Polymerization of butadiene with a halogen-containing trans-regulating neodymium-magnesium catalytic system in the presence of carbon tetrachloride

The polymerization of butadiene in toluene initiated by the NdCl₃ · 3TBP-Mg(C₄H₉)(i-C₈H₁₇) (TBP is tributyl phosphate) catalytic system has been studied. It has been shown that the polymerization reaction under study is a nonstationary slowly initiated process. The addition of carbon tetrachloride promotes an increase in the catalytic activity of the system. The products of polymerization have low molecular masses and polydispersity indexes. The content of 1,4-trans-units in the polymer is as high as 95%.     

Reversible addition-fragmentation chain transfer polymerization of methacrylate, acrylate and styrene monomers in 1-alkyl-3-methylimidazolium hexfluorophosphate

1-alkyl-3-methylimidazolium hexfluorophosphate ([C_x][PF₆], where x=4, 6-8) is used as solvent for the polymerisation of methyl methacrylate, methyl acrylate and styrene by the reversible addition-fragmentation chain transfer process. In the case of styrene, the insolubility of the polymer in ionic liquid stops the polymerization at an early stage. The acrylate and methacrylate polymerizations lead to products with molecular weights close to the theoretical ones and polydispersity indexes lower than 1.3. The polymerizations are shown to be living by chain extension of the products formed in ionic liquid. In the case of the methyl methacrylate, the kinetics of the polymerizations are followed and the molecular weight of the polymer is shown to increase linearly with the conversion, as expected for a living polymerization.     

The thermolysis of ethyltrichlorosilane and ethyltrimethylsilane

The thermal decompositions of ethyltrichloro-and ethyltrimethyl-silane have been studied in the gas phase at 823K. The main primary process in each case is the dehydrosilylation reaction X₃SiCH₂CH₃ → X₃SiH+CH₂ = CH₂ (X = Cl or Me), though several additional products are formed, mainly in secondary reactions. It is concluded that the dehydrodesilylations involve a radical chain sequence, and that the formation of vinyl chloride by dehydrosilylation during the thermolysis of (2-chloroethyl) trichlorosilane probably also follows a radical pathway rather than the four-centre molecular process previously suggested.The following reactions at ca. 823K have also been briefly examined: (i) the thermal decomposition of trichlorosilane; (ii), the interaction of ethylene and tri-chlorosilane; (iii) the thermal decomposition of vinyltrichlorosilane.     

Oxidative polymerization of diphenylamine: A mechanistic study

The mechanism of oxidative polymerization of diphenylamine is considered. The kinetic study of diphenylamine polymerization and of the structure and molecular-mass characteristics of the reaction products has shown that the degree of oxidation of intermediates plays the key role in polyrecombination. The relationship between the polymerization procedure and the molecular mass of polydiphenylamine was revealed.     

Cationic polymerization of isobutylene with H2O/TiCl4 initiating system in the presence of electron pair donors

Cationic polymerization of isobutylene (IB) in a mixture of methylene dichloride (CH₂Cl₂) and n-hexane (n-Hex) was conducted by using H₂O as initiator, TiCl₄ as co-initiator in the presence of strong external electron pair donor (ED), such as pyridine (Py), dimethylacetamide (DMA) or triethylamine (TEA). The effects of ED concentration, TiCl₄ concentration, solvent polarity, polymerization temperature (T) and time on IB polymerization, molecular weight (MW) and molecular weight distribution (MWD, M_w/M_n) of polyisobutylene (PIB) products were investigated. The relative amount of polymer formed via uncontrolled initiation by conventional active species (I) decreased with increasing the solvent polarity, TiCl₄ concentration and ED concentration in the polymerization. The desirable polymerization of IB with apparent absence of chain transfer reactions could be obtained by H₂O/TiCl₄ initiating system in the presence of ED under the appropriate reaction conditions. The external electron pair donors and TiCl₄ did specially play important and effective roles on polymerization.     

