有机过氧化物与N,N-二羟烷基对甲苯胺引发体系的研究

<正> 有机过氧化二苯甲酰(BPO)与N,N-二甲基苯胺(DMA)组成的引发体系称为有机氧化还原引发体系.为了提高聚合速度和聚合物的颜色稳定性,发展了BPO-DMT(N,N-二甲基对甲苯胺)引发体系,并已应用于医用高分子的齿科材料和骨水泥中.文献[3]曾简单提到N,N-二2-羟乙基苯胺(DHEA)作为促进剂,其活性与DMA相似;另外BPO可分别与N,N-二(2-羟乙基)对甲苯胺(DHET)和N,N-二(2-羟丙基)对甲苯胺(DHPT)组成引发体系,作为烯类自由基聚合的室温固化剂,但对聚合速度和聚合动力学报道甚少.由于DHPT熔点较高又无刺激味道,因而很适用于自凝齿科林     

芴酮-甲基丙烯酸N,N-二甲氨基乙酯引发丙烯腈光聚合的研究

二苯酮(BP)-脂肪叔胺体系作为光氧化还原引发体系引发烯类单体的光聚合已有许多研究。甲基丙烯酸N,N-二甲氨基乙酯(DMAEM)是含有脂肪叔胺基的丙烯酸酯类。由于含有叔胺基,它不仅能参与和芳香酮类构成的光氧化还原引发体系,其本身还参与聚合反应。 三川等报道了DMAEM在BP存在下的本体光聚合,并指出氧对此聚合体系有加     

过硫酸盐-N,N,N',N'-四甲基乙二胺体系引发丙烯腈水溶液聚合

过硫酸盐与三乙醇胺或二乙醇胺组成的引发体系,能引发丙烯腈(AN)水溶液聚合。最近 Gupta等报道过硫酸盐-N,N,N′,N′-四甲基乙二胺(TMEDA)体系能在室温引发丙烯酰胺水溶液聚合。     

有机过氧化物与N,N-二(2-羟烷基)对甲苯胺体系引发烯类聚合及其机理的研究

 研究了有机过氧化物BPO,LPO分别与N,N-二(2-羟烷基)对甲苯胺DHET,DHPT组成的体系引发MMA的聚合。测定其聚合速度R_p,聚合表观活化能,聚合速度方程,聚合放热过程的温度与时间的关系。用自旋捕捉和ESR波谱技术,测定了上述体系反应产生的自由基中间体,同时通过聚合物端基分析证实DHET,DHPT组份产生的自由基能引发单体聚合。依据实验结果提出了这类体系的引发机理。     

基团转移聚合新引发剂——1-(N,N-二甲氨基)-1-三甲基硅氧基丁烯-1的合成与性质的研究

 本文报道了一种新的基团转移聚合引发剂——1-(N,N-二甲氨基)-1-三甲基硅氧基丁烯-1,对由其引发的GTP、其引发活性、与催化剂及单体用量比对聚合速度、分子量分布的影响进行了研究,得到了分散性较小的实测分子量和理论分子量相近的PMMA。     

含胺基功能性单体的聚合研究——Ⅵ.4-N′,N′-二甲氨基苯基N-取代丙烯酰胺的合成及其聚合

<正> 前文报道了含芳香叔胺基丙烯酸酯-甲基丙烯酸4-N,N-二甲氨基苄酯(DMABMA)的合成和聚合。这种在分子中既含有二甲氨基苯基,又含有双键的单体为“可聚合芳香叔胺”,在过氧化二酰如过氧化苯甲酰(BPO),过氧化月桂酰(LPO)引发下,芳香叔胺残基参与氧化还原引发体系,进而双键发生聚合反应。本文报道了二甲氨基苯基取代丙烯酰胺,即N-(4-N,N‘-二甲氨基苯基)丙烯酰胺(DMAPAA)和N-(4-N,N-二甲氨基苯基)甲基丙烯酰胺(DMAPMA)的合成及聚合。     

过渡金属盐催化甲基丙烯酸2-(N,N-二乙氨基)乙酯的自引发自由基聚合

研究了高氧化态过渡金属盐(CuX2/L、FeX3/L,X=C1或Br;L =2,2′-联吡啶、N,N'-四甲基乙二胺、N,N,N′,N″,N″-五甲基二亚乙基三胺;CuSO4)催化甲基丙烯酸2-(N,N-二乙氨基)乙酯(DEAEMA)的自引发氧化聚合,利用气相色谱跟踪单体转化率、利用凝胶渗透色谱和多角激光光散射跟踪聚合...     

