Equilibrium Cationic Polymerization of Tetrahydrofuran in Benzene

Abstract

The equilibrium cationic polymerization of tetrahydrofuran in benzene is investigated in the 15 to 50°C range. Polymerizations are initiated with triethyloxonium hexafluorophos-phate (Et₃O⁺PF₅ ^?) and performed using high vacuum techniques. It is shown that, at a given temperature, the equilibrium monomer concentration varies linearly with polymer concentration. Values of ΔG_lc, the free-energy change upon the polymerization of 1 mole of liquid monomer to 1 base-mole of liquid amorphous polymer of infinite chain length, is deduced from these results. Values of ΔG_lc, obtained are in good agreement with those found in the literature for the equilibrium polymerization of tetrahydrofuran in bulk, However, there is a large discrepancy between these values of     

近红外原位研究杂多酸引发的环氧-四氢呋南阳离子聚合

用近红外光谱原位跟踪的方法,研究了杂多酸催化的环氧树脂和四氢呋喃的阳离子聚合过程.发现在低环氧树脂含量下,环氧消耗速率在整个聚合过程中维持不变;而在高环氧树脂含量下,环氧消耗速率则随时间有所下降.通过红外光谱在碳氢区域的分峰分析,证明环氧树脂与四氢呋喃发生了共聚反应,二维红外光谱的结果也确证了这一结果.此外,还探讨了环氧转化速率与环氧含量间的关系.     

近红外原位研究杂多酸引发的环氧-四氢呋喃阳离子聚合

用近红外光谱原位跟踪的方法, 研究了杂多酸催化的环氧树脂和四氢呋喃的阳离子聚合过程. 发现在低环氧树脂含量下, 环氧消耗速率在整个聚合过程中维持不变; 而在高环氧树脂含量下, 环氧消耗速率则随时间有所下降. 通过红外光谱在碳氢区域的分峰分析, 证明环氧树脂与四氢呋喃发生了共聚反应, 二维红外光谱的结果也确证了这一结果. 此外, 还探讨了环氧转化速率与环氧含量间的关系.     

Time and Temperature Dependence of Macro-ion-Macro-ester Equilibrium in the Cationic Polymerization of Tetrahydrofuran by HOSO2F

Reactivity and equilibrium of two active species-tertiary oxonium ion (TOI) and superacid ester (SAE)-in the system of cationic polymerization of tetrahydrofuran (THF) initiated by fluorosulfonic acid (FSO₃H) in dichloromethame has been studied. In the given system, it was found that TOI is mainly responsible for the polymerization at the initial stage; however, the cocentration of TOI decreases rapidly with the progress of polymerization and finally becomes almost untraceable. On the other hand, [SAE] monotonically increases as the polymerization proceeds. The stability of TOI appears less than that of SAE under the given reaction conditions. Results demonstrate that both the progress of polymerization and increase in temperature favor the formation of SAE.     

Cationic Polymerization of Tetrahydrofuran with Fuming Sulfuric Acid Initiator: Effects of Superacid Salts and Aromatic Compounds on Mn and Yield of the Polymer

Bulk polymerization of tetrahydrofuran was studied to find a facile method for the preparation of polytetramethyleneglycol having molecular weight more than 1000 initiated by fuming sulfuric acid as a main component at -5 to 0°C. Superacid salts, being soluble in tetrahydrofuran, showed excellent activity for increasing the molecular weight. The polymerization initiated by fuming sulfuric acid in combination with sodium trifluoromethane sulfonate was examined under several conditions. It was also found that a mixture of fuming sulfuric acid and an aromatic compound such as benzenesulfonic acid, benzene, and xylene, contributed to an increase in the molecular weight of polymer.     

Studies on Phosphorus-Containing Polymers. V. Ring-Opening Polymerization of Tetrahydrofuran Catalyzed by Linear Phosphonitrilic Chloride

It was found that linear phosphonitrilic chloride could be used as a catalyst for ring-opening polymerization of tetrahydrofuran. Bulk polymerizations were carried out in a nitrogen atmosphere. After termination of polymerization, the reaction mixture was poured into water, thereby decomposing the catalyst. The product was dissolved in benzene and then subjected to lyophilization. The polymerization of tetrahydrofuran in the presence of linear phosphonitrilic chloride was found to be an equilibrium and a “living” polymerization. The polymerization product includes little phosphorus, and its infrared absorption spectrum agrees well with that of the polymer obtained with PF₅ catalyst. The results of the polymerization using epichlorohydrin as a promoter show that the number of active sites in the molecule of linear phosphonitrilic chloride is considerably smaller. Consequently it is conceivable that the catalytic activity of the linear phosphonitrilic chloride is attributed to its terminal ～～P⁺Cl₃PCl_?6 structure. Furthermore we presume that the polymerization of tetra-hydrofuran in the presence of this catalyst proceeds through a cationic ring-opening mechanism.     

