Influence of N-oxyls on the free radical autopolymerization of styrene

Through comparative studies on the controlled thermally initiated radical polymerization of styrene in the presence of N-oxyls, the effect of the type of the N-oxyls (2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO), 4-hydroxy-2,2,6,6-tetramethylpiperidine-N-oxyl (OH-TEMPO), 4-oxo-2,2,6,6-tetramethylpiperidine-N-oxyl (oxo-TEMPO) and 4-acetamido-2,2,6,6-tetramethylpiperidine-N-oxyl (acetamido-TEMPO)), as well as the concentration of the N-oxyls (3–20 mmol L^–1) are discussed. The radical formation proceeds exclusively through the thermal initiation of styrene, i.e. without using any initiator. It is observed, that the thermal self-initiation of styrene increases the radical yield remarkably with the N-oxyls concentration, independent of the type of the N-oxyl. The concentration-dependent side reactions of substituted N-oxyls are remarkably more pronounced than those of unsubstituted N-oxyl. This leads to the reduction of the overall rate of polymerization (v_br) as compared to TEMPO (v_br = v_br (thermal polymerization)) with respect to the concentration, but independent of the type of substituents.     

TEMPO／BPO引发苯乙烯聚合反应的研究

由三丙酮胺经改进的Ｗｏｌｆ－Ｋｉｓｈｎｅｒ还原反应首先合成了２,２,６,６－四甲基哌啶,再参照Ｒｏｚａｎｔｚｅｖ报道的方法将２,２,６,６－四甲基哌啶氧化制备了２,２,６,６－四甲基哌啶－１－氧稳定氮氧自由基（ＴＥＭＰＯ）,研究了ＴＥＭＰＯ的存在对过氧化苯甲酰引发苯乙聚合反应的影响,分子量分布指数（ＭＷ／Ｍｎ）为１．１９－１．３５的窄分散的聚苯乙烯。     

Synthesizing and characterization of comb-shaped carbazole containing copolymer via combination of ring opening polymerization and nitroxide-mediated polymerization

The macro-TEMPO agent (poly(4-glycidyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl), PGTEMPO) was synthesized by anion ring-opening polymerization (ROP) of 4-glycidyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl (GTEMPO) using potassium t-butoxide as the initiator. The comb-shaped copolymer, PGTEMPO-g-PVBK, was prepared via nitroxide-mediated free radical polymerization (NMP) using PGTEMPO as macro-TEMPO agent and 9-(4-vinylbenzyl)-9H-carbazole (VBK) as the monomer. The polymerizations showed characteristics of “living”/controlled behavior. The optical properties, thermal analysis and electrochemical properties of the comb-shaped copolymers were investigated. The fluorescence and ultraviolet intensity and cyclic voltammetries of the comb-shaped copolymers with different molecular weight showed a regular order.     

Nitroxide‐mediated radical polymerization of 4‐vinylpyridine and its application on modification of silicon substrate

The poly(4‐vinylpyridine) with hydroxyl end group and narrow polydispersity was synthesized by polymerization of 4‐vinylpyridine by the use of nitroxide initiator based on 4‐hydroxy‐2,2,6,6‐tetramethylpiperidin‐1‐oxyl and azobisisobutyronitrile. The effects of different initiator amounts and reaction time on polymerization rate, molecular weight, and molecular weight distribution of the poly(4‐vinylpyridine) were investigated at bulk polymerization. The experimental results have shown that the polymerization of 4‐vinylpyridine is a controlled living free‐radical polymerization; the molecular weight is proportional to reaction time; and the molecular weight and molecular weight distribution are affected by molar ratios of [4‐hydroxy‐2,2,6,6‐tetramethylpiperidin‐1‐oxyl]/[azobisisobutyronitrile]. By varying the ratio of 4‐hydroxy‐2,2,6,6‐tetramethylpiperidin‐1‐oxyl to azobisisobutyronitrile, the poly(4‐vinylpyridine) with narrow polydispersity can be obtained. X‐ray photoelectron spectroscopy results show that the synthesized poly(4‐vinylpyridine) can be tethered on the surface of silicon wafer through the reaction between hydroxyl end of poly(4‐vinylpyridine) and native silicon oxide layer on the wafer surface. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 2687–2692, 2002     