Production of organometallic polymers by the interfacial technique. V. Partial mechanistic study of the production of poly[alkyl(aryl)oxysilances]

A modified interfacial polymerization system capable of producing poly[alkyl(aryl)oxysilanes] consisting of a dichlorosilane in an organic solvent as octane and a diol in 2,5-hexanedione is presented. It is believed that polymerization occurs near the interface in the dione phase. The products are low to intermediate in molecular weight. As the nature of silane is varied, the rate of polymer formation varies, the silane with the most electron-deficient silicon giving the greatest rate. Molecular weight is constant as diol is changed but varies when the silane is changed so that the silane with the most bulky substitutes will give polymer with the lowest molecular weight. The results are consistant with a S_N2 type reaction mechanism.     

Polymerization Mechanism of α-Linear Olefin

The density functional theory on the level of B3LYP/6-31G was empolyed to study the chain growth mechanism in polymerization process of α-linear olefin in TiCl₃/AlEt₂Cl catalytic system to synthesize drag reduction agent. Full parameter optimization without symmetryrestrictions for reactants, products, the possible transition states, and intermediates wascalculated. Vibration frequency was analyzed for all of stagnation points on the potential energy surface at the same theoretical level. The internal reaction coordinate was calculated from the transition states to reactants and products respectively. The results showed as flloes:(i) Coordination compounds were formed on the optimum configuration of TiCl₃/AlEt₂Cl.(ii) The transition states were formed. The energy di?erence between transition states and the coordination compounds was 40.687 kJ/mol. (iii) Double bond opened and Ti-C(4) bond fractured, and the polymerization was completed. The calculation results also showedthat the chain growth mechanism did not essentially change with the increase of carbon atom number of α-linear olefin. From the relationship between polymerization activation energy and carbon atom number of the α-linear olefin, it can be seen that the α-linear olefin monomers with 6-10 carbon atoms had low activation energy and wide range. It was optimum to synthesize drag reduction agent by polymerization.     

Kinetics and mechanism of the ring opening polymerization of (R,S)-β-butyrolactone initiated with dibutylmagnesium

Ring opening polymerization (ROP) of (R,S)-β-butyrolactone (BL) using dibutylmagnesium (Bu₂Mg) as initiator was investigated both in bulk and in solution. The synthetic poly-3-hydroxybutyrates (P3HB) were characterized by ¹H NMR, ¹³C NMR, FT-IR and GPC. Effects of molar ratio of initiator to monomer, reaction temperature and time on the monomer conversion and the polymer molecular weight and its distribution were discussed. The kinetics of the solution polymerization of BL was examined and showed a first order both in monomer concentration and initiator concentration. The end groups analysis suggested that the monomer inserted into the growing chain proceeding through the coordination-insertion mechanism based on the acyl-oxygen bond scission rather than the alkyl-oxygen bond cleavage of the BL ring. Furthermore, a possible mechanism for the initiation and propagation procedures of P3HB synthesized from BL with Bu₂Mg was proposed.     

Die Polymerisation von N-Vinylcarbazol in Gegenwart von Tetrabromkohlenstoff, 1. Mitt.: Der Einfluß von langwelligem UV

N-Vinylcarbazol (NVC) shows an extremely fast polymerization when irradiated for several minutes in a glass vessel at 30°C with long wave length UV in benzene solutions containing CBr₄. The conversion-time curves are sigmoid in character. The polymerization continues with its rate practically unchanged when the irradiation is stopped. Therefore termination reactions must be absent in this polymerization process which is shown to be cationic in mechanism. When a solution of CBr₄ in benzene is irradiated and the monomer is added after the irradiation has been stopped polymerization occurs likewise; its rate, however, is two orders of magnitude less than the maximum rates in the direct polymerization in the presence of CBr₄ and light. Here the conversion-time curves are linear. In both cases acidic products can be detected in the reaction systems. A reaction scheme is developed which attributes the initiation of polymerization by preirradiated CBr₄ solutions to the action of acidic decomposition products of CBr₄ (HBr). In the direct photopolymerization the monomer, probably in form of itsEDA-complex with CBr₄, participates in the initiation step or at least in the uptake of the photochemical energy, leading to a photochemically induced cationic polymerization. Based on this scheme an interpretation of the experimental results is given.     

