Polymers having stable radicals. II. Synthesis of nitroxyl polymers from 4-methacryloyl derivatives of 1-hydroxy-2,2,6,6-tetramethylpiperidine

Polymers having stable pendant . radicals were synthesized through their precursor polymers by oxidizing them in air or by H₂O₂–Na₂WO₄. Hydrochlorides and sulfates of 4-methacryloylamino- and 4-methacryloyloxy-1-hydroxy-2,2,6,6-tetramethylpiperidines were synthesized as precursor monomers and polymerized by using α,α′-azobisisobutyronitrile under appropriate conditions to precursor polymers of high molecular weight: poly-4-methacryloylamino-/oxy-1-hydroxy-2,2,6,6-tetramethylpiperidinehydrochlorides and sulfates. The precursor polymers were converted to polymers having nitroxyl stable radicals, i.e., poly-4-methacryloylamino-/oxy-2,2,6,6-tetramethylpiperidine-1-oxyls, by oxidation in air or with H₂O₂–Na₂WO₄ without any main-chain scission. The structure of the resultant stable radical polymers was determined by infrared, ultraviolet, and ESR spectroscopy. Based on the results of spectroscopic analysis and Kjeldahl analysis, the transformation from precursors to nitroxyl stable radical polymers was found to be quantitative. Investigations on the applicability of polymeric nitroxyl radicals to oxidation-reduction reactions were attempted by means of polarography; the reduction half-wave potential was found to be ?1.16 V for the mercury pool.     

Synthesis and polymerization of 4-o-vinylbenzyl-2,2,6,6-tetramethylpiperidine

Some hindered amine polymers containing 2,2,6,6-tetramethylpiperidine structure were synthesized. A new monomer, 4-O-vinylbenzyl-2,2,6,6-tetramethylpiperidine, was homopolymerized and copolymerized with some vinyl monomers in the presence of AIBN as an initiator. The obtained amine polymers were oxidized with hydrogen peroxide to obtain the polymers having nitroxyl radical moiety.     

“Living” free radical copolymerization of styrene and N-vinylcarbazole

Poly[styrene-co-(N-vinylcarbazole)] copolymers with controlled molecular weights and narrow polydispersities were synthesized by nitroxide-mediated “living” free radical copolymerization using an initiator/capping agent system consisting of benzoyl peroxide (BPO) and the stable nitroxyl radical 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO). The copolymerization behaves in a “living” fashion and allows the synthesis of poly[styrene-co-(N-vinylcarbazole)]/polystyrene block copolymers via a controlled chain-extension reaction of the prepared copolymers with styrene.     

Reactions of stabilizer compounds. IV. ESR studies of the formation of stable nitroxyl radicals in the photooxidation of polypropylene containing hindered amine light stabilizers

ESR studies of the formation of stable nitroxyl radicals in the photooxidation of polypropylene containing 2,2,6,6-tetramethyl-4-hydroxypiperidine (II) and the commercial light stabilizer bis(2,2,6,6-tetramethyl-4-piperidinyl)sebacate (III) are described. Spectra of the stable nitroxyl radicals in solid polymer and in solution after extraction from the polymer were obtained. The extract from photooxidized polypropylene containing the bifunctional stabilizer (III) showed only the mononitroxyl radical. The possible formation of polymer-bonded nitroxyl radicals from (III) is discussed.     

