Synthesis of amphiphilic A2B star‐shaped copolymers of polystyrene‐b‐[poly(ethylene oxide)]2 via atom transfer nitroxide radical coupling

The amphiphilic A₂B star‐shaped copolymers of polystyrene‐b‐[poly(ethylene oxide)]₂ (PS‐b‐PEO₂) were synthesized via the combination of atom transfer nitroxide radical coupling (ATNRC) with ring‐opening polymerization (ROP) and atom transfer radical polymerization (ATRP) mechanisms. First, a novel V‐shaped 2,2,6,6‐tetramethylpiperidine‐1‐oxyl‐PEO₂ (TEMPO‐PEO₂) with a TEMPO group at middle chain was obtained by ROP of ethylene oxdie monomers using 4‐(2,3‐dihydroxypropoxy)‐TEMPO and diphenylmethyl potassium as coinitiator. Then, the linear PS with a bromine end group (PS‐Br) was obtained by ATRP of styrene monomers using ethyl 2‐bromoisobutyrate as initiator. Finally, the copolymers of PS‐b‐PEO₂ were obtained by ATNRC between the TEMPO and bromide groups on TEMPO‐PEO₂ and PS‐Br, respectively. The structures of target copolymers and their precursors were all well‐defined by gel permeation chromatographic and nuclear magnetic resonance (¹H NMR). © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Facile synthesis of polyester dendrimer via combining thio‐bromo “Click” chemistry and ATNRC

This article reports on developing an efficient synthesis approach to aliphatic polyester dendrimer, poly(thioglycerol‐2‐propionate) (PTP), by combination of thio‐bromo “Click” chemistry with atom transfer nitroxide radical coupling (ATNRC). Through the one‐pot two‐step method, linear polystyrene with hydroxyl end groups (l‐PS‐2OH) was obtained by first atom transfer radical polymerization of styrene and following termination using 4‐(2,3‐dihydroxypropoxy)‐TEMPO (DHP‐TEMPO) to capture the PS macroradicals via ATNRC method. Using l‐PS‐2OH as support, the dendritic repeating units divergently were grown from the hydroxyl end groups via esterification and thio‐bromo “Click” reaction two‐step process. In every generation, the resulting intermediates l‐PS‐d‐PTP (G1‐G4) can be easily isolated from the excessive unreacted monomers by simple precipitation in ethanol without help of time, labor and solvent consuming column chromatographic purification. At last, cleavage of the alkoxyamine group between the PS support and dendrimer at elevated temperature (125 °C) provided the targeted polyester dendrimer PTP up to the fourth generation. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1762–1768     

3‐miktoarm star terpolymers using triple click reactions: Diels–Alder,copper‐catalyzed azide‐alkyne cycloaddition,and nitroxide radical coupling reactions

Well‐defined linear furan‐protected maleimide‐terminated poly(ethylene glycol) (PEG‐MI), tetramethylpiperidine‐1‐oxyl‐terminated poly(ε‐caprolactone) (PCL‐TEMPO), and azide‐terminated polystyrene (PS‐N₃) or ‐poly(N‐butyl oxanorbornene imide) (PONB‐N₃) were ligated to an orthogonally functionalized core ( 1 ) in a two‐step reaction mode through triple click reactions. In a first step, Diels–Alder click reaction of PEG‐MI with 1 was performed in toluene at 110 °C for 24 h to afford α‐alkyne‐α‐bromide‐terminated PEG (PEG‐alkyne/Br). As a second step, this precursor was subsequently ligated with the PCL‐TEMPO and PS‐N₃ or PONB‐N₃ in N,N‐dimethylformamide at room temperature for 12 h catalyzed by Cu(0)/Cu(I) through copper‐catalyzed azide‐alkyne cycloaddition and nitroxide radical coupling click reactions, yield resulting ABC miktoarm star polymers in a one‐pot mode. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Star‐branched polystyrenes by nitroxide living free‐radical polymerization

