Controllable fabrication of porous free-standing polypyrrole films via a gas phase polymerization

A facile gas phase polymerization method has been proposed in this work to fabricate porous free-standing polypyrrole (PPy) films. In the presence of pyrrole vapor, the films are obtained in the gas/water interface spontaneously through the interface polymerization with the oxidant of FeCl(3) in the water. Both the thickness of the film and the size of the pores could be controlled by adjusting the concentrations of the oxidant and the reaction time. The as-prepared PPy films exhibited a superhydrophilic behavior due to its composition and porous structures. We have demonstrated a possible formation mechanism for the porous free-standing PPy films. This gas phase polymerization is shown to be readily scalable to prepare large area of PPy films.     

Influence of diosgenin structure on the polymerization kinetics of acrylamide: An experimental and theoretical approach

The acrylamide polymerization in presence of diosgenin has been investigated by experimental and theoretical methods. NMR spectroscopy shows the absence of copolymerization. Viscosimetric and dilatometric experiments support the occurrence of transfer reactions that retard the polymerization. The mechanism was studied at the MPWB1K/6-31G(d,p)//B3LYP/6-31G(d,p) level of theory. Transfer, homopropagation, copolymerization and reinitiation reactions were considered either in gas or solution phase. According to results, the retardation seems to be originated by the formation of an allylic radical in the ring B of diosgenin that reinitiates acrylamide polymerization at slow rate.     

Early stages of styrene-isoprene copolymerization in gas phase clusters probed by resonance enhanced multiphoton ionization

We present direct evidence for the formation of the covalent bonded styrene (isoprene)(2) oligomer and the isoprene dimer ions following resonance ionization of the gas phase styrene-isoprene binary clusters. The application of resonance ionization to study polymerization reactions in clusters provides new information on the structure and mechanism of formation of the early stages of polymerization and holds considerable promise for the discovery of new initiation mechanisms and for the development of novel materials with unique properties.     

A Self‐Supporting Strategy for Gas‐Phase and Slurry‐Phase Ethylene Polymerization using Late‐Transition‐Metal Catalysts

The polyolefin industry is dominated by gas‐phase and slurry‐phase polymerization using heterogeneous catalysts. In contrast, academic research is focused on homogeneous systems, especially for late‐transition‐metal catalysts. The heterogenization of homogeneous catalysts is a general strategy to provide catalyst solutions for existing industrial polyolefin synthesis. Herein, we report an alternative, potentially general strategy for using homogeneous late‐transition‐metal catalysts in gas‐phase and slurry‐phase polymerization. In this self‐supporting strategy, catalysts with moderate chain‐walking capabilities produced porous polymer supports during gas‐phase ethylene polymerization. Chain walking, in which the metal center can move up and down the polymer chain during polymerization, ensures that the metal center can travel along the polymer chain to find suitable sites for ethylene enchainment. This strategy enables simple heterogenization of catalysts on solid supports for slurry‐phase polymerization. Most importantly, various branched ultra‐high‐molecular‐weight polyethylenes can be prepared under various polymerization conditions with proper catalyst selection.     

用高效SiO2载体催化剂进行乙烯气相聚合

使用球形ＳｉＯ２负载ＭｇＣｌ２－ＴｉＣｌ４高活性催化剂进行乙烯气相聚合，考察了催化剂制备条件和添加剂对催化剂的组成、催化活性以及聚合表观动力学的影响．结果表明，ＳｉＯ２热处理温度和所用的醇对Ｍｇ和Ｔｉ的负载量及乙烯聚合活性有明显的影响．催化剂制备中添加Ｌｅｗｉｓ酸ＳｉＣｌ４或ＡｌＥｔ２Ｃｌ能大幅度提高催化剂的活性，其中以ＳｉＣｌ４的效果最为明显．随着ＳｉＣｌ４用量的增加，乙烯气相聚合的活性显著提高，聚合速度随时间变化由渐升平稳型转变为衰减型     

Vapor phase composition and radical polymerization—how the gas phase influences the kinetics of heterophase polymerization

The outcome of radical styrene heterophase polymerization depends strongly on the composition of the gas phase. Data of a comprehensive experimental study show that the effect of the gas phase is quite a complex one and strongly influenced by the nature of the gas, the homogeneity or heterogeneity of the polymerization system, and the kind of initiator. Evidence is presented that the influence of air goes beyond the simple action of oxygen which can cause deceleration or acceleration of the reaction. The experimental results show that the optimum polymerization conditions are obtained in the absence of any foreign gas.     

The effect of frequency on the plasma polymerization of ethane

The plasma polymerization of ethane has been studied in the frequency range of from 50 Hz to 13.56 MHz. The rate of polymer deposition is strongly dependent on frequency, with significantly higher rates being observed at frequencies below 6 MHz. The effects of frequency can be interpreted in terms of a mechanism that assumes that polymer is formed by the reaction of surface free radicals, created by the bombardment of the growing polymer by charged species, with gas phase free radicals, formed by collisions of energetic electrons with monomer molecules.     