含胺基功能性单体的聚合研究——Ⅲ.甲基丙烯酸4-(N,N-二甲氨基)苄酯在过氧化月桂酰引发下的聚合动力学

<正> 由芳香叔胺如N,N-二甲基对甲苯胺(DMT),N,N-二甲基苯胺(DMA)与过氧化苯甲酰(BPO)所组成的氧化还原体系以引发烯类单体的聚合已有较多报道,这种引发体系在医用高分子的硬组织材料如齿科材料,骨水泥的甲基丙烯酸甲酯(BMA)的低温快速固化上广被应用,构成这种氧化还原体系的低分子胺具有一定的毒性,其用量虽少,     

可聚合的二苯酮-脂肪叔胺光氧化还原体系敏化的丙烯腈光聚合

<正> 关于二苯甲酮-三级胺体系引发烯类单体光聚合的研究已有许多报道。其引发机理研究得也比较透彻。此类引发体系之所以引人注目,除其本身具有良好的引发效果外,还有重要的一点在于氧气对于此体系不但无阻聚作用,而且在一定条件下能够加速其聚合反应。甲基丙烯酸N,N-二甲氨基乙酯(DMAEMA)是可聚合的脂肪叔胺。有关芳香酮类如二苯甲酮。芴酮与DMAEMA构成的引发体系的研究已有城田等人和张举贤     

过硫酸盐-N,N,N′,N′-四甲基乙二胺体系引发乙烯基类单体聚合动力学的研究

研究了过硫酸盐-TMEDA体系引发丙烯酰胺、丙烯腈、甲基丙烯酸甲酯水溶液聚合的规律.发现[TMEDA]/[过硫酸盐]的比值起始增大时,聚合速度R_p与转化率都增大,但达到某一值后,如>5,R_p虽然增大而转化率反而下降.聚合物的分子量则总是下降,测定了三种单体聚合的表观活化能E_α和聚合速度方程。     

Tetraalkylammonium salt as photoinitiator of vinyl polymerization in organic and aqueous media: A mechanistic and laser flash photolysis study

N‐Dimethyl‐N‐[2‐(N,N‐dimethylamino)ethyl]‐N‐(1‐methylnaphthyl)ammonium tetrafluoroborate ( I ) was synthesized with the aim of obtaining a versatile photoinitiator for vinyl polymerization in organic solvents and water. Salt I was able to trigger the polymerization of acrylamide, 2‐hydroxyethylmethacrylate and styrene even at very low concentrations of the salt (～1.0 × 10^?5 M). Using laser flash photolysis and fluorescence techniques and analyzing the photoproduct distribution, we were able to postulate a mechanism for the photodecomposition of the salt. With irradiation, I undergoes an intramolecular electron‐transfer reaction to form a radical ion pair (RIP). The RIP intermediate decomposes into free radicals. The RIP and the free radicals are active species for initiating the polymerization. Depending on the concentration of the vinyl monomers studied, the initiation mechanism of the polymerization reaction changes. At large monomer concentrations, the RIP state is postulated to trigger the reaction by generating the anion radical of the olefin substrate. At a low monomer concentration, the free radicals produced by the decomposition of I are believed to start the chain reaction. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 901–913, 2002; DOI 10.1002/pola.10166     

Vinyl polymerization. 422. Initiation mechanism of uncatalyzed polymerization by polyethyleneglycol

The initiation mechanism on the radical polymerization of vinyl monomers by polyethyleneglycol (PEG-300) in aqueous solution was studied. The initiating radical species were determined by means of the spin trapping technique. They were concluded to be generated by the hydrogen atom transfer from the monomer adsorbed at the ether group of PEG-300 to the free monomer.     

Polymerization photoinitiated by carbonyl compounds. VI. Mechanism of benzil photoinitiation

The mechanism of the photoinitiation of the vinyl polymerization sensitized by benzil and 4,4′-dimethoxybenzil was studied. The monomers considered were methacrylic acid esters and styrene derivatives. All these monomers are efficient quenchers of the excited triplet benzil. However, the initiation efficiency of the benzil is important only when styrene derivatives are employed as monomers. The main polymerization process follows a simple free radical mechanism. The initiation step is a consequence of the interaction (triplet benzil–monomer double bond) through a charge transfer complex.     

Free‐radical polymerization of dioxolane and dioxane derivatives: Effect of fluorine substituents on the ring opening polymerization