Star‐branched polystyrenes, with polydispersity indices of 1.15–1.56 and 4–644 equal arms, were synthesized by the reaction of 2,2,6,6‐tetramethylpiperidin‐1‐yloxy (TEMPO)‐capped polystyrene (PS‐T) with divinylbenzene (DVB). The characterization of PS‐T and the final star polymers was carried out by size exclusion chromatography, low‐angle laser light scattering, and viscometry. The degree of branching of the star polymers depended on the DVB/PS‐T ratio and the PS‐T molecular weight. An asymmetric (or miktoarm) star homopolymer of the PS_nPS′_n type was made by the reaction of the PS_n symmetric star, which had n TEMPO molecules on its nucleus and consisted of a multifunctional initiator, with extra styrene. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 39: 320–325, 2001     

Synthesis of graft copolymers onto styrenic polymer backbone via “grafting from” raft process

A new synthetic methodology is developed for preparing graft copolymers via RAFT polymerization method by the “R group approach” onto styrenic polymers. In this approach, latent sites of the styrenic polymer was brominated first and then converted into macro‐RAFT agents with pyrazole and thio dodecyl as the Z groups. This was used to synthesize graft copolymer such as polystyrene‐graft‐polymethyl methacrylate (PS‐g‐PMMA), polystyrene‐graft‐poly(isobornyl acrylate), polystyrene‐graft‐poly[2‐(acetoacetoxy)ethyl methacrylate] (PS‐g‐PAEMA), and poly(para‐methoxystyrene)‐graft‐polystyrene (P(p‐MS)‐g‐PS). The polymers are characterized by gel permeation chromatography, ¹H NMR, IR, and atomic force microscopy (AFM). The morphology of PS‐g‐PMMA in THF was investigated using AFM and island‐like features were noticed. The AFM studies of the PS‐g‐PAEMA graft copolymers revealed the formation of globules and ribbon‐like morphological features. The PS‐g‐PAEMA graft copolymers form complex with Fe(III) in dimethylformamide and the AFM studies suggest the formation of globular superstructures. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

One‐pot preparation of ABA‐type block‐graft copolymers via a combination of “click” chemistry with atom transfer nitroxide radical coupling reaction

A new strategy for the one‐pot preparation of ABA‐type block‐graft copolymers via a combination of Cu‐catalyzed azide‐alkyne cycloaddition (CuAAC) “click” chemistry with atom transfer nitroxide radical coupling (ATNRC) reaction was reported. First, sequential ring‐opening polymerization of 4‐glycidyloxy‐2,2,6,6‐tetramethylpiperidine‐1‐oxyl (GTEMPO) and 1‐ethoxyethyl glycidyl ether provided a backbone with pendant TEMPO and ethoxyethyl‐protected hydroxyl groups, the hydroxyl groups could be recovered by hydrolysis and then esterified with 2‐bromoisobutyryl bromide, the bromide groups were converted into azide groups via treatment with NaN₃. Subsequently, bromine‐containing poly(tert‐butyl acrylate) (PtBA‐Br) was synthesized by atom transfer radical polymerization. Alkyne‐containing polystyrene (PS‐alkyne) was prepared by capping polystyryl‐lithium with ethylene oxide and subsequent modification by propargyl bromide. Finally, the CuAAC and ATNRC reaction proceeded simultaneously between backbone and PtBA‐Br, PS‐alkyne. The effects of catalyst systems on one‐pot reaction were discussed. The block‐graft copolymers and intermediates were characterized by size‐exclusion chromatography, ¹H NMR, and FT‐IR in detail. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

Filler effect on properties of “All‐Acrylic” copolymer/clay elastomeric materials synthesized by “in situ” nitroxide mediated polymerization

