Polymerization of styrene and methyl methacrylate in the presence of 2,2-diethyl-4,5,5-trimethyl-2,5-dihydroimidazol-1-oxyl

The polymerization of styrene and methyl methacrylate in the presence of 2,2-diethyl-4,5,5-trimethyl- 2,5-dihydroimidazol-1-oxyl has been studied. It has been demonstrated that the nitroxyl radical makes it possible to control chain propagation in the polymerization of styrene and to synthesize polymers with relatively low polydispersity coefficients (<1.4). The polymerization of methyl methacrylate in the controlled mode cannot be performed because of the occurrence of a side reaction related to hydrogen atom transfer.     

Synthesis of block copolymers from polyvinyl chloride prepared in the presence of nitroxyl radicals of the imidazoline series

Specific features of radical polymerization of vinyl chloride in the presence of nitroxyl radicals of the imidazoline series (2-methyl-2,3-diphenyl-1,4-diazaspiro[4,5]dec-3-ene-1-oxyl, 2,2,5,5-tetramethyl-4-phenyl-2,5-dihydroimidazole-1-oxyl, 2,2,5-trimethyl-4,5-diphenyl-2,5-dihydroimidazole-1-oxyl) were studied. The possibility of preparing vinyl chloride-styrene block copolymers in the presence of these nitroxyl radicals was demonstrated, suggesting the occurrence of the polymerization by the reversible inhibition mechanism. The molecular-mass characteristics and the glass transition points of the synthesized samples were determined.     

Polymerization of styrene in the presence of nitroxide radicals of the dihydroimidazole series

2,2,5,5-Tetramethyl-4-phenyl-2,5-dihydroimidazole-1-oxyl and 2,2,5,5-tetramethyl-4-phenyl-2,5-dihydroimidazole-3-oxide-1-oxyl have been used as regulators of chain growth in the free-radical polymerization of styrene. It has been shown that the compounds of the dihydroimidazole series function as new living polymerization agents and allow the synthesis of polymers with low polydispersity coefficients and desired molecular masses.     

Synthesis of Poly （styrene-b-isoprene-b-styrene） via Nitroxide-mediated Radical Polymerization by a Novel Alkoxyamine

Bifunctional alkoxyamine bis-TIPNO derived from 2,2,5-trimethyl-4-phenyl-3-azahexane-3-oxyl （TIPNO） and α, ω-alkyl bromide by atom transfer radical addition（ATRA） was employed as “biradical initiator” for nitroxide-mediated radical polymerization（NMRP） of isoprene and styrene. The kinetics study for the polymerization of styrene at different time showed living features. The poly（styrene-b-isoprene-b-styrene） （SIS） copolymers have two glass transition temperatures, indicating the immiscibility of the corresponding blocks.     

Synthesis and polymerization of sterically hindered 2,5-diphenyl- and 2,3,5-triphenyl-1-vinylpyrroles

Sterically hindered 2,5-diphenyl-and 2,3,5-triphenyl-1-vinylpyrroles have been obtained by the vinylation of the corresponding NH-pyrroles with acetylene in superbasic catalytic system KOH—DMSO in up to 78% yield. 2,3,5-Triphenyl-1-vinylpyrrole has also been obtained in 75% yield by the regioselective bromination of 2,3-diphenyl-1-vinylpyrrole with subsequent cross-coupling of 5-bromo-2,3-diphenyl-1-vinylpyrrole with phenylmagnesium bromide in the presence of dichloro[1,1′-bis(diphenylphosphino)ferrocene]palladium(II). 2,5-Diphenyl- and 2,3,5-triphenyl-1-vinylpyrroles undergo a free-radical polymerization (AIBN, 80 °C) to form oligomers in 11 and 27% yield, respectively.     

