Termination Rates in Free Radical Copolymerizations

The rates of free radical copolymerizations at given rates of initiation can be analyzed ideally in terms of monomer feed concentrations and reactivity ratios, propagation rate constants for homopolymerizations of the particular monomers, and an overall rate constant for termination during copolymerization. This model, which is due to Atherton and North, can account for the effects of initiator concentration and viscosity of the polymerization medium on copolymerization rates.

This article reports an empirical formulation for the overall termination rate constant in terms of monomer concentrations and reactivity ratios and a cross-termination factor. The new model accounts for experimental data in the styrene-methyl methacrylate system in which polarity differences between unlike radicals may result in enhanced termination rates. It also predicts observed copolymerization rates of methyl methacrylate-vinyl acetate and styrene-α-methylstyrene mixtures in which polarity effects are absent. The cross-termination factor may be approximated from reactivity ratio data for predictive purposes.     

Studies in Cyclocopolymerization. IX. A Systematic Kinetic Study on the Cyclocopolymerization of Vinyl Ethers with Maleic Anhydride in Different Solvents

Abstract

The kinetics of the AIBN-initiated copolymerization of divinyl ether (DVE) and ethyl vinyl ether (EVE) with maleic anhydride (MA) was extensively studied in seven different solvents. The yield at 100% conversion as a function of the feed composition when the total monomer concentration is kept constant gave a confirmation of the composition of these copolymers: DVE/MA=½ and EVE/MA=1/1. The study of the initial rate as a function of the feed composition made it possible to determine the relative values of the different propagation rate constants consistent with a mechanism by successive and selective additions: in the EVE-MA system, the addition of EVE is slower than the addition of MA; in the DVE-MA system, the addition of DVE is slower than the addition of the first MA molecule, while the addition of the second MA molecule is slower than the first one. The study of the dependence of the monomer concentration, of the AIBN concentration, and of the efficiency of the initiator, on the rate of polymerization, shows finally that the true order of the monomer concentration is close to 1 while its apparent order varies from 1 to 2. From all the kinetic data it was observed that the mechanism of these co polymerizations can be explained without reliving upon the concept of participation of the charge-transfer complex formed between the monomers. However, participation of the complex in a competing mechanism with the above cannot be completely excluded.     

Effect of reaction medium on the radical polymerization and copolymerization of potassium and sodium p-styrenesulphonate

The kinetics of the homogeneous free radical polymerization of potassium p-styrenesulphonate and sodium p-styrenesulphonate (SSS) in water-salt, water-dioxane, water-dimethyl sulphoxide (DMSO), DMSO—dioxane mixtures and copolymerization of SSS with acrylamide in water-salt and water-DMSO mixtures have been investigated. The overall rate of the process, the kinetic orders with respect to monomer and initiator, overall activation energy and also the properties of the resulting polymers (molecular weight, copolymer composition and compositional inhomogeneity) depend on the nature of the reaction medium. It is mainly connected with the influence of ionic strength (due to varying ionogenic monomer concentration, addition of salts and also the change of the conversion degree) and with the influence of the polarity of solvent on the rate constants for propagation and termination. The chemical and physical characteristic of the reaction mainly influence parameters of the electrostatic interactions in the system “macroradical-counterions-anions of monomer”. This leads to conformational variation of polymer chains and influences the reactivities of growing macroradicals and ionogenic monomers in polymerization and copolymerization. Data on conductivity and viscometric measurements confirmed the dependence of the conformation of polymer and copolymer macromolecules upon the composition of the medium.     

Free‐Radical Frontal Copolymerization: The Dependence of the Front Velocity on the Monomer Feed Composition and Reactivity Ratios

Frontal copolymerization is a process in which a spatially localized reaction zone propagates into a mixture of two monomers, converting them into a copolymer. In the simplest case of free‐radical copolymerization, a mixture of monomers and initiator is placed into a test tube. Reaction is initiated at one end of the tube, and a self‐sustained thermal wave, in which chemical conversion occurs, develops and propagates through the tube. We develop a mathematical model of the frontal copolymerization process and analytically determine the structure of the polymerization wave, the propagation velocity, maximum temperature, and degree of conversion of the monomers. Specifically, we examine their dependence on reactivity ratios as well as other kinetic parameters, monomer feed composition, and exothermicity of the reactions. Our analytic results are in good quantitative agreement with both direct numerical simulations of the model and experimental data, which are also presented in the paper.

Dependence of front velocity on monomer feed composition for different heat release parameters.     