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     

Synthesis of AB2 miktoarm star-shaped copolymers by combining stable free radical polymerization and atom transfer radical polymerization

A stable nitroxyl radical functionalized with two initiating groups for atom transfer radical polymerization (ATRP), 4-(2,2-bis-(methyl 2-bromo isobutyrate)-propionyloxy)-2,2,6,6-tetramethyl-1-piperidinyloxy (Br₂-TEMPO), was synthesized by reacting 4-hydroxyl-2,2,6,6-tetramethyl-1-piperidinyloxy with 2,2-bis-(methyl 2-bromo isobutyrate) propanoic acid. Stable free radical polymerization of styrene was then carried out using a conventional thermal initiator, dibenzoyl peroxide, along with Br₂-TEMPO. The obtained polystyrene had two active bromine atoms for ATRP at the ω-end of the chain and was further used as the macroinitiator for ATRP of methyl acrylate and ethyl acrylate to prepare AB₂-type miktoarm star-shaped copolymers. The molecular weights of the resulting miktoarm star-shaped copolymers at different monomer conversions shifted to higher molecular weights without any trace of the macroinitiator, and increased with monomer conversion.     

Complex macromolecular structures from stable radical containing block copolymers

A novel synthetic strategy for the synthesis of graft copolymers is reported. Block copolymers containing segments with stable nitroxyl radicals side groups were first prepared by anionic polymerization, which were then used as a precursor for the subsequent nitroxide-mediated radical polymerization (NMRP) of styrene. This way, block–graft copolymers with polystyrene side chains grafted from one of the blocks were successfully synthesized in a controlled manner. In addition, block–graft copolymers with grafted polystyrene chains and a poly(tert-butyl methacrylate) block were subjected to hydrolysis to yield the corresponding amphiphilic polymers. The structures and the molecular weight characteristics of the polymers were characterized by spectral and chromatographic analyses. The surface morphology of thus obtained polymers was also investigated by microscopic techniques. © 2019 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 62–69     

TWO NEW METHODS OF ACTINOMETRY FOR EPR-MEASUREMENTS

Abstract— Two methods to perform actinometry in an EPR-cavity are described. One method is based on the observation that photoproduced anion radicals of hematoporphyrin react with the stable free radical 2,2,6,6-tetramethyl-4-piperidone-N-oxyl to eliminate the spin. The other method is based on the dye sensitized photoproduction of nitroxyl radicals resulting from the reaction of singlet oxygen with sterically hindered amines.     

Synthesis of Polystyrene‐block‐poly(butyl acrylate) Copolymers Using Nitroxide‐Mediated Living Radical Polymerization in Miniemulsion

Living free‐radical butyl acrylate polymerization in miniemulsion was initiated by polystyrene bearing a nitroxyl end group to yield polystyrene‐block‐poly(butyl acrylate) block copolymers. Polystyrene macroinitiator was obtained using different initiating systems (potassium persulfate or benzoyl peroxide) in the presence of 2,2,6,6‐tetramethylpiperidine‐N‐oxyl (TEMPO) or the more water‐soluble 4‐hydroxy‐2,2,6,6‐tetramethylpiperidin‐N‐oxyl (OH‐TEMPO). The nitroxide water‐solubility has an important influence in determining molecular weight distribution and controlling the growth of the second block.     

对二嗪N,N’-二氧化物光还原的电子自旋共振研究

报道了利用原位电子自旋共振(ESR)技术研究对二嗪N,N′-二氧化物光解的结果。研究结果表明,化合物5,6,7和8通过光还原过程从溶剂分子夺取氢原子分别生成稳定的自由基,记录出它们分辨良好的ESR谱。文中还讨论了对二嗪N,N′-二氧化物的光化学反应的自由基机理。     

Synthesis, photochemical stability and photo-stabilizing efficiency of probes based on benzothioxanthene chromophore and Hindered Amine Stabilizer