Synthesis and reactivity of functionalized alkoxyamine initiators for nitroxide‐mediated radical polymerization of styrene

The synthesis and examination of different functionalized (2,2,6,6‐tetramethyl‐1‐piperidinyloxy free radical) TEMPO‐containing alkoxyamine initiators for nitroxide‐mediated radical polymerization of styrene are reported. Initiators with ester and carbonate functional groups were synthesized by a low‐temperature radical‐abstraction reaction of the functionalized ethylbenzene in the presence of TEMPO to introduce the functional groups onto the initiating chain‐end of polystyrene. An initiator with two alkoxyamine groups symmetrically located at each end of a carbonate bond was also synthesized and used for nitroxide‐mediated styrene polymerization. Styrene polymerization using these initiators followed first‐order kinetics up to approximately 60 min at 140 °C or 30% monomer conversion. Alkoxyamines bearing an acetoxy or tert‐butylcarbonate group at the p‐position of 1‐(2,2,6,6‐tetramethyl‐1‐piperidinyloxy)ethylbenzene behave in a similar way to the unfunctionalized initiator. With an initiator containing two alkoxyamine groups, the resulting polymer molecular weight was twice that of the polymer obtained from initiators with only one alkoxyamine group, as expected from propagation from both chain‐ends. Upon hydrolysis of the carbonate bond, it was revealed that equivalent polymer chain growth occurred from each alkoxyamine site in the difunctional initiator. Copyright © 2003 Society of Chemical Industry     

First report of nitroxide mediated polymerization in an ionic liquid

Summary Nitroxide-mediated free radical polymerizations (NMP) of styrene (St) and methyl methacrylate (MMA) were carried out in a room temperature ionic liquid: 1-butyl-3-methylimidazolium hexafluorophosphate ([bmim]PF₆). A bimolecular initiation system, benzoyl peroxide (BPO) along with 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) and a unimolecular initiation system, 2,2,5-trimethyl-3-(1-phenylethoxy)-4-phenyl-3-azahexane (-hydrido alkoxyamine, TMPPAH)) were employed. Contrary to the results obtained for atom transfer radical polymerization (ATW) and reversible addition-fragmentation radical transfer polymerization (RAFT) in the same ionic liquid, the molecular weights obtained in NMP were lower with broader polydispersities for a wide range of initiator ratios and temperatures due to the non-living nature of polymerization.     

Kinetics studies on the free radical polymerization of styrene in the presence of asphalts

A study was made of the free radical polymerization of styrene in bulk at 60°C initiated with 2,2′-azoisobutyronitrile in the presence of the stable free radical 4-hydroxy-2,2,6,6-tetramethyl-piperidine-1-oxyl (TMHPO) and two types of petroleum asphalts D and F. It was found that petroleum asphalts contain compounds effective as polymerization inhibitors and that they also include substances taking part in initiation processes. The differences between the kinetics behaviour of asphalts in comparison with stable free radicals were the subject of the discussion.     

Stable free radical polymerization of styrene with 4-sulphonate-2,2,6,6-tetramethylpiperidine-N-oxyl as mediators

The stable free radical polymerizations of styrene were investigated with five 4-sulphonate-2,2,6,6-tetramethylpiperidine-N-oxyl stable radicals as mediators and benzoyl peroxide (BPO) as initiators at 125 °C. The results indicated that the polymerizations proceeded in a “living”/controlled manner, i.e., the polymerization rates were first-order with respect to the monomer concentrations, molecular weights increased linearly with conversions and the molecular weight distributions were relatively low (M _w/M _n = 1.2–1.4), ¹H NMR analysis of the polymer chain-ends and successful chain extensions. The polymerization rates were faster than that of 4-hydroxyl-2,2,6,6-tetramethylpiperidine-N-oxyl (OH-TEMPO) mediated ones. The effects of steric interference of different substitute groups at four-position of 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO), the molar ratios of stable radical to BPO and the temperature on the polymerizations were investigated.     