Ni nanoparticles as electron-transfer mediators and NiSx as interfacial active sites for coordinative enhancement of H2-evolution performance of TiO2

The development of efficient photocatalytic H₂-evolution materials requires both rapid electron transfer and an effective interfacial catalysis reaction for H₂ production. In addition to the well-known noble metals, low-cost and earth-abundant non-noble metals can also act as electron-transfer mediators to modify photocatalysts. However, as almost all non-noble metals lack the interfacial catalytic active sites required for the H₂-evolution reaction, the enhancement of the photocatalytic performance is limited. Therefore, the development of new interfacial active sites on metal-modified photocatalysts is of considerable importance. In this study, to enhance the photocatalytic evolution of H₂ by Ni-modified TiO₂, the formation of NiS_x as interfacial active sites was promoted on the surface of Ni nanoparticles. Specifically, the co-modified TiO₂/Ni-NiS_x photocatalysts were prepared via a two-step process involving the photoinduced deposition of Ni on the TiO₂ surface and the subsequent formation of NiS_x on the Ni surface by a hydrothermal reaction method. It was found that the TiO₂/Ni-NiS_x photocatalysts exhibited enhanced photocatalytic H₂-evolution activity. In particular, TiO₂/Ni-NiS_x(30%) showed the highest photocatalytic rate (223.74 μmol h^?1), which was greater than those of TiO₂, TiO₂/Ni, and TiO₂/NiS_x by factors of 22.2, 8.0, and 2.2, respectively. The improved H₂-evolution performance of TiO₂/Ni-NiS_x could be attributed to the excellent synergistic effect of Ni and NiS_x, where Ni nanoparticles function as effective mediators to transfer electrons from the TiO₂ surface and NiS_x serves as interfacial active sites to capture H⁺ ions from solution and promote the interfacial H₂-evolution reaction. The synergistic effect of the non-noble metal cocatalyst and the interfacial active sites may provide new insights for the design of highly efficient photocatalytic materials.     

Mechanism and kinetics of polymerization of propylene in a microwave plasma

Flowing microwave plasma of propylene and propylene with argon was studied by mass spectrometry. Plasma composition was investigated as a function of external parameters such as pressure, argon/propylene ratio, and microwave-induced power. It was found that the propylene broke down to C₂H₂ and CH₄, or reacted further with propylene. Two main products, leading to the determination of three main chain reactions for the polymerization of propylene by ion-molecule interactions, were observed, namely, C₂H₂ and CH₄. These were the propylene, acetylene, and ethylene chain reactions. It was also found that the propylene disappeared in a pseudo-first-order reaction. Consequently an overall rate constant for the polymerization was determined (50 sec^–1 at 1 torr pressure for propylene plasma). This constant is found to be linearly dependent upon the propylene percent concentration, and nonlinearly dependent upon plasma pressure.Partly presented at the 157th meeting of the Electrochemical Society, St. Louis, Missouri, May 11–16, 1980.     

Effect of formaldehyde on the cationic polymerization of styrene

Polymerization of styrene has been carried out in the presence of formaldehyde at 30°C in benzene solution by using boron trifluoride etherate as a catalyst. The rate of polymerization in the initial stage was accelerated with addition of formaldehyde, while the steady-state rate of polymerization was retarded in the presence of formaldehyde. The acceleration for the rate of polymerization was found only in a short time from the beginning. The steady-state rate of polymerization followed the equation: where [C]₀ and [F]₀ are initial concentrations of catalyst and formaldehyde, [M] is the monomer concentration, and k₁, k₂, and k₃ are constants. It has been assumed that the chain-transfer reaction does not involve formaldehyde itself but rather the reaction products of formaldehyde, such as polystyrene having ethoxy or hydroxymethyl ends. The apparent chain-transfer constant for the added formaldehyde has been determined to be 1.63.     