In this work, we describe the “in situ” synthesis of “all‐acrylic” copolymer (n‐butyl acrylate‐co‐methyl methacrylate)/clay materials at different low contents of raw and modified Montmorillonite (1–4 wt % versus monomer). The cationic 2,2′ azobis‐(amidinopropane)dihydrochloride initiator was used to modified the clay by cation exchange in combination with the N‐tert‐butyl‐N‐[1‐diethylphosphono‐(2,2‐dimethylpropyl)] (SG1) nitroxide to synthesize the polymer/clay nanocomposite via nitroxide mediated controlled radical polymerization. All synthesized materials are characterized by proton nuclear magnetic resonance, size exclusion chromatography, thermogravimetric analysis and differential scanning calorimetry techniques. The thermo‐mechanical properties of the synthesized materials are also reported. The results show that a decrease in molar masses and/or slight changes in molar compositions of poly (n‐butyl acrylate‐ co‐methyl methacrylate)/clay systems can be balanced by clay loading in polymer matrix, and consequently compensated or masked clay effects on physical properties of obtained materials. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Synthesis and characterization of amphiphilic heterograft copolymers with PAA and PS side chains via “Grafting from” approach

The amphiphilic heterograft copolymers poly(methyl methacrylate‐co‐2‐(2‐bromoisobutyryloxy)ethyl methacrylate)‐graft‐(poly(acrylic acid)/polystyrene) (P(MMA‐co‐BIEM)‐g‐(PAA/PS)) were synthesized successfully by the combination of single electron transfer‐living radical polymerization (SET‐LRP), single electron transfer‐nitroxide radical coupling (SET‐NRC), atom transfer radical polymerization (ATRP), and nitroxide‐mediated polymerization (NMP) via the “grafting from” approach. First, the linear polymer backbones poly(methyl methacrylate‐co‐2‐(2‐bromoisobutyryloxy)ethyl methacrylate) (P(MMA‐co‐BIEM)) were prepared by ATRP of methyl methacrylate (MMA) and 2‐hydroxyethyl methacrylate (HEMA) and subsequent esterification of the hydroxyl groups of the HEMA units with 2‐bromoisobutyryl bromide. Then the graft copolymers poly(methyl methacrylate‐co‐2‐(2‐bromoisobutyryloxy)ethyl methacrylate)‐graft‐poly(t‐butyl acrylate) (P(MMA‐co‐BIEM)‐g‐PtBA) were prepared by SET‐LRP of t‐butyl acrylate (tBA) at room temperature in the presence of 2,2,6,6‐tetramethylpiperidin‐1‐yloxyl (TEMPO), where the capping efficiency of TEMPO was so high that nearly every TEMPO trapped one polymer radicals formed by SET. Finally, the formed alkoxyamines via SET‐NRC in the main chain were used to initiate NMP of styrene and following selectively cleavage of t‐butyl esters of the PtBA side chains afforded the amphiphilic heterograft copolymers poly(methyl methacrylate‐co‐2‐(2‐bromoisobutyryloxy)ethyl methacrylate)‐graft‐(poly(t‐butyl acrylate)/polystyrene) (P(MMA‐co–BIEM)‐g‐(PtBA/PS)). The self‐assembly behaviors of the amphiphilic heterograft copolymers P(MMA‐co–BIEM)‐g‐(PAA/PS) in aqueous solution were investigated by AFM and DLS, and the results demonstrated that the morphologies of the formed micelles were dependent on the grafting density. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

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     

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     

SET‐LRP goes “green”: Various hemicellulose initiating systems under non‐inert conditions

Robust and versatile controlled radical polymerization, also in air, was achieved via single electron transfer living radical polymerization (SET‐LRP) initiated by purposely designed hemicellulose‐derived macroinitiators. The efficiency of the substitution reaction, converting the polysaccharides into bromo‐multifunctionalized initiators, as well as the rate of subsequent induced polymerizations of methyl acrylate were controlled by the hemicellulose repeating unit structure, branching pattern, and molecular weight. Macroinitiators with mannan‐based backbones induce SET‐LRP with somewhat higher apparent rate constants than xylan‐derived analogues, increasing by a factor two to three when raising the reaction temperature from 25 to 40 °C. The presence of lignin in a nonpurified xylan fraction did not impair its viability as a macroinitiator. Hemicellulose‐initiated SET‐LRP was feasible in air, proceeding with comparable or somewhat higher apparent rate constants than when conducted under deoxygenated conditions. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Influence of nitroxide structure on polystyrene brushes “grafted‐from” silicon wafers