Synthesis and characterization of N-phenylmaleimide-methylvinylisocyanate copolymers with polystyrene side chains

Summary N-Substitued maleimide-methylvinylisocyanate copolymers with high glass transition temperature (T_g) was prepared and reacted with 4-hydroxy TEMPO (4-hydroxy-2,2,6,6-tetramethyl piperidinoxy) to yield polymers possessing stable radical at the side chain. The resulting polymers behaved as polymeric counter radicals for the radical polymerization of styrene. Thus, stable free radical mediated polymerization at the side chain was achieved. The resulting graft copolymers were characterized by spectral and thermal analysis. Received: 6 October 1999/Revised version: 7 March 2000/Accepted: 7 March 2000     

Chemical modification of polypropylene by nitroxide-mediated radical graft polymerization of styrene

Nitroxide-mediated free radical polymerization (LREP) was employed for the first time to prepare graft copolymer by having arylated polypropylene (Cl-PP) as a backbone and polystyrene (PS) as branches. The graft copolymerization of styrene was initiated by arylated PP carrying 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) groups as a macroinitiator. Thus, maleic anhydride was grafted onto polypropylene by peroxide-catalyzed swell grafting method (PP-MAH). Next, PP-MAH reacted with ethanolamine to produce a hydroxyl group containing polypropylene (PP-OH) and the obtained PP-OH was treated with α-phenyl chloroacetyl chloride and converted to a chloroacetyl group containing polypropylene (PP-Cl). Finally, 1-hydroxyl-2,2,6,6-tetramethylpiperidine (TEMPO-OH) was synthesized by reducing TEMPO with sodium ascorbate and this functional nitroxyl compound was coupled with α-phenyl chloroacetylated polypropylene. The resulting macroinitiator (PP-TEMPO) for free radical polymerization was then heated in the presence of styrene for the formation of the graft copolymer. The prepared graft copolymer was characterized by Fourier transform infrared spectroscopy and ¹H NMR techniques. Glass transition temperature of grafted copolymer was investigated using thermogravimetric analysis and differential scanning calorimetric techniques. This approach using nitroxide-mediated macroinitiators is an effective method for the preparation of new materials.     

High conversion study of “living” radical polymerization of styrene using DSC

The influence of temperature on nitroxide-controlled living radical polymerization of styrene was examined. It has been established that only in a temperature range of 110°C to 150°C nitroxides are able to control radical polymerization. At temperatures above 160°C the reaction was of rather a free radical character. The results were similar for all the various nitroxides used as capping agents: TEMPO (2,2,6,6-tetramethylpiperidine-N-oxyl), 4-hydroxy-TEMPO, 4-oxo-TEMPO and 4-acetamido-TEMPO. Differences were found only in the induction times of polymerization and were probably due to side reactions with the initiator (benzoyl peroxide). Living radical polymerization can be best controlled with these nitroxides at temperatures between 120°C and 140°C.     

Novel thione-thiol rearrangement of dithiocarbonic acid O-(2,2,6,6-tetramethylpiperidin-1-yl) ester in the context of controlled radical polymerization

Addition of the lithium salt of N-hydroxy-2,2,6,6-tetramethylpiperidine 10 to carbon disulfide and subsequent methylation affords the rearranged dithiocarbonic acid S-methyl-S'-(2,2,6,6-tetramethylpiperidin-1-yl)-ester 9 rather than the expected xanthate ester S-methyl-O'-(2,2,6,6-tetramethylpiperidin-1 -yl)-ester 8. n-Butylacrylate could be polymerized with the novel compound 9 even though the polymerization was not controlled.     