New types of combined chromophore-HAS (Hindered Amine Stabilizer) fluorescence probes were prepared and their photo-stability as well as their photo-stabilizing efficiency was tested in polypropylene film. The chromophore was benzothioxanthene and HAS was 2,2,6,6-tetramethylpiperidine. They were prepared by a one-step synthesis from benzothioxanthene-3,4-dicarboxylic anhydride (BTXA) by condensation with 4-amino-2,2,6,6-tetramethylpiperidine to obtain the probe in the form of parent amine (BTXI-NH) and 4-amino-1-oxy-2,2,6,6-tetramethylpiperidine in the case of stable nitroxyl radical form (BTXI-NO). Kinetics of BTXA photo-decomposition followed by UV spectroscopy were similar to kinetics of photo-decomposition for derivatives with covalently linked HAS i.e. BTXI-NH and BTXI-NO. It consists of two parts, slower in the beginning and very fast at the end of the process. Better stability of BTXI-NO in comparison with BTXI-NH can be explained by the presence of stable nitroxyl radical in its structure. The rate of decomposition of the fast part is similar for both additives. As soon as the decomposition starts there is no influence of NO or NH on this process. Times represented the start of the fast decomposition of probes correspond to the induction period of photo-oxidation of PP films. Possible effect of mutual interaction of chromophore and HAS coupled in one molecule (BTXI-NH or BTXI-NO) during photo-oxidation was followed by comparison with the course of photo-oxidation of PP film containing physical mixture of chromophore in the form of BTXA and HAS in the form of parent amine (4-hydroxy-2,2,6,6-tetramethylpiperidine) and stable nitroxyl radical (4-hydroxy-2,2,6,6-tetramethylpiperidin-N-oxyl).     

Synthesis and chemical structural analysis of nitroxyl‐radical‐incorporated poly(acrylic acid/lactide/ϵ‐caprolactone) copolymers

The goal of this research is to synthesize biodegradable polymers that would have nitroxyl radical biological functions. Linear aliphatic polyesters were chosen as the starting materials. The hydroxyl‐terminated polylactide/?‐caprolactones (PBLC‐OHs) were first synthesized by melt ring‐opening copolymerization in the presence of benzyl alcohol and stannous octoate. PBLC‐OHs were used as the precursor for the synthesis of double bond‐functionalized polylactide/?‐caprolactones (PBLC‐Mas) by reacting the hydroxyl end groups of PBLC‐OH with maleic anhydride in melt at 130 °C. Acrylic acid/lactide/?‐caprolactone graft copolymers (PBLCAs) were then successfully carried out by the radical copolymerization of acrylic acid and PBLC‐Ma initiated by azobisisobutyronitrile. Finally, nitroxyl radicals [4‐amino‐2,2,6,6‐tetramethylpiperidine‐1‐oxy (TAM)] were incorporated into the carboxylic acid sites of the acrylic acid/lactide/?‐caprolactone copolymer (TAM‐PBLCA) by reacting TAM with PBLCA in the presence of N,N′‐carbonyl diimidazole. A high content of TAM was incorporated into the PBLCA copolymer. The polymers synthesized were characterized by ¹H and ¹³C NMR, Fourier transform infrared spectroscopy, and electron paramagnetic resonance spectra. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 4214–4226, 2001     

Photostabilization of commercial polypropylene by hindered piperidine compounds: An ESR and luminescence study

The photostabilization of commercial polypropylene by a hindered piperidine stabilizer, bis [2,2,6,6-tetramethyl-4-piperidinyl] sebacate (I) and by a model N-oxy radical compound, 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxy (II) is examined using ESR and luminescence spectroscopy. ESR spectroscopy shows that I operates through the formation of a stable nitroxyl radical in the polymer. On the other hand, II disappears rapidly during the early stages of photo-oxidation but continues to act as an effective stabilizer. A low steady-state equilibrium concentration of nitroxyl radicals is believed to be responsible for the high photostabilizing efficiency of I. Both compounds also inhibit the photolysis of the luminescent α,β-unsaturated impurity groups present in the polymer; possible mechanisms are discussed.     

The Synthesis of New Type Diazo Compounds by 4-hydroxy-2,2,6,6-Tertramethyl-1-Piperidinyloxy 1 as The Phases Transfer Dehydrogenation Catalyst

It is well known that 4-hydroxy-2,2,6,6-tertramethyl-1-piperidinyloxyl is a stable nitroxyl radical. It can be used as antioxidants¹ and spin labeled compounds to mark protein, biomembrance and nucleic acid etc. Furthermore, as an efficient inhibitor, it can prevent olefin polymerizing by free radical. However, using 4-hydroxy-2,2,6,6-tertramethyl-1-piperidinyloxyl as the phase transfer catalyst has not been reported so far.     