Alkoxyamine derivatives based on 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO), N‐tert‐butyl‐N‐(1‐diethylphosphono‐(2,2‐dimethylpropyl)) nitroxide (SG1) and N‐tert‐butyl‐N‐(2‐methyl‐1‐phenylpropyl) nitroxide (TIPNO) containing a C₁₁ hydrophobic spacer and a reactive triethoxysilyl polar head, were synthesized and anchored to silicon wafers by the Langmuir–Blodgett reactive deposition technique at surface pressures ranging from 15 to 32 mN/m. Polystyrene brushes (M_n ～ 8500–66,400 g/mol) were grown from the alkoxyamine functionalized silicon wafers by nitroxide mediated radical polymerization and characterized by ellipsometry and water contact angle measurements. The main parameters influencing the grafting density and the degree of stretching of the brushes are the nitroxide polarity and, therefore, the behavior of the corresponding alkoxyamines at the air/water interface of the Langmuir–Blodgett trough. Depending on the alkoxyamine chemical structure and the surface pressure during Langmuir–Blodgett deposition, polystyrene brushes with grafting densities of 0.3–1.0 chains/nm² and stretching values of 40–70% were obtained. Regarding alkoxyamines deposited at high surface pressures, size exclusion chromatography experiments performed on both cleaved polystyrene brushes and chains simultaneously grown in the bulk revealed that the polymerization degree of the bulk and surface chains are significantly different, suggesting that steric constrains affect the polymerization kinetics occurring at the silicon surface. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3367–3374, 2008     

Mechanism and kinetics of the imidazolidinone nitroxide‐mediated free‐radical polymerization of styrene

Styrene radical polymerizations mediated by the imidazolidinone nitroxides 2,5‐bis(spirocyclohexyl)‐3‐methylimidazolidin‐4‐one‐1‐oxyl (NO88Me) and 2,5‐bis(spirocyclohexyl)‐3‐benzylimidazolidin‐4‐one‐1‐oxyl (NO88Bn) were investigated. Polymeric alkoxyamine (PS‐NO88Bn)‐initiated systems exhibited controlled/living characteristics at 100–120 °C but not at 80 °C. All systems exhibited rates of polymerization similar to those of thermal polymerization, with the exception of the PS‐NO88Bn system at 80 °C, which polymerized twice as quickly. The dissociation rate constants (k_d) for the PS‐NO88Me and PS‐NO88Bn coupling products were determined by electron spin resonance at 50–100 °C. The equilibrium constants were estimated to be 9.01 × 10^?11 and 6.47 × 10^?11 mol L^?1 at 120 °C for NO88Me and NO88Bn, respectively, resulting in the combination rate constants (k_c) 2.77 × 10⁶ (NO88Me) and 2.07 × 10⁶ L mol^?1 s^?1 (NO88Bn). The similar polymerization results and kinetic parameters for NO88Me and NO88Bn indicated the absence of any 3‐N‐transannular effect by the benzyl substituent relative to the methyl substituent. The values of k_d and k_c were 4–8 and 25–33 times lower, respectively, than the reported values for PS‐TEMPO at 120 °C, indicating that the 2,5‐spirodicyclohexyl rings have a more profound effect on the combination reaction rather than the dissociation reaction. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 327–334, 2003     

TEMPO‐mediated dispersion polymerization of styrene in the presence of camphorsulfonic acid

The TEMPO‐mediated polymerization of styrene in the presence of camphorsulfonic acid (CSA) is carried out using controlled radical dispersion polymerization. In the absence of TEMPO and CSA, 92% of conversion was achieved within 3 h of polymerization. When TEMPO is solely used, broadening of particle size with narrow PDI was observed because of the prolonged polymerization time. However, when 1:1 molar ratio of CSA/TEMPO was added, the fairly monodisperse PS microspheres having 5.83 μm average size and 3.42% C_V (coefficient of variation) were successfully achieved because of the narrow molecular weight of intermediate oligomers and shortening of the polymerization time. This result obviously indicates that the addition of CSA in TEMPO‐mediated dispersion polymerization not only shortens the polymerization time but also greatly improves the uniformity of the microspheres. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 62–68, 2006     

