Kinetic Identification of a Mechanism of Complex Plasma Chemical Reactions

Systems of differential rate equations characteristic for several basic types of plasma chemical reactions have been obtained. Every system permits one to reproduce a full kinetic picture of the reaction (kinetic curves of the starting, intermediate, and final compounds) and identify its mechanism by comparing this picture with the experimental kinetic pattern. The four important cases of a gas-phase plasma polymerization were considered in detail: radical propagating chain and stepwise recombination–activation, each having two different mechanisms of the death of plasma radicals. A comparison between the theoretical and experimental (mass spectrometry) kinetic patterns of six starting monomers and their low-molecular-weight products has established the chain mechanism predominating in all cases at the initial stages of the synthesis.     

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.     

Kinetics of the decay of nitroxyl radicals during polymerization of a complex of acrylamide with bismuth nitrate

Kinetics of the decay of nitroxyl radicals during spontaneous polymerization of complexes of acrylamide (AAm) with Bi^III nitrate has been studied by ESR. From a comparison of the experimental and calculated kinetic curves, the initiation rate constant of polymerization has been determined. The approach proposed is suitable for determining the main kinetic characteristics of other polymerizable nonparamagnetic AAm complexes with metal nitrates.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1572–1575, September, 1994.This work was carried out with the financial support of the Russian Foundation for Basic Research (Project No93-03-4162).     

A kinetic model for the growth of znte by metal organic chemical vapour deposition

A kinetic model for the metal organic chemical vapour deposition (MOCVD) growth of ZnTe is presented, taking into account the competitive adsorption of organometallic precursors. By assuming that diethylzinc (DEZn) and diethyltellurium (DETe) or di-isopropyltellurium (DIpTe) are adsorbed onto the surface by two sites, the model yields the growth rate as a function of the gas-phase concentrations of the constitutents and is corroborated by experimental results obtained by the MOCVD growth (at 400°C with DETe or 350°C with DIpTe), which shows asymmetric behaviour: for a given DETe or DIpTe pressure (10^?4 atm), the growth rate as a function of DEZn partial pressure passes through a maximum, whereas, at the same constant DEZn pressure, the growth rate increases monotonically when the DETe or DIpTe partial pressure increases     

Modeling of the Microwave Initiated Emulsion Polymerization of Styrene

The emulsion polymerization of styrene, activated by microwave irradiation and conductive heating, was modeled using the Predici^® simulation package of CiT. Microwave activated initiation was modeled as adding a second conventional free‐radical chemical initiator, whose concentration is given by the intensity of microwave irradiation, and its “decomposition” kinetic rate constant is related to the ratio of monomer concentration to the rate of absorbed radiation. Most of the kinetic rate constants and model parameters used in the model were taken from the literature, in order to avoid unnecessary parameter estimation procedures. Model predictions of conversion, number and weight average molecular weights, for microwave and thermally activated systems, agree well with the experimental data reported in the literature, including experimental data previously reported by our own group.     

Ti－Mg系载体催化剂乙烯加氢预聚合对乙烯气相聚合的影响

Ｔｉ－Ｍｇ系载体催化剂乙烯加氢预聚合对乙烯气相聚合的影响李悦，林尚安（东莞理工学院应用化学系，东莞，５１１７００）（中山大学高分子研究所）关键词Ｚｉｅｇｌｅｒ－Ｎａｔｔａ催化剂．预聚合催化剂．乙烯气相聚合乙烯聚合特别是气相聚合十分注意聚合初活性的调节...     

A discussion on the kinetic behavior of Ziegler–Natta ethylene polymerization at early moments of the reaction via modeling

The gas-phase ethylene polymerizations with SiO₂-supported Ziegler–Natta (ZN) catalyst at early moments of reaction is modeled. The experimental data used in this work show that at initial stages of the polymerization there is a sharp reduction in the reaction rate and a sharp rise in molecular weight. In the modeling, multi-active sites assumption and diffusion limitations inside the particle are studied. Energy balance to calculate the temperature at early moment is applied. Kinetic model including initiation, propagation, chain transfers and active site deactivation steps are used to predict the reaction rate and molecular weights. Polymeric flow model (PFM) is applied for single particle model (SPM). The results show two distinct regions. First region with sharp gradient for reaction rate and molecular weights and then, shortly there is a smooth region in which the changes in rate and molecular weights are slow. To fit this sharp gradient followed by a nearly steady state behavior two types of active sites are necessary. A group of highly active sites which deactivated soon and the active sites with lower activity and relatively long-lasting.     