Partially fluorinated and perfluorinated dioxolane and dioxane derivatives have been prepared to investigate the effect of fluorine substituents on their free‐radical polymerization products. The partially fluorinated monomer 2‐difluoromethylene‐1,3‐dioxolane (I) was readily polymerized with free‐radical initiators azobisisobutyronitrile or tri(n‐butyl)borane–air and yielded a vinyl addition product. However, the hydrocarbon analogue, 2‐methylene‐1,3‐dioxolane (II), produced as much as 50% ring opening product at 60 °C by free‐radical polymerization. 2‐Difluoromethylene‐4‐methyl‐1,3‐dioxolane (III) was synthesized and its free‐radical polymerization yielded ring opening products: 28% at 60 °C, decreasing to 7 and 4% at 0 °C and −78 °C, respectively. All the fluorine‐substituted, perfluoro‐2‐methylene‐4‐methyl‐1,3‐dioxolane (IV) produced only a vinyl addition product with perfluorobenzoylperoxide as an initiator. The six‐membered ring monomer, 2‐methylene‐1,3‐dioxane (V), caused more than 50% ring opening during free‐radical polymerization. However, the partially fluorinated analogue, 2‐difluoromethylene‐1,3‐dioxane (VI), produced only 22% ring opening product with free‐radical polymerization and the perfluorinated compound, perfluoro‐2‐methylene‐1,3‐dioxane (VII), yielded only the vinyl addition polymer. The ring opening reaction and the vinyl addition steps during the free‐radical polymerization of these monomers are competitive reactions. We discuss the reaction mechanism of the ring opening and vinyl addition polymerizations of these partially fluorinated and perfluorinated dioxolane and dioxane derivatives. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5180–5188, 2004     

Ab initio evaluation of the thermodynamic and electrochemical properties of alkyl halides and radicals and their mechanistic implications for atom transfer radical polymerization

High-level ab initio molecular orbital calculations are used to study the thermodynamics and electrochemistry relevant to the mechanism of atom transfer radical polymerization (ATRP). Homolytic bond dissociation energies (BDEs) and standard reduction potentials (SRPs) are reported for a series of alkyl halides (R-X; R = CH 2CN, CH(CH 3)CN, C(CH 3) 2CN, CH 2COOC 2H 5, CH(CH 3)COOCH 3, C(CH 3) 2COOCH 3, C(CH 3) 2COOC 2H 5, CH 2Ph, CH(CH 3)Ph, CH(CH 3)Cl, CH(CH 3)OCOCH 3, CH(Ph)COOCH 3, SO 2Ph, Ph; X = Cl, Br, I) both in the gas phase and in two common organic solvents, acetonitrile and dimethylformamide. The SRPs of the corresponding alkyl radicals, R (*), are also examined. The computational results are in a very good agreement with the experimental data. For all alkyl halides examined, it is found that, in the solution phase, one-electron reduction results in the fragmentation of the R-X bond to the corresponding alkyl radical and halide anion; hence it may be concluded that a hypothetical outer-sphere electron transfer (OSET) in ATRP should occur via concerted dissociative electron transfer rather than a two-step process with radical anion intermediates. Both the homolytic and heterolytic reactions are favored by electron-withdrawing substituents and/or those that stabilize the product alkyl radical, which explains why monomers such as acrylonitrile and styrene require less active ATRP catalysts than vinyl chloride and vinyl acetate. The rate constant of the hypothetical OSET reaction between bromoacetonitrile and Cu (I)/TPMA complex was estimated using Marcus theory for the electron-transfer processes. The estimated rate constant k OSET = approximately 10 (-11) M (-1) s (-1) is significantly smaller than the experimentally measured activation rate constant ( k ISET = approximately 82 M (-1) s (-1) at 25 degrees C in acetonitrile) for the concerted atom transfer mechanism (inner-sphere electron transfer, ISET), implying that the ISET mechanism is preferred. For monomers bearing electron-withdrawing groups, the one-electron reduction of the propagating alkyl radical to the carbanion is thermodynamically and kinetically favored over the one-electron reduction of the corresponding alkyl halide unless the monomer bears strong radical-stabilizing groups. Thus, for monomers such as acrylates, catalysts favoring ISET over OSET are required in order to avoid chain-breaking side reactions.     

Skewered reactions in free‐radical crosslinking (co)polymerizations of liquid polybutadiene as internal olefinic multivinyl crosslinker

As an extension of our continuing studies concerned with the mechanistic discussion of network formation in the free‐radical crosslinking (co)polymerization of multivinyl monomers, this work refers to the skewered reactions in the crosslinking (co)polymerizations of liquid polybutadiene rubber (LBR) as an internal olefinic multivinyl monomer or crosslinker, especially focused on the competitive occurrence of both addition or skewered reaction to internal carbon–carbon (CC) double bonds and abstraction reaction of allylic hydrogens in LBR by growing polymer radical. Thus, LBR is regarded as an internal olefinic multiallyl monomer‐linked allyl groups (? CH?CH? CH₂? ) with methylene units (? CH₂? ). First, gelation in the polymerization of LBR was explored in detail, especially at elevated temperatures. The occurrence of intermolecular crosslinking was easier in the order LBR > LBR containing 20 mol % of 1,2‐structural units > liquid polyisoprene rubber. Then, we pursued the polymerization of LBR using dicumyl peroxide (DCPO) as typical organic peroxide used at elevated temperatures. The primary cumyloxy radical generated by the thermal decomposition of DCPO may add to CC double bond or abstract allylic hydrogen or undergo β‐scission to generate a secondary methyl radical. The initiation by the cumyloxy radical was omitted. The ratio of allylic hydrogen abstraction to β‐scission reaction was estimated; thus, only 39% of cumyloxy radical was used for the allylic hydrogen abstraction reaction. The addition of methyl radical to CC double bond was clearly observed. Finally, we pursued the intermolecular and intramolecular skewered reactions in free‐radical crosslinking LBR/vinyl pivalate copolymerizations. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Metal chelates in vinyl polymerization: Bulk polymerization of acrylonitrile initiated by Cu(II)–imine complexes