Mechanism of phthalic anhydride formation in the oxidation of n-pentane on a vanadium-phosphorus oxide catalyst

The reaction paths of product formation in the partial oxidation of n-pentane on vanadium-phosphorus oxide (VPO) and VPO-Bi catalysts are considered. The condensed products of n-pentane oxidation were analyzed by chromatography-mass spectrometry, and the presence of C₄ rather than C₅ unsaturated hydrocarbons was detected. It was found that the concentration of phthalic anhydride in the products increased upon the addition of C₄ olefins and butadiene to the n-pentane-air reaction mixture. With the use of a system with two in-series reactors, it was found that the addition of butadiene to a flow of n-butane oxidation products (maleic anhydride, CO, and CO₂) resulted in the formation of phthalic anhydride. The oxidation of 1-butanol was studied, and butene and butadiene were found to be the primary products of reaction; at a higher temperature, maleic anhydride and then phthalic anhydride were formed. The experimental results supported the reaction scheme according to which the activation of n-pentane occurred with the elimination of a methyl group and the formation of C₄ unsaturated hydrocarbons. The oxidation of these latter led to the formation of maleic anhydride. The Diels-Alder reaction between maleic anhydride and C₄ unsaturated hydrocarbons is the main path of phthalic anhydride formation.     

Emulsifier-free polymerization of <Emphasis Type="Italic">n</Emphasis>-butyl acrylate involving trithiocarbonates based on oligomer acrylic acid

The effect of the chain length of oligomer acrylic acid obtained in the presence of a low-molecularmass trithiocarbonate and the position of trithiocarbonate fragment (within the chain or at the chain end) on the process of emulsion polymerization of n-butyl acrylate and characteristics of the resulting dispersions has been studied for the first time. It has been found that, when using an oligomer with trithiocarbonate group located within the chain in the emulsion polymerization of n-butyl acrylate in a wide range of monomer–water phase compositions, triblock copolymers self-organizing in aqueous medium to give stable particles with the core–shell structure are formed. Oligomers with M _n ～ (5–10) × 10³ are optimal for synthesis of stable dispersions. In this case, block copolymers with the controlled length of hydrophobic block and a rather narrow MWD may be obtained. Thin films formed from these copolymers retain the structure of the initial dispersions on solvent removal. If the trithiocarbonate group in the oligomer is located at the chain end, the main polymerization product is a diblock copolymer. In this case, the formation of polymer–monomer particles occurs during a longer period of time, the control of MWD is weakened, and the dispersions of particles lose the aggregative stability after thin film formation.     

Phenoxazine polymers: synthesis and structure

Phenoxazine polymers were obtained for the first time under conditions of chemical oxidative polymerization in aqueous alcohols and in an interphase process. The interphase process gave products with the higher molecular weight. Dependencies of the yields and degree of polymerization of phenoxazine from polymerization method, concentration of reactants, their ratio, reaction temperature and time, as well as chemical structures of the obtained polymers depending on the synthesis conditions, were studied. The polyphenoxazine chain growth is accomplished by the C-C-addition at the para-position of the phenyl rings with respect to nitrogen. Even when an excess of oxidant was used, the polyphenoxazine structure has only phenyleneamine units. The polymers obtained are amorphous and thermally stable.     