A Proximal Bisnitroxide Initiator: Studies in Low-Temperature Nitroxide-Mediated Polymerizations

Nitroxide-mediated "living" radical polymerization with bisalkoxyamine 2,5,5,8,8,11-hexamethyl-4,9-(1-phenylethoxy)-3,10-diphenyl-4,9-diazadodecane produces polymers of controlled length and narrow molecular weight distributions at temperatures ranging from 70 to 110 °C. Polymerizations were run successfully with styrene (St), tert-butyl acrylate (tBA), and dimethylacrylamide (DMA). EPR measurements of the homolysis of this bisalkoxyamine and monoalkoxyamine 2,2,5-trimethyl-3-(1-phenylethoxy)-4-phenyl-3-azahexane at temperatures ranging from 85 to 105 °C give rate constants for the bisalkoxyamine that are approximately twice as large as those for the monoalkoxyamine. (1)H NMR investigations of the decomposition of both alkoxyamines at 125 °C show enhanced decomposition for the bisalkoxyamine. EPR decomposition studies at 120 °C on the corresponding bis- and mononitroxides 2,5,5,8,8,11-hexamethyl-3,10-diphenyl-4,9-diazadodecane-4,9-bisnitroxide and 2,2,5-trimethyl-4-phenyl-3-azahexane-3-nitroxide also show accelerated bisnitroxide decomposition. Low-temperature EPR studies of the bisnitroxide reveal an unusually strong radical-radical interaction, suggesting enhanced stabilization of the intermediate mononitroxide formed during polymerization by interaction with the proximal N-alkoxyamine. The transient mononitroxide is postulated to be stabilized by delocalization of the unpaired electron density over five atoms.     

Controlled radical polymerization of styrene in the presence of nitronyl nitroxides

Bulk radical polymerization of styrene in the presence of nitronyl nitroxides (2-(4-substituted phenyl)-4,4,5,5-tetramethyl-4,5-dihydroimidazolyl-1-oxyl 3-oxide) was studied. All nitronyl nitroxides, like other nitroxyl radicals such as 2,2,6,6-tetramethylpiperidine 1-oxyl radical (TEMPO), act as reversible radical scavengers. The efficiency of controlling the polymerization is affected by the substituent at the 4′-position. The efficiency increases with electron donating strength of 4′-substituents, at least at the beginning of the reaction. However, the thermal stability of nitronyl nitroxides decreases in the same order. Thus, TEMPO is more suitable than nitronyl nitroxides for controlled/“living” radical polymerization of styrene.     

Reaction of 3,4-diiodo-2,5-dimethyl-1H-pyrrole with thioamides

3,4-Diiodo-2,5-dimethyl-1H-pyrrole reacted with thioacetamide in polar solvents or under solvent-free conditions to give 2,4,6-trimethyl-5H-pyrrolo[3,4-d][1,3]thiazole. The major product in the reaction of the title compound with thiobenzamide was 3,5-diphenyl-1,2,4-thiadiazole.     

Synthesis and EPR investigation of nitroxyl derivatives of fullerenes C<Subscript>60</Subscript> and C<Subscript>70</Subscript>

Nitroxide derivatives of C₆₀ and C₇₀ were obtained by [3+2] cycloaddition of 4-(4-azidophenyl)-2,2,5,5-tetramethyl-3-oxy-2,5-dihydroimidazol-1-oxyl to fullerenes. The products were isolated by TLC and studied by EPR and optical spectroscopy. Molecular rotation of the adducts was shown to slow down on successive addition of the nitroxides, rotational correlation times depending nearly linearly on the number of the nitroxides added. Investigation of photochemical stability of nitroxide derivatives of C₆₀ and C₇₀ in benzene-ethanol medium reveal that the dissolved oxygen quenches efficiently the excitation of nitroxide (λ = 250–400 nm). In the absence of oxygen photoexcitation converts nitroxides to diamagnetic products, presumably, hydroxylamines formed through the interaction with the solvent.     

Gel permeation chromatographic determination of activation rate constants in nitroxide-controlled free radical polymerization, 2. Analysis of evolution of polydispersities

The dissociation rate constant k_d of the PS-TEMPO adduct, where PS is polystyrene and TEMPO is 2,2,6,6-tetramethylpiperidin-1-oxyl, was determined by the gel permeation chromatographic tracing of the evolution of polydispersities at an early stage of styrene polymerization with a model PS-TEMPO adduct as initiator. The results agree with those obtained by the direct method in Part 1.     

