and their unimeric styrene adducts by disproportionation to alkenes and TEMPOH only to a minor extent (0.6–3%) but with the radical adducts to methyl methacrylate to a considerable degree (≥20%). Parallel to the radical cleavage, TEMPO–EEst (but not the other alkoxyamines or TEMPO–Acrylate‐Cum) underwent substantial nonradical decay. The consequences for TEMPO‐mediated living radical polymerizations are discussed. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3604–3621, 2001     

Synthesis of diblock copolymers by combining stable free radical polymerization and atom transfer radical polymerization

A stable nitroxyl radical functionalized with an initiating group for atom transfer radical polymerization (ATRP), 4‐(2‐bromo‐2‐methylpropionyloxy)‐2,2,6,6‐tetramethyl‐1‐piperidinyloxy (Br‐TEMPO), was synthesized by the reaction of 4‐hydroxyl‐2,2,6,6‐tetramethyl‐1‐piperidinyloxy with 2‐bromo‐2‐methylpropionyl bromide. Stable free radical polymerization of styrene was then carried out using a conventional thermal initiator, dibenzoyl peroxide, along with Br‐TEMPO. The obtained polystyrene had an active bromine atom for ATRP at the ω‐end of the chain and was used as the macroinitiator for ATRP of methyl acrylate and ethyl acrylate to prepare block copolymers. The molecular weights of the resulting block copolymers at different monomer conversions shifted to higher molecular weights and increased with monomer conversion. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2468–2475, 2006