This article deals with the kinetics and mechanism of acrylonitrile (AN) polymerization initiated by Cu(II)–4-anilino 3-pentene 2-one[Cu(II)ANIPO], Cu(II)–4-p-toluedeno 3-pentene 2-one [Cu(II)TPO], and Cu(II)–4-p-nitroanilino 3-pentene 2-one [Cu(II)NAPO] in bulk at 60°C. The polymerization is free radical in nature. The exponent of initiator(I) is ? 0.5. The initiation step is a complex formation between the chelate and monomer and subsequent decomposition of the intermediate complex giving rise to free radical and Cu(I). This is substantiated by ultraviolet (UV) and electron spin resonance (ESR) studies. The activation energies and kinetic and chain transfer constants have also been evaluated.     

Metal-Containing Initiator Systems. IX. Radical Polymerizations of Vinyl Monomers by Various Metal Acetylacetonates

Abstract

A study of the polymerization of styrene, methyl methacrylate, acrylonitrile, vinyl acetate, and vinyl chloride initiated by various metal acetylacetonates [Me(acac)_x] has been made. It was found that Mn(acac)₃ was the most effective initiator, and Co(acac)₃, Mn(acac)₂, Cu(acac)₂, and Cr(acac)₃ showed moderate activity for the polymerization of methyl methacrylate at 60°C. However, the other, Me(acac)_x, had no effect or served as inhibitors. The addition of some additives such as halogen compounds did not accelerate polymerization of methyl methacrylate by Mn(acac)₃, From the results of polymerization and copolymerization of methyl methacrylate by Mn(acac)₃, it was concluded that the polymerization proceeded via an ordinary radical mechanism and the activation energy for initiation was 25.2 kcal/mole. The initiation mechanism of vinyl polymerization by Me(acac)_x was studied on the basis of the complex formation with the monomer.     

The initiation of the free radical polymerization of vinyl monomers by hexakis(arylisocyano) derivatives of chromium (o)

The present paper describes studies carried out to determine the effect of structure on the free radical polymerization of vinyl monomers initiated by means of the hexakis(arylisocyano) derivatives of chromium (o) in which chlorine, methoxy, and methyl groups have been substituted into different positions of the benzene ring. The kinetics of the initiation reactions resembles that studied in detail for the parent compound hexakis(phenylisocyano) chromium (o). The observed changes in the initial rates of the polymerization of methyl methacrylate at 80°C in the presence of carbon tetrachloride can be accounted for by the electronic effects associated with these substituents. However, when steric overcrowding occurs, the initial rates of polymerization are reduced considerably. The results obtained confirm the mechanism of initiation proposed earlier in which the rate determining step is the S_n² displacement of an arylisocyano ligand by a monomer or reactive solvent molecule. An attempt has been made to explain the increased rate of radical formation observed when chlorine is substituted into the benzene ring.     

Photoinitiated free radical polymerization of vinyl compounds in aqueous solution

A new method for the photochemical initiation of polymerization of vinyl compounds in aqueous solution is described. The photochemically active species is an ion pair complex of the formula Fe³⁺X⁻(X⁻ = OH⁻, CI⁻, N⁻₃, etc.). The light absorption by the ion pair leads to an electron transfer causing reduction of the cation and oxidation of the anion to an atom or free radical X. The latter leads to the initiation of polymerization in accordance with X + CH₂CHR→XCH₂ CHR . The kinetics of the reaction were studied by the measurement of: (a) ferrous ion formed (colorimetrically), (b) monomer disappearance (by titration and by weighting the polymer), (c) the chain length of the polymer (in the case of methyl methacrylate). The dependence of the quantum yield on the light intensity, light absorption fraction, and the concentration of vinyl monomer and ferrous ion added initially was investigated. A complete mechanism, both with regard to the formation of free radicals and the polymerization reaction, was put forward involving: (1) light absorption, (2) a primary dark back reaction, (3) dissociation of the primary product, (4) a secondary dark back reaction, (5) initiation of polymerization by free radicals, (6) propagation of polymerization, and (7) termination by recombination of active polymer endings. The mechanism was verified by the experimental results and some constant ratios were estimated quantitatively.