Living free radical donor-acceptor copolymerization of styrene and N-cyclohexylmaleimide and the synthesis of poly[styrene-co-(N-cyclohexylmaleimide)]/polystyrene block copolymers

Styrene/N-cyclohexylmaleimide copolymers with small polydispersities and controlled molecular weights were synthesized by a free radical copolymerization using an iniferter system consisting of benzoyl peroxide and 2,2,6,6-tetramethylpiperidine-N-oxyl. Due to the interactions of the electropositive (styrene) and electronegative (N-cyclohexylmaleimide) monomers the brutto polymerization rates are higher than for other living polymerizations initiated with the same iniferter system. The prepared copolymers were used as macroiniferters for bulk polymerization of styrene.     

基于2,5-二(4′-甲酰基苯基)苯乙烯的螺旋链光学活性聚合物的合成与表征

通过2,5-二溴苯乙烯与对甲酰基苯硼酸的Suzuki偶联反应得到2,5-二(4′-甲酰基苯基)苯乙烯.在催化剂量的冰乙酸存在下,与光学纯的(S)-(-)-α-甲基苄胺或(R)-(+)-α-甲基苄胺发生缩和反应,得到了一对手性非外消旋单体,(+)-2,5-二{4-′[(N-(S)-α-甲基苄亚胺基)次甲基]苯基}苯乙烯和(-)-2,5-二{4′-[(N-(R)-α-甲基苄亚胺基)次甲基]苯基}苯乙烯.以偶氮二异丁腈(AIBN)或过氧化苯甲酰(BPO)为引发剂,经自由基溶液聚合得到光学活性聚合物.比旋光度、紫外-可见吸收光谱以及圆二色光谱研究表明,聚合物主链可能形成了某一方向占优的稳定螺旋构象,且该螺旋构象的旋光方向与单体的旋光方向相反.聚合条件对聚合物的光学活性有很大影响,在极性较大的芳香族溶剂和较高温度下得到的聚合物具有和单体相差更大的比旋光度.侧基的手性基团脱除后,聚合物仍具有一定的旋光性,说明聚合过程中形成的螺旋手性具有一定的记忆效应.     

Synthesis and characterizations of novel spindle-like terphenyl-type chromophores for non-linear optical materials

A series of novel spindle-like terphenyl-type chromophores, based on 2,5-diphenyl-1,4-distyrylbenzene π-conjugating bridge, N,N-dimethyl and triphenyl amino donors, and Tricyanovinyldihydrofuran(TCF), 1,3,3-trimethyl-5-dicyanovinyl-1-cyclohexene (TDC) acceptors, have been synthesized successfully for the first time. And the non-linear optical properties were evaluated by using the finite-field (FF) method. The results show that, the first-order hyperpolarizability of the chromophores increase with the increase of the withdraw ability of the substituent group on the π-conjugating bridge.     

Role of the alkyl fragment of initiating alkoxyamine in nitroxide mediated polymerization of styrene

The role of the alkyl fragment of alkoxyamine initiating the homopolymerization of styrene is experimentally and theoretically studied in the case of 2,2,6,6-tetramethylpiperidine-1-oxyl derivatives. The rate constants of homolysis and recombination are measured for the alkoxyamines under study. The characteristics of polymerization initiated by these compounds are experimentally examined. The kinetics of polymerization is theoretically calculated with allowance for the measured kinetic parameters and the experimentally detected side reaction of hydrogen-atom transfer to the nitroxide radical during the thermolysis of alkoxyamine 2-cyano-2-isopropyl-TEMPO.     

