Anionic polymerization of ethylene oxide with cryptates as counterions: 1

A kinetic study of the anionic polymerization of ethylene oxide has been made in tetrahydrofuran at 20°C, with the cryptate K⁺ + [222] as counterion. The ion pair dissociation constant K_D has been deduced from conductivity measurements made on seeds solutions. Some ionic associations higher than cryptated ion pairs could be detected but they are negligible for living end concentrations lower than 6 × 10^?4 mol/l. k_± and k_? were determined from both sets of kinetic data obtained with and without added salt. Free alkoxide ions are one hundred times more reactive than cryptated ion pairs.     

Anionic polymerization of α,α-disubstituted β-propiolactones with cryptates as counterions

A kinetic study of the anionic polymerization of α-methyl-α-propyl-β-propiolactone has been made in tetrahydrofuran at ?20°C, with the cryptate K⁺+[222] as counter-ion. Conductance measurements have been made on THF solutions of potassium β-naphthoate complexed by [222] as a model of cryptated carboxylates. Propagation reaction proceeds through cryptated ion pairs and free ions. Cryptated carboxylate ion pairs are more reactive than free ions.     

Anionic polymerization of 2-haloethyl methacrylates

The anionic polymerizations of 2-chloroethyl methacrylate (1), 2-bromoethyl methacrylate (2), and 2-iodoethyl methacrylate (3) were carried out in THF at −78 °C with 1,1-diphenyl-3-methylpentyllithium in the presence of LiCl. The polymerizations proceeded in a controlled manner to quantitatively afford polymers with predictable molecular weights and narrow molecular weight distributions. Under similar conditions, the anionic block copolymerizations by the sequential addition of methyl methacrylate (MMA) followed by 1, 2, and 3 generated the corresponding diblock copolymers with well-defined structures. On the other hand, in the block copolymerization by the reverse addition of monomer, a well-defined diblock copolymer, poly(1)-block-PMMA, could be synthesized only by the sequential addition of 1 followed by MMA, whereas the block copolymerizations using 2 and 3 were not successful because of instabilities of the propagating chain-end anions derived from 2 and 3. The side reactions which occurred during the polymerization were discussed.     

间甲基苯酚钾为调节剂的异戊二烯负离子聚合反应

考察了间甲基苯酚钾(m-ROK)用量对正丁基锂(n—BuLi)／m—ROK／二乙二醇二甲醚／异戊二烯／二甲苯负离子聚合体系的链转移反应、聚异戊二烯相对分子质量及微观结构的影响。结果表明,当m—ROK／n—BuLi(摩尔比)小于0．5时,聚异戊二烯的特性黏数和相对分子质量迅速下降,链转移次数增加;当m—ROK／n—BuLi(摩尔比)大于0．5时,则不遵循此变化规律。m—ROK的加入明显加宽了聚异戊二烯的相对分子质量分布。增加m—ROK用量时,聚异戊二烯微观结构中1,2-结构和3,4-结构质量分数下降,1,4-结构质量分数增加。     

Cationic polymerization of ethylene oxide with Maghnite‐H as a clay catalyst in the presence of ethylene glycol

The activated‐monomer cationic ring‐opening polymerization of ethylene oxide, initiated with ethylene glycol and using an acid‐exchanged montmorillonite clay called Maghnite‐H⁺ as an effective catalyst, was carried out to obtain the corresponding homopolymers with narrow polydispersity ratios. The molecular weights of the obtained polymers were controlled with the feed ratio of the monomer to the initiator. The effects of the amount of the catalyst and time on the polymerization yield and viscosity of the polymers were studied. The structure was confirmed with proton nuclear magnetic resonance and matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Ring-opening polymerization of ethylene oxide by anion initiation using sulfadiazine as parents compound

A new kind of anion initiator using sulfadiazine as the parent compound was prepared by the reaction of sulfadiazine with epoxy ethylene, and then the metal potassium. The structure of the intermediate was characterized in detail by NMR, MS, UV, IR, and DSC. Ring-opening polymerization of epoxy ethylene could be carried out by this initiation system. The molecular weight of the polymerized product, polyethylene oxide with a sulfadiazine end group (PEO_sf), is in the range of 3000–4000. © 1995 John Wiley & Sons, Inc.     