Modeling stable free-radical polymerization

A kinetic model has been developed for stable free-radical polymerization (SFRP) processes by using the method of moments. This model predicts monomer conversion, number-average molecular weight, and polydispersity of molecular weight distribution. The effects of the concentrations of initiator, stable radical, and monomer, as well as the rate constants of initiation, propagation, termination, transfer, and the equilibrium constant between active and dormant species, are systematically investigated by using this model. It is shown that the ideal living-radical polymerization having a linear relationship between number-average molecular weight and conversion and a polydispersity close to unity is the result of fast initiation, slow propagation, absence of radical termination, and a high level of dormant species. Increasing stable radical concentration helps to reduce polydispersity but also decreases polymerization rate. Thermal initiation significantly broadens molecular weight distribution. Without the formation of dormant species, the model predicts a conventional free-radical polymerization. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 2692–2704, 1999     

Living free‐radical polymerization of styrene under a constant source of γ radiation

Living polymerization of styrene was observed using γ radiation as a source of initiation and 1‐phenylethyl phenyldithioacetate as a reversible addition–fragmentation chain transfer (RAFT) agent. The γ radiation had little or no detrimental effect on the RAFT agent, with the molecular weight of the polymer increasing linearly with conversion (up to the maximum measured conversions of 30%). The polymerization had kinetics (polym.) consistent with those of a living polymerization (first order in monomer) and proportional to the square root of the radiation‐dose rate. This initiation technique may facilitate the grafting of narrow polydispersity, well‐defined polymers onto existing polymer surfaces as well as allow a wealth of kinetic experiments using the constant radical flux generated by γ radiation. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 40: 19–25, 2002     

A copper‐based reverse atom‐transfer radical polymerization process for the living radical polymerization of polyacrylonitrile

The reverse atom‐transfer radical polymerization (RATRP) technique using CuCl₂/2,2′‐bipyridine (bipy) complex as a catalyst was applied to the living radical polymerization of acrylonitrile (AN). A hexasubstituted ethane thermal iniferter, diethyl 2,3‐dicyano‐2,3‐diphenylsuccinate (DCDPS), was firstly used as the initiator in this copper‐based RATRP initiation system. A CuCl₂ to bipy ratio of 0.5 not only gives the best control of molecular weight and its distribution, but also provides rather rapid reaction rate. The rate of polymerization increases with increasing the polymerization temperature, and the apparent activation energy was calculated to be 57.4 kJ mol^?1. Because the polymers obtained were end‐functionalized by chlorine atoms, they were used as macroinitiators to proceed the chain extension polymerization in the presence of CuCl/bipy catalyst system via a conventional ATRP process. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 226–231, 2006     

Semibatch Atom Transfer Radical Copolymerization of Styrene and Butyl Acrylate

Summary: Batch and semibatch butyl acrylate (BA) polymerizations are carried out using a heterogeneous atom transfer radical polymerization (ATRP) catalyst system, with excellent molecular weight (MW) control maintained at temperatures below 80 °C. A kinetic model, using rate coefficients from literature and catalyst solubility data from this study, provides a good representation of the experimental results, after modifying the model to account for the decrease in rate caused by intramolecular chain transfer. It is also demonstrated experimentally that well-defined random, gradient, and block styrene/BA copolymers can be synthesized by manipulating monomer feed profiles in the ATRP semibatch process.     

Modeling of Ethylene Polymerization Kinetics over Supported Chromium Oxide Catalysts

Summary: Silica supported chromium oxide catalysts have been used for many years to manufacture polyethylene and they still account for more than 50% of world production of high‐density polyethylene. Along with its commercial success, the catalytic mechanism and polymerization kinetics of silica supported chromium oxide catalysts have been the subject of intense research. However, there is a lack of modeling effort for the quantitative prediction of polymerization rate and polymer molecular weight properties. The chromium oxide catalyzed ethylene polymerization is often characterized by the presence of an induction period followed by a steady increase in polymerization rate. The molecular weight distribution is also quite broad. In this paper, a two‐site kinetic model is developed for the modeling of ethylene polymerization over supported chromium oxide catalyst. To model the induction period, it is proposed that divalent chromium sites are deactivated by catalyst poison and the reactivation of the deactivated chromium sites is slow and rate controlling. To model the molecular weight distribution broadening, each active chromium site is assumed to have different monomer chain transfer ability. The experimental data of semibatch liquid slurry polymerization of ethylene is compared with the model simulations and a quite satisfactory agreement has been obtained for the polymerization conditions employed.