Effect of the Counterion on the Cationic Polymerization Rate of Ethylene Oxide by Trityl Salts

The cationic polymerization of ethylene oxide by trityl salts (BF₄ ^?, SbCl₆ ^?, AsF₆ ^?, and PF₆ ^? as counterions) in nitrobenzene at different temperatures has been studied. The kinetic analysis was carried out by use of an automatic manometer, and it showed that the polymerization rate constant depends neither on the counterion type nor on the initial initiator concentration. These facts allowed us to conclude that macrocations and macroion pairs have the same reactivity.     

离子液体/季铵盐辅助氯过氧化物酶促氧化合成聚酚

基于氯过氧化物酶(CPO)催化氧化苯酚衍生物单体,建立了一个聚酚的绿色合成体系.以对苯基苯酚、对甲基苯酚、4-乙基苯酚、对羟基肉桂酸、对异丙基苯酚和邻甲基苯酚等6种底物为考察对象,以聚合物的产率、聚合度及热稳定性为评价指标,研究了体系中引入离子液体(ILs)或季铵盐(QAS)以及底物结构和反应微环境等对聚合反应和聚合物性质的影响.结果表明,引入少量咪唑类ILs或QAS可有效提高产物收率,其中ILs/QAS的阳离子基团越大和疏水链越短,越有利于酶催化聚合反应的进行;而ILs/QAS添加量的影响则呈现"钟罩"型规律.同时,苯酚对位取代远比邻位取代有利于聚合反应进行;而对位取代基中烷基类给电子基团比芳香基取代更有优势,所得聚合物的聚合度和热稳定性相对增大,但随着取代基团的增大,其空间位阻不利于聚合物产率的提高;反应体系的p H应控制在弱酸性至近中性,以避免竞争性的副反应的发生;而氧化剂H_2O_2则需要采用间歇式加入以抑制瞬时过浓导致CPO活性中心卟啉环的氧化损伤.基于CPO的活性中心结构分析了聚合机理.     

Microwave Effects Due to Anionic or Cationic Initiators in Emulsion Polymerization Reactions

Summary: Emulsion polymerization reactions were performed under microwave irradiation and conventional heating using anionic or cationic initiators and surfactants. Microwave irradiation promoted higher reaction rates for both initiators and surfactants, in comparison with the conventional heating. The effect of high power microwave irradiation was studied using a method of cycles of heating and cooling, where rapid polymerization reactions were obtained. In the reactions with anionic initiator and surfactant, a decrease in the particle diameters was observed with microwave heating, and even smaller particles were obtained using high power microwave irradiation. Moreover, the decrease in the particle size was acompanied by an increase in the polymer molecular weight. On the other hand, these effects were not observed for reactions with cationic initiator and surfactant.     

Cationic Zinc Hydride Catalyzed Carbon Dioxide Reduction to Formate: Deciphering Elementary Reactions,Isolation of Intermediates,and Computational Investigations

Zinc has been an element of choice for carbon dioxide reduction in recent years. Zinc compounds have been showcased as catalysts for carbon dioxide hydrosilylation and hydroboration. The extent of carbon dioxide reduction can depend on various factors, including electrophilicity at the zinc center and the denticity of the ancillary ligands. In a few cases, the addition of Lewis acids to zinc hydride catalysts markedly influences carbon dioxide reduction. These factors have been investigated by exploring elementary reactions of carbon dioxide hydrosilylation and hydroboration by using cationic zinc hydrides bearing tetradentate tris[2-(dimethylamino)ethyl]amine and tridentate N,N,N′,N′′,N′′-pentamethyldiethylenetriamine in the presence of triphenylborane and tris(pentafluorophenyl)borane.     

改性羰基钴催化氢甲酰化反应系列基元反应的理论研究

在HF/LANL2DZ水平下,采用有效核势能近似(ECP)从头算方法,研究了有机膦配体改性羰基钴催化的氢甲酰化反应循环中部分基元反应步骤的微观反应机理.优化了基态势能面上诸反应中间体、过渡态和产物的几何构型.计算了反应活化位垒.结果表明,羰基插入、加氢氧化和脱氢还原的基元反应步骤的活化位垒分别为54.02,134.02和43.44kJ/mol.     