Dissipative particle dynamics simulation study on the binary mixture phase separation coupled with polymerization

The influence of polymerization on the phase separation of binary immiscible mixtures has been investigated by the dissipative particle dynamics simulations in two dimensions. During polymerization, the bulk viscosity increases, which consequently slows down the spinodal decomposition process. The domain size growth is monitored in the simulations. The absence of 23 exponent for inertial hydrodynamic mechanism clearly reflects the suppressing effect of polymerization on the phase separation. Due to the increasing viscosity, the individual phase may be trapped in a metastable stage instead of the lamellar morphology identified for symmetric mixtures. Moreover, the polymerization induced phase separation in the binary miscible mixture has been studied. The domain growth is strongly dependent on the polymerization probability, which is naturally related to the activation energy for polymerization. The observed complex phase separation behavior is attributed to the interplay between the increasing thermodynamic driving force for phase separation and the increasing viscosity that suppresses phase separation as the polymerization proceeds.     

Crystallization during polymerization of poly-p-xylylene

Crystallization during polymerization of p-xylylene from the gas phase has been studied between 200 and ?196°C. From room temperature to ?17°C the polymer crystal morphology changes in that the crystallinity decreases. In this range the process is thought to be of the successive polymerization and crystallization type. The morphology is in agreement with this mechanism, of the folded-chain β-polymorph type with proper epitactic orientation of the chains with respect to the support surface. At ?78°C an intermediate, poorly crystallized polymer results. At 196°C the reaction is most likely of the simultaneous polymerization and crystallization type. The morphology is, in agreement with the changed mechanism, of a metastable, irregularly folded β-polymorph type with no orientation of the chains relative to the support surface. No significant changes in molecular weight were observed in the polymers produced between 26 and ?196°C.     

Gas Phase Polymerization of Ethylene with Supported Titanium-Nickel Catalysts

A new ditransition-metal catalyst system TiCl4-NiCl2/MgCl2-SiO2/AlR3 was prepared.Gas phase polymerization of ethylene with the catalysts has been studied.The kinetic curves of gas phase polymerization showed a decline.The catalystic efficiency and polymerization reaction rates have a optimum value when Ni content of the catalysts was 12.5%(mol).The products obtained are branched polyethylene.     

A Mechanisms and Kinetics Study of Polymeric Thin-Film Deposition in Glow Discharge

Polymeric thin-film deposition in a capacitively coupled rf glow discharge of styrene has been investigated. A kinetic scheme for the polymerization was proposed in which initiation of monomers by electron impact was followed by propagation and termination as in conventional polymerization, the initiation rate constant being a function of electron temperature alone. Four mechanism models were examined, depending on where each reaction step takes place: in the gas phase or on the substrate. Free-radical polymerization was assumed. Experiments were carried out at pressures ranging from 0.25 to 1.05 Torr and at voltages and currents that yielded cold and stable discharges. Substrate temperature was controlled. Deposition rate was determined by weighing. A regression program was used in addition to experimental tests in which substrate temperature was varied. The best approximation to the plasma polymer deposition process was found to be the following model: monomers are activated in the gas phase by electron bombardment and subsequently diffuse to the substrate where they propagate and terminate, adsorption of monomers on the substrate playing an important role. A rate expression relating polymer film deposition rate to the experimental variables is presented.     

Influence of the Luminous Gas Phase into Butane Plasma Polymerization in a Closed Reactor System

High Energy Chemistry - This study investigated the plasma polymerization process of butane in a closed radio frequency plasma reactor system. Optical emission spectra of the luminous gas phase...     

四氟乙烯等离子体聚合的研究——Ⅱ.四氟乙烯等离子体聚合的反应历程

<正> 在前报,已应用ESCA等方法研究了辉光区和非辉光区等离子体聚四氟乙烯(PPTFE)淀积膜的结构。鉴于等离子体聚合反应的复杂性,前人对等离子体聚合反应机理争论较大,争论焦点集中在反应的活性种是离子还是自由基以及反应的地点这两个问题上,本工作在前报工作的基础上,进一步应用ESR检测出等离子体气体流出物的冷凝物中含有大量自由基,为证实等离子体聚合的自由基反应历程提供了新依据;还采用GC-MS表征了气体冷凝物的结构。比仅用MS分析气相产物有较大优点。综合这些实验结果,为推测四氟乙烯等离子体聚合反应历程奠定了一定的基础。     

Gas Phase Polymerisation of Ethylene with Supported Titanium-Nickel Catalysts

Olefins gas phase polymerization uses generally supported titanium catalyst systems inindustrial production. The polymerization of olefins with late transition metal catalysthas recently attracted considerable interestl-2. The new catalyst family shares many ofthe advantages of metallocene catalysts in terms of activity and control of polymerproperties and, in addition, the new catalysts yield homopolymer of ethylene with veryhigh branching degrees and branching degree can be controlled.A new …     

Heterogeneous polymer systems. IV. Mechanism of rubber particle formation in rubber-modified vinyl polymers

A mechanism for the formation of rubber particles in the polymerization of solutions of rubber in vinyl monomers is presented. A polymeric oil-in-oil emulsion is formed in the first phase of the polymerization. This polymeric oil-in-oil emulsion is transtormed into a solid dispersion of rubber in vinyl polymer in the second phase of the polymerization. A phase inversion takes place in the emulsion in the first phase of the polymerization. Rubber solution droplets are formed at the phase inversion point. These droplets harden as the polymerization proceeds and are gradually transformed into the solid, crosslinked rubber particles of the final polymer.     