Polymerization rates at different reaction temperatures: symbols – data, lines – model simulations.     

钇系超导体有机硅保护膜的磁控等离子体聚合

A new method of deposition of organic silicon film by magnetic-controlling plasma polymerization was used to protect Y-Ba-Cu-O superconductor from corrosion. The deposition rate of plasma polymer film with magnetic-controlling is 20 times over that without magnetic-controlling. The relation between the deposition rate of film and the process factors of magnetic-controlling plasma were studied. The Y-Ba-Cu-O superconductor covered with organic silicon film was formed by magnetic-controlling plasma polymerization had been protected from corrosion in water over 48 hours.     

Effects of Cathode and Anode on Deposition of Trimethylsilane in Glow Discharge

DC cathodic polymerization of trimethylsilane (TMS) was carried out in plasma reactors with and without using anode assembly. In DC cathodic polymerization, the TMS plasma polymers are mainly deposited on the cathode (substrate) surface. As a result, fast deposition of TMS plasma polymers was easily achieved in DC cathodic polymerization as compared with AF or RF plasma polymerization. DC cathodic polymerization without using anode assembly has its advantageous features that the size and number of substrates (as cathodes) are not restricted by the size and the location of anode assembly. It was found that the maximum deposition rate on the cathode surfaces was obtained without anode assembly. The DC cathodic polymerization of TMS was conducted also in a large volume reactor with multiple cathodes (substrates). The same deposition mechanisms for DC cathodic polymerization with a single cathode also apply to the multiple cathodes. Uniform deposition on each cathode could be obtained with appropriate spacing of multiple cathodes and by adjusting the operational parameters, which are based on the current density and the system pressure.     

双金属催化环氧化物聚合动力学研究

研究了双金属氰化络合催化剂DMC催化环氧丙烷聚合的动力学 .用测定反应过程体系压力变化来决定聚合的起始速率 ,发现聚合反应速率正比于催化剂用量C ,单体浓度M的平方 .该实验规律可以从单体参与链引发的动力学特点解释 .考察了温度对聚合反应速率的影响并求得了表观活化能为 5 9 1kJ·mol- 1 ,该值与环氧聚合的卟啉铝、稀土络合物等催化体系接近 .     

Controlled/“living” atom transfer radical polymerization of methyl methacrylate in the synthesis of triblock copolymers from a poly(oxyethylene) macroinitiator

Atom transfer radical polymerization of methyl methacrylate initiated by a poly(oxyethylene) macroinitiator by the esterification of PEG 1500 with 2-chloro propionyl chloride was synthesized. These polymerization proceeds both in bulk and solution with a quantitative initiation efficiency, leading to A-B-A triblock copolymers. The macroinitiators and their block copolymers were characterized by FT-IR, FT-NMR and GPC analyses. In bulk polymerization, the kinetic study showed that the relationship between ln[M]₀/[M] vs time was linear showing that there is a constant concentration of active species throughout the polymerization and follow the first order kinetics with respect to monomer. Moreover, the experimental molecular weight of the block copolymers increased linearly with the monomer conversion and the polydispersity index remained between 1.3 and 1.5 throughout the polymerization. No formation of homo poly(methyl methacrylate) could also be detected, and all this confirms that the bulk polymerization proceeds in a controlled/“living” manner.     

Kinetic and mechanistic study of the quasiliving cationic polymerization of styrene with the 2-phenyl-2-propanol/AlCl3 · OBu2 initiating system

The cationic polymerization of styrene with the 2-phenyl-2-propanol (CumOH)/AlCl₃ · OBu₂ initiating system at various dibutyl ether concentrations in a mixture of 1,2-dichloroethane and n-hexane (55:45 v/v) at −15 °C was investigated. The experimental results showed that an increase in dibutyl ether concentration leads to a noticeable decrease in the polymerization rate as well as to the more controlled polymerization in terms of molecular weight (M_n) and molecular weight distribution (MWD) evolutions. The kinetic investigation revealed that the polymerization proceeds in two stages. The first stage is characterized by high polymerization rate and slow initiation relative to propagation. During this stage molecular weight decreases or does not change and MWD increases with conversion. In the second stage considerably slower quasiliving polymerization of styrene occurs. The quasiliving nature of the styrene polymerization by the CumOH/AlCl₃ · OBu₂ system is proved and mechanistic scheme of the polymerization is proposed.     