Thermal polymerization of styrene in the presence of TEMPO

To investigate aspects of the contribution of (thermal) self-initiation in nitroxide-mediated radical polymerization (NMRP) of styrene, selective styrene polymerizations with 2,2,6,6-tetramethyl-1-piperidinyloxy (TEMPO) in the absence of initiator were carried out at 120 and 130 °C. The results of these experiments (including conversion data, molecular weight averages, polydispersity and molecular weight distribution information) were compared with regular thermal polymerization of styrene and NMRP of styrene in the presence of a bimolecular initiator (benzoyl peroxide; BPO). It was observed that although the thermal polymerization of styrene can be controlled to some extent in the presence of TEMPO to provide polystyrene with low polydispersity, the polymerization was never as controlled as that obtained by a BPO-initiated NMRP.     

A Convenient Method for Preparation of Amphiphilic Monomethoxypoly (Ethylene Glycol)–Polystyrene Diblock Copolymer by NMRP Technique

Amphiphilic block copolymers are macromolecular compounds of great importance from both fundamental scientific and many technological point of views for a large variety of applications. Amphiphilic diblock copolymer containing segments of monomethoxypoly(ethylene glycol) and polystyrene (MPEG-b-PS) was synthesised by a convenient method for preparation of macroinitiator MPEG-TEMPO for ‘living’ free radical polymerization (NMRP technique). Initially, derivative of MPEG with chlorine function has been prepared in an one-step reaction with thionyl chloride. 1-hydroxy-2,2,6,6-tetramethyl-piperidine (TEMPO-OH) obtained by reduction of 2,2,6,6-tetramethyl-piperidinyl-1-oxy (TEMPO) with sodium ascorbate was coupled with chlorinated MPEG to yield the macroinitiator MPEG terminated with a TEMPO unit (MPEG-TEMPO), which was further used to prepare the diblock copolymer MPEG-b-PS of styrene. The product was purified and identified by ¹H NMR, GPC and, FT-IR.     

Studium der lebenden radikalischen Polymerisation mit der Differential Scanning Calorimetry (DSC)

The living radical polymerization of styrene, some styrene-analogous vinyl monomers as well as methyl methacrylate (MMA) and butyl methacrylate (BuMA) was investigated with a differential scanning calorimeter. The ability to polymerize was estimated by dynamic measurements, showing that p-methylstyrene, p-chlorostyrene, 3,4-dimethoxystyrene and 4-vinylpyridine polymerize in the presence of 2,2,6,6-tetramethyl-1-piperidine-N-oxyl (TEMPO) while MMA and BuMA do not. Isothermal measurements revealed an activation energy of E_A = 81 kJ mol^–1 for thermal bulk polymerization of styrene and values of E_A = 78–94 kJ mol^–1 were measured with different iniferter systems. These polymerizations have induction times which depend on the reaction temperature and the initial concentration of the iniferter systems. An influence of the kind of nitroxyl radical on the induction times was not observed.     

New dinitroxide for stable free radical polymerization of styrene

A new dinitroxide (1,4‐di (1‐oxy‐2,2,6,6‐tetramethyl‐1‐piperidin‐4‐yl)‐xylene) (DTPX) was synthesized and successfully used in stable free radical polymerization of styrene. The results of the polymerizations showed that the DTPX was a suitable mediating agent for stable free radical polymerization of styrene. However, it was found that the dinitroxide mediating process resulted in a higher level of decomposition of the internal bisalkoxyamine linkage in the polymer chain, which resulted in polymers possessing a terminal alkoxyamine and an adjacent hydroxylamine, and the decomposition became more obvious at high conversion through monitoring the change of molecular weights with the conversion by gel permeation chromatography and the polymer structure by ¹H‐NMR. The reaction temperature showed obvious effects on the polymerization, and the polymerization of styrene at 110°C led to a better controlled polymerization than that at 125°C with narrower molecular weight distributions and slight decomposition of the nitroxide up to monomer conversions of 76.7%, however, the rate of the polymerization was decreased and an induction period appeared at 110°C. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1137–1145,2006     