Copper(0)‐catalyzed one‐pot synthesis of ABC triblock copolymers via the combination of single electron transfer nitroxide radical coupling reaction and “click” chemistry

The synthesis of ABC triblock copolymers were accomplished by Cu(0)‐catalyzed one‐pot strategy combining single electron transfer‐nitroxide radical coupling (SET‐NRC) reaction with “click” chemistry. First, the precursors α,ω‐heterofunctionalized poly(ethylene oxide) (PEO) with a 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO) group and an alkyne group, polystyrene (PS), and poly(tert‐butyl acrylate) (PtBA) with bromine or azide end group were designed and synthesized, respectively. Then, the one‐pot coupling reactions between these precursors were carried out in the system of Cu(0)/Me₆TREN: The SET‐NRC reaction between bromine group and nitroxide radical group, subsequently click coupling between azide and alkyne group. It was noticeable that Cu(I) generated from Cu(0) by SET mechanism was utilized to catalyze click chemistry. To estimate the effect of Cu(0) on the one‐pot reaction, a comparative analysis was performed in presence of different Cu(0) species. The result showed that Cu(0) with more active surface area could accelerate the one‐pot reaction significantly. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Preparation of star block copolymers with polystyrene‐block‐poly(ethylene oxide) as side chains on hyperbranched polyglycerol core by combination of ATRP with atom transfer nitroxide radical coupling reaction

The star block copolymers with polystyrene‐block‐poly(ethylene oxide) (PS‐b‐PEO) as side chains and hyperbranched polyglycerol (HPG) as core were synthesized by combination of atom transfer radical polymerization (ATRP) with the “atom transfer nitroxide radical coupling” (“ATNRC”) reaction. The multiarm PS with bromide end groups originated from the HPG core (HPG‐g‐(PS‐Br)_n) was synthesized by ATRP first, and the heterofunctional PEO with α‐2,2,6,6‐tetramethylpiperidinyl‐1‐oxy group and ω‐hydroxyl group (TEMPO‐PEO) was prepared by anionic polymerization separately using 4‐hydroxyl‐2,2,6,6‐tetramethylpiperidinyl‐1‐oxy (HTEMPO) as parents compound. Then ATNRC reaction was conducted between the TEMPO groups in PEO and bromide groups in HPG‐g‐(PS‐Br)_n in the presence of CuBr and pentamethyldiethylenetriamine (PMDETA). The obtained star block copolymers and intermediates were characterized by gel permeation chromatography, nuclear magnetic resonance spectroscopy, fourier transform‐infrared in detail. Those results showed that the efficiency of ATNRC in the preparation of multiarm star polymers was satisfactory (>90%) even if the density of coupling cites on HPG was high. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6754–6761, 2008     

Preparation of comb‐like copolymers with amphiphilic poly(ethylene oxide)‐b‐polystyrene graft chains by combination of “graft from” and “graft onto” strategies