A Two‐Step Interval and Modified Rosenbrock Method for Kinetic Parameter Estimation in Copolymerization Systems: A Robust and Reliable Approach

Summary: The kinetics of solution free radical copolymerization of isobutyl methacrylate (i‐BMA) and lauryl methacrylate (LMA) in benzene, initiated with 2,2‐azoisobutyronitrile (AIBN) were studied at different monomer feed compositions at low conversion levels. In order to avoid the complications of copolymerization kinetics, the pseudo‐kinetic rate constant method was applied in constant and variable volume polymerization systems. A two‐step procedure based on interval analysis and the modified Rosenbrock method was used to estimate the kinetic parameters of copolymerization. In the first step, initiation, coupled propagation‐termination and transfer rate parameters were determined from steady state kinetic equations using interval analysis. Since the objective function is non‐linear, non‐convex and has multiple local optima, a robust computational technique, based on the Interval Newton/Generalized Bisection (IN/GB) algorithm, was developed to solve this set of non‐linear algebraic equations. This method was used with mathematical and computational guarantees of certainty to find the global optimum. In the second step, the system of mole balance, population balance and moment equations, which are highly stiff ordinary differential equations, were discritized and solved by the modified Rosenbrock method. The results of the first computational step were inserted as an active or equality constraint in the second step to calculate the individual elementary rate parameters of the reaction. Statistical analysis indicated that the copolymer composition is well described by the terminal unit model (TUM), but the implicit penultimate unit effect (IPUE) model of Fukuda and coworkers is more suitable for describing the rate data. In contrast to most previously studied systems, it was found that propagation and coupled rate parameters are greater than those predicted by the TUM.

Variation of number average molecular weight of the copolymer in polymerization system for various initial monomer feed compositions at different reaction times (solid lines are computed results).     

Effect of temperature on styrene emulsion polymerization in the presence of sodium dodecyl sulfate. II

The batch emulsion polymerization kinetics of styrene initiated by a water‐soluble peroxodisulfate at different temperatures in the presence of sodium dodecyl sulfate was investigated. The curves of the polymerization rate versus conversion show two distinct nonstationary‐rate intervals and a shoulder occurring at a high conversion, whereas the stationary‐rate interval is very short. The nonstationary‐state polymerization is discussed in terms of the long‐term particle‐nucleation period, the additional formation of radicals by thermal initiation, the depressed monomer‐droplet degradation, the elimination of charged radicals through aqueous‐phase termination, the relatively narrow particle‐size distribution and constant polydispersity index throughout the reaction, and a mixed mode of continuous particle nucleation. The maximum rate of polymerization (or the number of polymer particles nucleated) is proportional to the rate of initiation to the 0.27 power, which indicates lower nucleation efficiency as compared to classical emulsion polymerization. The low activation energy of polymerization is attributed to the small barrier for the entering radicals. The overall activation energy was controlled by the initiation and propagation steps. The high ratio of the absorption rate of radicals by latex particles to the formation rate of radicals in water can be attributed to the efficient entry of uncharged radicals and the additional formation of radicals by thermally induced initiation. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 1477–1486, 2000     

Catalytic effect of ionic liquids in the Cu2O/2,2′‐bipyridine catalyzed living radical polymerization of methyl methacrylate initiated with arenesulfonyl chlorides

The effect of 1‐butyl‐3‐methylimidazolium hexafluorophosphate ionic liquid on the living radical polymerization of methyl methacrylate initiated with arenesulfonyl chlorides and catalyzed by the self‐regulated Cu₂O/2,2′‐bipyridine catalyst was investigated. A dramatic acceleration of the living radical polymerization of methyl methacrylate in this ionic liquid was discovered. This accelerated living radical polymerization maintained an initiation efficiency of 100%, eliminated the induction period of this catalyst, and produced poly(methyl methacrylate) with molecular weight distribution of 1.1 and perfect bifunctional chain‐ends. The kinetic analysis of the living radical polymerization in the presence of ionic liquid demonstrated a rate constant of propagation that follows an almost first order of reaction on the ionic liquid concentration and therefore, the ionic liquid exhibits catalytic effect. The catalytic effect of the ionic liquid facilitated the reduction of the catalyst concentration from stoichiometric to catalytic and allowed the decrease of the polymerization temperature from 80 to 22 °C. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 5609–5619, 2005