High Molecular Weight Polystyrene Obtained by Cationic Emulsion Polymerization Catalyzed by Imidazolium‐Based Ionic Liquid

The ionic liquid 1‐n‐butyl‐3‐methylimidazolium heptachlorodiferrate (BMI.Fe₂Cl₇) is efficiently used as catalyst in the cationic emulsion polymerization of styrene. The effect of different reaction temperatures, surfactant, and ionic liquid concentrations on polymer properties as molecular weight distribution and particle size is evaluated. High weight average molecular weights, above 1000 kDa, are achieved at 70% of conversion in 100 nm polystyrene particles formed mainly by micellar nucleation. Particle sizes and molecular weights increase with the decrease of the amount of surfactant. Even at low concentrations, BMI.Fe₂Cl₇/styrene molar ratio equal to 1/1000, the ionic liquid proves to be efficient for the emulsion polymerization of styrene, and lower ionic liquid concentrations lead to the formation of longer polymer chains.     

Rate Constant of Initiation Reaction in Cationic Polymerization of Vinyl Monomers. I. Polymerization of Styrene Derivatives Catalyzed by Triphenylmethyl Stannic Pentachloride

Abstract

To investigate the method of measurement of the initiation rate constant in cationic polymerization, styrene and α-methylstyrene are polymerized by triphenylmethyl stannic pentachloride (Ph₃CSnCl₅). Adding these monomers to a solution of Ph₃CSnCl₅, the strong absorption of triphenylmethyl cation at 400 to 450 mμ disappears. The rate of disappearance of the absorption at 430 mμ is proportional to the concentration of Ph₃CSnCl₅ and monomer. It is confirmed that this disappearance of the absorption is due to the conversion of triphenyl cation to styryl or α-methylstyryl cation. Therefore, the rate of consumption of triphenylmethyl cation corresponds to that of the addition of triphenylmethyl cation to the olefinic double bond in a monomer, that is, the rate of the initiation reaction. Considering the dissociation constant of Ph₃CSnCl₅, the initiation rate constants of styrene and α-methylstyrene in ethylene chloride solution at 30°C are 11.6 × 10^?2 and 2.85 liters/mole-min, respectively. These values seem to be much smaller than the propagation rate constant of each monomer. However, the effect of polymerization conditions, for example, the kind of a monomer and the polarity of a solvent, on the initiation rate constant is the same as in the propagation reaction. This fact suggests the similarity of a reaction mechanism in both elementary reactions.     

铯盐促进的有机反应

铯盐如Cs₂CO₃, CsF等因在钯催化碳碳偶联, N, O, S的烃基化反应中表现出良好的性能而引起了人们的广泛关注. 介绍了铯盐在钯催化的Suzuki, Heck, Stille, Sonogashira反应, 烯醇盐的芳基化, 酚类的邻位芳基化以及羰基化反应中的促进作用. 同时还对铯盐参与的N, O, S等的烃基化反应进行了讨论, 并侧重于与其他碱金属盐的对比.     

Cocatalysis in Cationic Polymerization

Problems concerned with the principles of cocatalysis and coinitiation as a part of cationic polymerization are discussed. When the established concept of different reactive particles, i.e., contact and separated ion-pairs or free ions, is applied to cationic initiation and propagation centers, then common features for one general process can be drawn even in so diverse cases as “pseudocationic” polymerization, solvent “cocatalysis,” polymerization during condensation and induced by co-monomer addition. A special case of activation by solvent is “cocatalysis” by water.

The model for these cases was found during the interpretation of waves observed on styrene polymerization curves. The formation of ion-pairs proceeds spontaneously. The activation and deactivation of these ion-pairs is effected via coordination of suitable molecules with the former, i.e., by equilibrium shifts     

羟基钴催化氢甲酰化反应的理论研究

采用有效核势能近似(ECP)从头算方法,在HF/LANL2DZ水平下研究了羰基钴催化的氢甲酰化反应循环中的羰基插入、H2 氧化加成和脱氢还原系列基元反应步骤的反应机理.优化得到了反应基态势能面的中间体、过渡态和产物的几何构型.计算了反应活化位垒,并对各过渡态进行了振动分析以确认.理论计算结果表明,羰基插入、H2 氧化加成、脱氢还原的基元反应步骤的活化位垒分别为67.79、139.11和44.78kJ·mol-1.     

环氧氯丙烷促进磷钨酸引发四氢呋喃聚合

环氧氯丙烷促进磷钨酸引发四氢呋喃聚合;聚四氢呋喃;开环聚合;     

微乳液催化苯乙烯聚合反应

微乳液催化苯乙烯聚合反应１）郝京诚汪汉卿２）（中国科学院兰州化学物理研究所兰州７３００００）石元昌李干佐（山东大学胶体与界面化学研究所济南２５０１００）关键词微乳液催化苯乙烯聚合微乳液［１］是油、水、表面活性剂和助表面活性剂在适当比例下自发形成的热力...