Anionic polymerization of dienes using oligobutadienyl-lithium as initiator

The aim of this work is to combine the microstructure of a radical-polymerized diene (butadiene and isoprene) with the functionality of an anionically prepared one, which could be used for polyurethane preparation after functionalization. A two-step anionic procedure was used in order to obtain a hydrocarbon-soluble lithium-based initiator. When compared with the related anionic polymers obtained under classical conditions, the vinyl content of the polydienes was three times greater. These findings are discussed on a mechanistic basis. © 1998 Society of Chemical Industry     

间甲基苯酚钾为调节剂的丁二烯负离子聚合反应

在正丁基锂(n-BuLi)／间甲基苯酚钾(m—ROK)／二乙二醇二甲醚／丁二烯／二甲苯的负离子聚合体系中,研究了m—ROK用量对链转移反应、聚丁二烯相对分子质量及微观结构的影响。结果表明。当m—ROK／n—BuLi(摩尔比)小于0．5时,聚丁二烯的特性黏数和相对分子质量迅速下降,链转移次数增加;当m—ROK／n—BuLi(摩尔比)大于0．5时,则不遵循此变化规律。m—ROK的加入明显加宽了聚丁二烯的相对分子质量分布。增加m—ROK用量时,聚丁二烯的微观结构中1,2-结构质量分数下降,顺式-1,4-结构和反式-1,4-结构质量分数增加。     

Anionic polymerization of acrylates

Summary The article presents preliminary results of the anionic polymerization of 2-ethylhexyl- and butyl acrylates initiated by ester enolate in the presence of Li 3-methylpentoxide-3. Compared with the Li t-butoxide which has been widely used earlier, this alkoxide is a more efficient stabilizer of active centers. Under selectively chosen reaction conditions, polymerizations of both monomers proceed quantitatively with a small extent of the selftermination event at-40 and-20°C producing polymers with narrow MWD's.     

Anionic polymerization of vinylsilanes

Summary The anionic polymerization of dimethylphenylvinylsilane with sec-butyllithium/N,N,N,N-tetramethylethylenediamine (TMEDA) was investigated. The polymerization proceeded up to 100% yield and afforded the polymer having isomerized-structure units. The polymerization was accompanied by chain transfer reaction to the monomer and the polymerization rate in the presence of TMEDA was much lower than in the absence of TMEDA.     

MgCl2-BuOH/TiCl4催化剂催化乙烯聚合动力学

研究了MgCl2-正丁醇/TiCl4催化剂常压下催化乙烯聚合的性能和动力学行为.考察了n(Al)/n(Ti)、聚合温度、共聚单体浓度、氢气分压对催化剂性能的影响.研究表明:三乙基铝为助催化剂,n(Al)/n(Ti)为200,聚合压力为0.1 MPa,温度为50℃,聚合时间为2 h时,该催化剂具有较高的活性:聚合动力学行为平稳,活性衰减较慢,活性可达1 550.2 g/g;该催化剂具有良好的乙烯均聚合和共聚合性能以及氢调性能.     

Anionic polymerization of styrene: Integration with styrene monomer production

Anionic polymerization and ethylbenzene dehydrogenation were carried out in the laboratory using continuous reactor designs and conditions typical of current commerical processes. The dehydrogenator was operated at 43–55% conversion with continuous distillation of the ethylbenzene/styrene mixture to remove byproducts that would interfere with the subsequent anionic polymerization. The anionic polymerization was carried out using a reactor of the CSTR type which operated at > 99% conversion of styrene. The volatiles were recovered from the polymer syrup and recycled back to the dehydrogenator. During 4 months of continuous operation the integrated process showed no detrimental buildup of impurities which affected the anionic polymerization or dehydrogenation. The polystyrene produced had excellent color, clarity, thermal stability, and polydispersity (M_w/M_n = 2.1–2.4). The ability to control weight average molecular weight was within a range of 20,000 using an on-line GPC in concert with a colorimeter.     

Anionic polymerization of vinylsilanes VII

Summary. The anionic polymerization of tetravinylsilane (TeVS) was carried out in the presence and absence of N,N,N',N'-tetramethylethylenediamine (TMEDA). Without TMEDA, the polymerization proceeded extremely slowly and the polymer yield was still low even after an extended polymerization time. When TMEDA was added to the system, the polymerization was remarkably accelerated and gelation was suppressed. Such polymerization behavior of TeVS is closely similar to that of methyltrivinylsilane under similar conditions. The effects of TMEDA are explained by its coordination to the propagating end that increases the selectivity in the reaction of the propagating end with vinyl groups. Received: 29 March 1997/Revised: 14 July 1997/Accepted: 18 July 1997     

Anionic polymerization of methyl acrylate

The homogeneous polymerization of methyl acrylate in tetrahydrofuran using a variety of sodium aryl catalysts has been investigated at ?75°C and ?30°C. The mode of action of each catalyst is discussed and its efficiency in producing high polymer has been calculated from the yields and polymer characteristics. Sodium trityl is the most effective catalyst at both temperatures. Dilatometry has shown that with sodium naphthalene at ?70°C, rapid initial polymerization to about 10% conversion in 4 min is followed by a very low rate period which proceeds at low temperature for at least 24 h when conversions up to 50% have been observed. Throughout this period a species is present which absorbs at 320 nm and which is immediately lost on addition of a proton donor. There is evidence suggesting that this dormant form of the poly(methyl acrylate) anion is an oxyanion. It is postulated that carbanions are formed initially and are responsible for the rapid polymerization rate. They also isomerize in an equilibrium reaction to form the unreactive oxyanions. The rate of further propagation is thus controlled by the value of the equilibrium constant which in this system is strongly in favour of the oxyanions. On the basis of this mechanism some rate constants have been calculated.     