A novel method for preparation the comb‐like copolymers with amphihilic poly(ethylene oxide)‐block‐poly(styrene) (PEO‐b‐PS) graft chains by “graft from” and “graft onto” strategies were reported. The ring‐opening copolymerization of ethylene oxide (EO) and ethoxyethyl glycidyl ether (EEGE) was carried out first using α‐methoxyl‐ω‐hydroxyl‐poly(ethylene oxide) (mPEO) and diphenylmethyl potassium (DPMK) as coinitiation system, then the EEGE units on resulting linear copolymer mPEO‐b‐Poly(EO‐co‐EEGE) were hydrolyzed and the recovered hydroxyl groups were reacted with 2‐bromoisobutyryl bromide. The obtained macroinitiator mPEO‐b‐Poly(EO‐co‐BiBGE) can initiate the polymerization of styrene by ATRP via the “Graft from” strategy, and the comb‐like copolymers mPEO‐b‐[Poly(EO‐co‐Gly)‐g‐PS] were obtained. Afterwards, the TEMPO‐PEO was prepared by ring‐opening polymerization (ROP) of EO initiated by 4‐hydroxyl‐2,2,6,6‐tetramethyl piperdinyl‐oxy (HTEMPO) and DPMK, and then coupled with mPEO‐b‐[Poly(EO‐co‐Gly)‐g‐PS] by atom transfer nitroxide radical coupling reaction in the presence of cuprous bromide (CuBr)/N,N,N′,N″,N″‐pentamethyldiethylenetriamine (PMDETA) via “Graft onto” method. The comb‐like block copolymers mPEO‐b‐[Poly(EO‐co‐Gly)‐g‐(PS‐b‐PEO)] were obtained with high efficiency (≥90%). The final product and intermediates were characterized in detail. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1930–1938, 2009     

Decomposition of model alkoxyamines in simple and polymerizing systems. II. Diastereomeric N‐(2‐methylpropyl)‐N‐(1‐diethyl‐phosphono‐2,2‐dimethyl‐propyl)‐aminoxyl‐based compounds

Thermal reactions of the alkoxyamine diastereomers DEPN‐R′ [DEPN: N‐(2‐methylpropyl)‐N‐(1‐diethylphosphophono‐2,2‐dimethyl‐propyl)‐aminoxyl; R′: methoxy‐carbonylethyl and phenylethyl] with (R,R) + (S,S) and (R,S) + (S,R) configurations have been investigated by ¹H NMR at 100 °C. During the overall decay the diastereomers interconvert, and an analytical treatment of the combined processes is presented. Rate constants are obtained for the cleavage and reformation of DEPN‐R′ from NMR, electron spin resonance, and chemically induced dynamic nuclear polarization experiments also using 2,2,6,6‐tetramethylpiperidinyl‐1‐oxyl (TEMPO) as a radical scavenger. The rate constants depend on the diastereomer configuration and the residues R′. Simulations of the kinetics observed with styrene and methyl methacrylate containing solutions yielded rate constants for unimeric and polymeric alkoxyamines DEPN‐(M)_n‐R′. The results were compatible with the known DEPN mediation of living styrene and acrylate polymerizations. For methyl methacrylate the equilibrium constant of the reversible cleavage of the dormant chains DEPN‐(M)_n‐R′ is very large and renders successful living polymerizations unlikely. Mechanistic and kinetic differences of DEPN‐ and TEMPO‐mediated polymerizations are discussed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3264–3283, 2002     

Preparation of main‐chain imidazolium‐functionalized amphiphilic block copolymers through combination of condensation polymerization and nitroxide‐mediated free radical polymerization and their micelle study

Main‐chain imidazolium‐functionalized amphiphilic block copolymers (PIL‐b‐PS) consisting of polyionic liquid (PIL) and polystyrene (PS) blocks have been first synthesized by condensation polymerization combined with nitroxide‐mediated free radical polymerization (NMP). The di‐functional imidazolium‐based ionic liquid (IL) having both hydroxyl and ester end groups was synthesized through Michael addition between imidazole and methylacrylate (MA) and further quaternization by 2‐chloroethanol. The HTEMPO (4‐hydroxy‐2,2,6,6‐tetramethyl‐1‐piperidinyloxy) terminated polyionic liquid (HTEMPO‐PIL) as the hydrophilic block was prepared by condensation polymerization of di‐functional imidazolium IL and HTEMPO at a certain ratio. The hydrophobic PS block was synthesized by controlled radical polymerization of styrene using HTEMPO‐PIL through NMP, resulting PIL‐b‐PS block copolymers. The structure of block copolymers obtained has been characterized and verified by FTIR, ¹H NMR, and size exclusion chromatography analyses. In addition, the morphology and size of the micelles formed by PIL‐b‐PS block copolymers in water were investigated by transmission electron microscopy and dynamic light scattering. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

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