Kinetic study of gas phase olefin polymerization with a TiCl4/MgCl2 catalyst. II. Kinetic parameter estimation and model building

Monomer transport and polymerization kinetics are two key phenomena in olefin polymerization with heterogeneous transition metal catalysts. To have a better understanding of these interrelated kinetics and diffusion phenomena, a quantitative calculation of the monomer diffusion directly from experimental study is essential. In this work, a novel temperature-perturbation technique is developed to systematically study the kinetic and diffusion limitations in catalyzed gas phase olefin polymerization. A physical model of the particle growth mechanism as well as its mathematical representation is presented and the diffusion limitations occurring in the system at high temperature are characterized and quantitatively analyzed. Finally, the practical implications of the results of this study on the operation of industrial scale polyolefin reactors are examined. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 2075-2096, 1997     

A Single-Gallery Model for the In Situ Production of Polyethylene-Clay Nanocomposites

Polyolefin-clay nanocomposites are finding many new applications because of their improved properties, such as high modulus, elevated scratch resistance and low gas permeability. Currently, these composites are produced by melt blending organically modified clay with polyolefins. The most challenging step in this process is the intercalation and exfoliation of the clay to produce a homogenously dispersed phase at the nanoscale. A promising alternative to melt blending is in-situ polymerization, where the polymer is produced between the clay layers in the polymerization reactor. In-situ polymerization of olefins with metallocene catalysts supported on clay can produce nanocomposites using conventional polymerization reactors, provided that the clay can be used as a support for the olefin polymerization catalyst. In this approach, the clay fulfills the functions of catalyst support and dispersed phase in the final nanocomposite. In this work, a mathematical model describing particle growth during in-situ polymerization of ethylene with a metallocene catalyst supported on clay will be discussed. The model expands the approach of the multi-grain model used in heterogeneous olefin polymerization to account for the layered structure of clays.     

Novel molecularly hybridized polyethylene/silica composite materials: Polymerization of ethylene with supported titanocenes by mesoporous silicates

A novel molecularly hybridized polyethylene/silica composite thin film was obtained by the gas‐phase polymerization of ethylene with a titanocene‐mounted mesoporous silica layer on a mica plate with mesoscopic pores arranged on the film surface. However, the use of titanocene‐mounted hexagonal domains of mesoporous silica on a glass plate for the gas‐phase polymerization of ethylene resulted in the formation of an islanded polyethylene/silica hybridized material. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 4821–4825, 2000     

Kinetics of heterogeneous free-radical polymerization of vinylidene chloride

Poly(vinylidene chloride) precipitates as a crystalline phase during the polymerization reaction. Under the conditions studied, this phase is made up of complex particles with a lamellar substructure. The detailed morphology is very sensitive to reaction medium. The morphology developed by particles formed during polymerization of vinylidene chloride in dioxane suggests a mechanism of polymerization followed by crystallization. The morphology observed in mass polymerization suggests that both processes occurs simultaneously. Kinetic data, however, suggest a solid-phase reaction mechanism for both cases. The results are analyzed by comparison with a model that takes into account the solid-phase morphology. The theoretical analysis is consistent with experimental results if it is assumed that polymerization occurs on the edges of the lamellar crystals.     

Characterization of the changes in the initial morphology for MgCl2-supported Ziegler-Natta polymerization catalysts

Recently considerable detail has become available on the initial morphology and the morphological changes that occur for silica based Cr catalysts for ethylene polymerization. These catalysts are produced as a dry powder and may be employed either in gas phase or in slurry processes. MgCl₂-supported Ziegler-Natta polymerization catalysts are often prepared and employed as slurries. They usually are never dried and thus few studies have employed the spectra of physical techniques common to the characterization of pore structure. In the current study, we have carefully removed the solvent for both ball-milled and precipitated MgCl₂-supported catalysts. These catalysts are characterized by physical sorption, mercury porosimetry, and electron microscopy both as prepared and during the initial stages of polymerization (to ～ 100 g of polymer/g of catalyst). We find that the initial catalyst may be represented by a complex agglomerate of small crystallites as contrasted with the branched pore network found in Cr/silica catalysts. As a result, it is concluded that the initial fragmentation of the MgCl₂ based systems is more uniform as contrasted with the progressive fragmentation of the silica-based system. This fragmentation mechanism facilitates the retention of greater polymer/catalyst surface during the initial stages of the polymerization. © 1992 John Wiley & Sons, Inc.