Polyallene with pendant nitroxyl radicals

A new polyradical containing polyallene backbone and stable pendant nitroxyl radicals was synthesized using 4-hydroxyl-2,2,6,6-tetramethylpiperidine as starting material. Firstly, a new allenyl ether monomer, 4-allenyloxyl-2,2,6,6-tetramethyl piperidine was prepared by 2 steps. Next, BPO initiated the traditional free radical polymerization of 4-allenyloxyl-2,2,6,6-tetramethyl piperidine at 100 °C to obtain the homopolymer, poly(4-allenyloxyl-2,2,6,6-tetramethyl piperidine). Finally, the homopolymer was quantitatively oxidized by H₂O₂/Na₂WO₄·2H₂O/EDTA at room temperature to yield the final product, poly(4-allenyloxyl-2,2,6,6-tetramethyl piperidine-1-oxyl). Studies on the electrochemical properties of polyradical showed excellent charging/discharging reversibility and stability with a high columbic efficiency of 98%, which suggested that the synthesized polyradical is a promising cathode material for lithium secondary battery.     

Controlled radical polymerization

Summary The free radical polymerization of chloromethylstyrene (CMS) with benzoyl peroxide (BPO) as initiator and 2,2,6,6 tetramethyl-1-piperidiniloxy (Tempo) as counter radical was studied. The living character was demonstrated by the linear dependence of versus conversion like that the control with polydispersity lower than 1,5. In a second step, styrene was introduced in polychloromethylstyrene capped with Tempo to produce PCMS-b-PS block copolymers (12,000/60,000) with and PCMS-Tempo macroinitiator efficiency closed to 85%.     

Rate enhancement of the N-oxyl-controlled free radical copolymerization of styrene with N-vinylcarbazole

Poly(styrene-co-N-vinylcarbazole) copolymers with controlled molecular weights and narrow polydispersities were synthesized by N-oxyl-controlled free radical copolymerization using benzoyl peroxide as initiator and 2,2,6,6-tetramethylpiperidine-N-oxyl as terminating agent. To improve the low polymerization rates, the radical initiator dicumyl peroxide (DCP) was introduced and its effects on the polymerization rate, the molecular weight and the polydispersity were studied. It was demonstrated that the introduction of DCP leads to a significant enhancement of the polymerization rate and that copolymers with high N-vinylcarbazole contents as well as N-vinylcarbazole homopolymer can be obtained. The enhancement of the polymerization rate corresponds to a decrease in the number of chain breaking reactions which leads to polymers with lower polydispersities compared with those polymerized at the same monomer conversion without DCP. This could be proved via comparative chain-extension experiments with styrene leading to poly(styrene-co-N-vinylcarbazole)-block-poly(styrene) diblock copolymers.     

A replicated investigation of nitroxide‐mediated radical polymerization of styrene over a range of reaction conditions

A comprehensive experimental investigation of nitroxide‐mediated radical polymerization (NMRP) of styrene using 2,2,6,6‐tetramethyl‐1‐piperidinyloxy (TEMPO) as controller is presented. Polymerizations with a bimolecular initiator (benzoyl peroxide; BPO) were carried out at 120 and 130°C, with TEMPO/BPO molar ratios ranging from 0.9 to 1.5. Results indicate that increasing temperature increases the rate of polymerization while the decrease in molecular weights is only slight. It was also observed that increasing the ratio of TEMPO/BPO decreased both the rate of polymerization and molecular weights. Probably for the first time in the history of such investigations, the paper contains a comprehensive database, appropriate for parameter estimation in aid of future modelling studies, since it comes from a systematic data collection containing independent replication.