负载茂金属催化剂催化乙烯气相聚合

研究了负载茂金属催化剂(n-BuNeCp)_2ZrCl_2/SiO_2的乙烯气相聚合行为及其催化聚合产品的性能。三乙基铝加入聚合体系后可降低负载茂金属催化剂的初始活性,有利于聚合过程中的温度控制。气相聚合产品聚乙烯的重均分子量为(1 42～2.28)×10~5,相对分子质量分布为2.6～3.1,熔点在135℃以上,结晶度约为60%,聚乙烯产物颗粒形态以球形为主.堆密度大于0.35 g/cm~3。     

Anionic polymerization of fluorine-containing vinyl monomers

Summary The anionic polymerization of pentafluorophenylmethyl methacrylate (PFPMA) were examined with several anionic initiators. The initiators of relatively low activity such as t-C₄H₉OK, organozinc compounds and Al(C₂H₅)₃ produced poly(PFPMA) in fairly high yields though no polymer was obtained by the initiations of n-C₄H₉Li and C₂H₅MgBr within 7 days. The anionic polymerization reactivity of PFPMA was found to be strongly affected by the pentafluorophenyl group though the e-value of PFPMA is similar to those of methyl methacrylate and benzyl methacrylate.Part 7, Polym. J. 19, 958 (1987)     

Study on anionic polymerization of ethylene oxide initiated by ammonium/triisobutylaluminum

In this paper, ammonium/triisobutylaluminum was used as an initiating system for anionic polymerization of ethylene oxide (EO). When the amount of triisobutylaluminum versus ammonium was in excess, a fast polymerization rate was achieved at room temperature and allowed polyethylene glycol synthesized with a high molecular weight and narrow molecular weight distribution. It was found that triisobutylaluminum may play two roles during the polymerization, one is that it can react with ammonium to form “ate” complex as an efficient initiator for EO polymerization, and the other is that it exerts a significant activating effect on the monomer. The catalytic effect of triisobutylaluminum in EO polymerization was elucidated by using quantum chemical calculations at density functional theory level, involving thermo-chemistry parameters. The studies show that EO homopolymerization cannot be conducted without the aid of catalyst due to the big energy difference of bonding orbitals. The interaction between EO and trialkylaluminum makes the electron cloud distribution and energy gap of EO molecule change, which indicates trialkylaluminum can activate the monomer. In addition, because of the lower enthalpy of formation, the formation of “ate” complex is prior to the interaction of trialkylaluminum and EO.     

Anionic polymerization of styrene in 2-methyltetrahydrofuran: temperature dependence of the field effect

Kinetics of living anionic polymerizations of styrene was investigated for lithium, sodium, and potassium salts in 2-methyltetrahydrofuran at 35, 25, 0, and ?70°C in the presence and absence of a high intensity electric field. At 35 and 25°C, a field acceleration effect was observed whereas no effect was found at 0 and ?70°C. The propagation rate constant of ion pairs was almost independent of gegen ions and their temperature dependence was smaller than that of free anions. The free ions seem to be more strongly solvated as the temperature decreases.     

Toward a CO2-free ethylene oxide process: Homogeneous ethylene oxide in gas-expanded liquids

Among industrial chemical processes, ethylene oxide manufacture emits the largest amount of CO₂ (∼2-3 million tons/yr), as byproduct from the burning of both the ethylene (feed) and ethylene oxide. Further, the conventional silver-based catalytic process presents safety challenges due to the formation of explosive ethylene oxide/O₂ mixtures in the gas phase. By judicious choice of the catalyst (methyltrioxorhenium), oxidant (H₂O₂) and reaction medium (methanol/water), a homogeneous liquid phase catalytic system has been demonstrated that eliminates CO₂ formation while producing ethylene oxide at >90% selectivity at near-ambient temperatures. Given its high volatility, the ethylene oxide is easily recovered from the reaction phase by distillation. The vicinity of the gaseous ethylene feed to its critical temperature (9 °C) is exploited to significantly increase its solubility in the liquid reaction phase by facile compression beyond the critical pressure of ethylene (∼50 bar). Since H₂O₂ is stable at typical reaction temperatures (40 °C or less), potentially explosive ethylene oxide/O₂ mixtures are avoided in the gas phase. In addition to the potential of arresting the carbon footprint of a large-scale industrial process, the demonstrated process concept shows how gas-expanded liquids can be generally exploited in homogeneous catalysis to enhance productivity.