Study of the chain transfer reaction by hydrogen in the initial stage of propene polymerization

The chain transfer reaction by hydrogen in the initial stage of propene polymerization with MgCl₂-supported Ziegler catalyst was studied by means of the stopped-flow polymerization. The yield and molecular weight of polypropene produced in the initial stage were not affected by hydrogen. Thus, the method was successfully applied to find the region in which hydrogen does not act as a chain transfer reagent. On the other hand, a chain transfer reaction proceeded in the initial stage of polymerization by using Zn(C₂H₅)₂. Furthermore, when the catalyst was treated with Al(C₂H₅)₃ before polymerization, the molecular weight of the produced polymer was decreased by using hydrogen, indicating that it acted as a chain transfer agent for the catalyst modified by pre-treatment.     

Effect of enthalpy of polar modifiers interaction with n-butyllithium on the reaction enthalpy,kinetics and chain microstructure during anionic polymerization of 1,3-butadiene

The influence of interaction enthalpy (ΔH_MOD/BuLi) of μ, σ, σ+μ and σ-μ complexing polar modifiers with n-butyllithium on the 1,3-butadiene anionic polymerization enthalpy (ΔH_BD), polymerization reaction rate (k_p) and polybutadiene microstructure was studied. It has been found that enthalpy of interaction depends on complex type, molar ratio of polar modifier to n-butyllithium (MOD/BuLi) and temperature. For the first time it has been proven that with increasing ΔH_MOD/BuLi the content of 1,2 butadiene (vinyl) units in the chain increases individually for each complex type but the value of ΔH_BD decreases similarly for all complexes containing σ-donor groups, exhibiting linear nature. Since ΔH_MOD/BuLi controls the content of butadiene isomeric structures in the chain its value was compared with polymerization reaction rate, ranging from ∼46 to ∼5500 moL/L·min, and discussed on mechanistic level.     

Polyepichlorohydrin diols free of cyclics: Synthesis and characterization

Polymerization of epichlorohydrin (ECH) in the presence of diols, catalyzed by Lewis or protic acids, proceeds by activated monomer mechanism (AMM), i.e., by subsequent additions of protonated monomer molecules to the terminal hydroxyl groups of the growing chain. As opposed to the typical active chain end mechanism, side reactions, including cyclization, are strongly suppressed in the polymerization by AMM and well-defined linear product are obtained. It follows from kinetic considerations, that in order to achieve the high contribution of AMM, the reaction should be carried out at low instantaneous concentration of monomer, and this can be accomplished by slowly adding ECH to the reaction mixture. Using this approach, polyepichlorophydrin diols have been prepared in the M?_n ～ 2500 products with DP _n = [M]₀/[I]₀ can be obtained practically free of cyclic by-products with the yields approaching quantitative. Polyepichlorohydrin diols obtained by AM polymerization are strictly bifunctional, regular head-to-tail polymers containing mainly (≥ 95%) secondary hydroxyl and groups.     

Effect of monomer/nanoclay interaction on the kinetics of atom transfer radical homo- and copolymerization of styrene and methyl acrylate

Atom transfer radical homo- and copolymerization of styrene and methyl acrylate initiated with CCl₃-terminated poly(vinyl acetate) macroinitiator were performed at 90°C in the presence of nanoclay (Cloisite 30B). Controlled molecular weight characteristics of the reaction products were confirmed by GPC. It was shown that nanoclay slightly decreased the rate of styrene polymerization, while it significantly enhanced the rate of methyl acrylate polymerization and its copolymerization with styrene. The reactivity ratios of the monomers in the presence and in the absence of nanoclay were calculated (r _St = 1.002 ± 0.044, r _MA = 0.161 ± 0.018 by extended Kelen-Tudos method and r _St = 1.001 ± 0.038, r _MA = 0.163 ± 0.016 by Mao-Huglin method), confirming that the presence of nanoclay has no influence on monomer reactivity. The enhancement in the homopolymerization rate of methyl acrylate as well as its copolymerization rate with styrene was attributed to nanoclay effect on the dynamic equilibrium between active (macro)radicals and dormant species. Dipole moments of the monomers were successfully used to predict structure of the polymer/clay nanocomposites prepared via in situ polymerization.