Hydrodynamic characteristics of branched polystyrenes with varying content of a highly branched fraction

The branched polymers containing different amounts of the highly branched fraction are synthesized by the radical copolymerization of styrene and divinylbenzene under conditions of the reversible inhibition by 2,2,6,6-tetramethylpiperidine-1-oxyl. The branched polystyrenes are studied by size-exclusion chromatography combined with static light scattering, viscometry, and pulsed-field gradient nuclear magnetic resonance. The branched polymers prepared by living radical polymerization (in the presence of 2,2,6,6-tetramethylpiperidine-1-oxyl) feature reduced intrinsic viscosities and increased self-diffusion coefficients compared with their linear analogs. As the content of the highly branched fraction in the synthesized polymers grows, the Zimm contraction factor in toluene solution decreases to g′ = 0.13. The Kuhn-Mark-Houwink parameters for these polymers in toluene solution (a = 0.43) confirm the nonlinear architecture of macromolecules.     

Formation of unexpected products in the attempted aziridination of styrene with trifluoromethanesulfonyl nitrene

The reaction of styrene with trifluoromethanesulfonyl nitrene generated from trifluoromethanesulfonamide in the system (t-BuOCl+NaI) results in the formation of trifluoro-N-[2-phenyl-2-(trifluoromethylsulfonyl)aminoethyl]methanesulfonamide, 1-phenyl-2-iodo-ethanol, and 2,5-diphenyl-1,4-bis(trifluoromethylsulfonyl)piperazine rather than the expected product of aziridination, 2-phenyl-1-(trifluoromethylsulfonyl)aziridine. The mechanism of the reaction is discussed.     

Synthesis and structure of 3-(hydroxycarbamoyl)-2,2,5,5-tetramethyl-2,5-dihydropyrrol-1-oxyl

Hydroxyamination of 3-chlorocarbonyl-2,2,5,5-tetramethyl-2,5-dihydropyrrol-1-oxyl gave previously unknown 3-(hydroxycarbamoyl)-2,2,5,5-tetramethyl-2,5-dihydropyrrol-1-oxyl whose structure was determined by X-ray analysis. The hydroxamic acid fragment has cis configuration, and the carbonyl group occupies distorted trans position with respect to the double bond in the planar dihydropyrrole ring.     

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     

Some tetrazolium salts and their ion-association complexes with the molybdenum(VI) — 4-nitrocatechol anionic chelate

Several commercially available 2H-tetrazolium salts (TS) {2,3,5-triphenyl-2H-tetrazolium chloride (TTC), 3-(1-naphthyl)-2,5-diphenyl- 2H-tetrazolium chloride (Tetrazolium Violet, TV), 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl-2H-tetrazolium bromide (MTT), 2-(4-iodophenyl)-3-(4-nitrophenyl)-5-phenyl-2H-tetrazolium chloride (INT) and 3,3′-(3,3′-dimethoxy-4,4′-biphenylene)-bis(2,5-diphenyl- 2H-tetrazolium) chloride (Tetrazolium Blue Chloride, BTC)} and their ion-associated complexes (IAC) with the Mo(VI) — 4-nitrochatechol (4-NC) anionic chelate [MoO₂(4-NC)₂]²⁻ have been investigated by differential thermal analysis (DTA) and thermogravimetric analysis (TG). Some special features of the thermal behavior of the compounds have been discussed. The results show that the thermal stability of IAC depends on the factors determining the values of their association constants β: molecular mass and the presence of nitrophenyl substituent(s) in the tetrazolium ring.     

一种新型甲壳型液晶高分子的设计与合成

甲壳型液晶高分子是我国科学家最早设计和合成、受到国际学术界广泛关注的一类新型液晶高分子[1～ 6 ] .迄今已合成出 1 0个系列 1 0 0多种甲壳型液晶高分子 ,其中多数以乙烯基氢醌 [7] 、乙烯基对苯二胺 [8] 、乙烯基对苯二甲酸 [9] 和 2 -羟基 - 5-氨基苯乙烯 [10 ] 为关键中间体 .液晶核由 3个苯环以— COO—或— CONH—连接而成 .由于— COO—和— CONH—易与阳离子和阴离子相互作用 ,故已报道的甲壳型液晶高分子都是由自由基聚合反应制得 ,而很难用离子型聚合反应合成 .本文设计合成了一类未见文献报道的小分子液晶化合物 ,由此…