Functional polymers. II. Synthesis and properties of new polymeric cinchona alkaloids

New polymeric cinchona alkaloids having favorable structures and properties for asymmetric catalysts have been prepared by radical copolymerization of the alkaloids with acrylonitrile using azobisisobutyronitrile (AIBN) as an initiator. Of the many reaction solvents tried, dimethylformamide (DMF) was found to be the solvent of choice especially for a large-scale synthesis. Alkaloid monomers employed were free dalkaloids, such as quinine, quinidine, cinchonidine, and cinchonine, and modified ones including 9-O-ethoxycarbonylquinine and quinine salts. The copolymers were thermally stable powders, soluble in DMF and DMSO, and insoluble in common organic solvents. They were found to be converted into water-soluble polymeric alkaloids by hydrolysis with alkaline hydrogen peroxide.     

Effect of polymer structure on ease of hydrogen abstraction by cumyloxy radicals

Vulcanizates of five elastomers having different chemical structures were prepared with recipes comprising dicumyl peroxide. Cumyl alcohol/acetophenone molar ratios were determined by gas–liquid chromatography (GLC) on acetone extracts of vulcanizates. Diphenyl ether was used as the internal standard. The ease of hydrogen abstraction by cumyloxy radicals, reflected by the cumyl alcohol/acetophenone ratio, decreases in the following order: cis-1,4-polyisoprene > poly(propylene oxide) > poly(vinyl n-butyl ether) > poly-1-heptene ? EPR. This order is in qualitative agreement with the order based on calculated relative rates of hydrogen abstraction by methyl and tert-butoxy radicals and literature data on oxygen absorption of some of these polymers as a result of hydrogen abstraction by peroxy radicals.     

Fractional free volumes in structural defects of butadiene–nitrile elastomers of various polarities and rotational mobilities of nitroxyl radicals

The correlation between the magnitudes of the fast components of rotational mobility of the nitroxyl radicals (2,2,6,6-tetramethylpiperidine-1-yl)oxyl and (4-benzoyloxy-2,2,6,6-tetramethylpiperidine-1-yl)oxyl measured via EPR spectroscopy, the fractional free volumes in the structural defects of butadiene–nitrile rubbers and the related vulcanized rubbers, in which the nitroxyl radicals are sorbed, and a variation in this correlation with an increase in temperature are established.     

Oxidation of benzyl alcohol with Fe(III) using polymers containing the nitroxyl radical structure as a mediator

Some polymers containing the nitroxyl radical structure were prepared and applied to the electron transfer agents from Fe(III) to benzyl alcohol. Benzyl alcohol was also oxidized by Fe(III) in two-phase or tri-phase systems using hydrophobic or hydrophilic polymers, which contain 2,2,6,6-tetramethylpiperidine-1-oxyl moiety, as an electron transfer catalyst. Especially, the hydrophilic polymers accelerated the oxidation of benzyl alcohol.     

Electrochemical modeling of the reaction of 1-Chloro- and 1-Bromo-2,2,6,6-tetramethylpiperidine photolysis

Electrolysis of 1-Chloro- and 1-Bromo-2,2,6,6-tetramethylpiperidines yields free nitroxyl radical 2,2,6,6-tetramethylpiperidine-1-oxyl. The reaction mechanism is suggested, which is based on the intermediate formation of aminyl radical. Concurrently with the nitroxyl radical formation, electrochemical chlorination of 2,2,6,6-tetramethylpiperidine occurs. It is shown that the 2,2,6,6-tetramethylpiperidine can be used as a mediator in the electrochemical oxidation of alcohols.     

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.