60Co-initiated copolymerization of styrene with vinyl acetate

The kinetic behavior of the ⁶⁰Co-initiated copolymerization at 25°C of styrene with vinyl acetate at 1100 and 2000 rad/hr was studied. As in the case of thermal and photochemical copolymerizations of these monomers, the growing chains are particularly rich in styrene units, and the overall rate is affected by a diluent effect due to the vinyl acetate monomer. However, in the case of the radiation copolymerization, this effect is partially counterbalanced by an increase of the initiation rate with the vinyl acetate concentration; the polymerization rate curve shows a maximum at a vinyl acetate molar fraction of 0.25. This effect is due to the very different free radical yields of these two monomers. The experimental results may be understood on the basis of a kinetic scheme which involves an energy transfer process from the excited vinyl acetate molecules to the styrene monomer and a termination reaction of the growing chains by very short styrene radicals when the mixture is rich in vinyl acetate.     

Free radical terpolymerization of three non‐homopolymerizable monomers, 1 Kinetic scheme

In previous papers two models were proposed which describe the terpolymerization of non‐homopolymerizable donor and acceptor monomers. The first one is based on the terminal model considering only the propagation reactions of the free monomers. The second one is the complex model considering only the reactions of charge‐transfer complexes. This paper describes a new kinetic scheme involving the participation of both the free monomers and the charge‐transfer complexes. Quantitative treatment of the overall polymerization rate by this new kinetic scheme allows to evaluate the degree of the participation of the free monomers and the charge‐transfer complexes. For the first time therefore it is possible to determine quantitatively the influence of charge‐transfer complexes on the free radical terpolymerization of non‐homopolymerizable monomers.     

Mechanism of alternating copolymerization of methyl methacrylate with styrene in the presence of diethylaluminum chloride

A kinetic study of the propagation mechanism of the alternating copolymerization of styrene (St) with methyl methacrylate (MMA) in the presence of a complexing agent (diethylaluminum chloride, DEAC) in bulk and in tetrachloroethylene solutions at a molar ratio DEAC/MMA = 0.5 has been carried out. It has been shown that the copolymerization is a chain radical process characterized by a short active-center lifetime, bimolecular termination, and high rate of chain transfer to the complexed MMA. A kinetic scheme has been proposed for the propagation mechanism of alternating copolymerization in the presence of a complexing agent not requiring independent measurements of the equilibrium constant of complexation. It has been found that spontaneous and UV-initiated copolymerizations in the system have different mechanisms of initiation and a common mechanism of propagation. The propagation proceeds by addition of single monomers as well as donor-acceptor complexes of the comonomers to the propagation radicals, with the first mechanism being predominant. Inclusion of the monomers in the complex leads to an increase of the St reactivity and to a decrease of the MMA reactivity in propagation to the corresponding macroradicals in comparison with the reactivity of the free monomers. A number of kinetic and statistical parameters of the propagation reaction have been calculated.     

Radical terpolymerization of sulfur dioxide,styrene, and methyl methacrylate

The radical terpolymerization of sulfur dioxide, styrene, and methyl methacrylate in o-dichlorobenzene with 2,2′-azobisisobutyronitrile was carried out in order to clarify the propagation mechanism of the radical copolymerization of sulfur dioxide and styrene, especially as a function of total concentration of sulfur dioxide and styrene. From the analysis of the trigonal composition diagrams it has been definitely shown that the radical copolymerization of sulfur dioxide and styrene proceeds by the propagation of two monomers, but the usual type of copolymerization mechanism, explicable in terms of the Lewis-Mayo equation, is not applicable to this copolymerization. The participation in the propagation of a monomer charge-transfer complex consisting of sulfur dioxide and styrene was also ruled out.     

Grafting onto Wool. XXVII. Graft Copolymerization of MixeD Vinyl Monomers by Use of Ceric Ammonium Nitrate as Redox Initiator

In order to ascertain the effect of a donor monomer, vinyl acetate (VAc), on the graft copolymerization of acceptor monomers, ethyl acrylate (EA) and butyl acrylate (BA), grafting of mixed vinyl monomers (EA + VAc) and (BA + VAc) was carried out on Himachali wool in aqueous medium using ceric ammonium nitrate (CAN) as a redox initiator. Graft copolymerization was carried out at different temperatures for various reaction periods. Percent grafting and percent efficiency were determined as functions of 1) concentration of mixed vinyl monomers, 2) concentration of CAN, 3) concentration of HNO₃ 4) temperature, and 5) reaction time. VAc, the donor monomer, was found to decrease percent grafting of EA and BA onto wool.     

Polymerization of coordinated monomers VII. A kinetic study on the alternating copolymerization of methyl methacrylate with styrene using stannic chloride

The alternating copolymerization of methyl methacrylate with styrene in the presence of stannic chloride at ?50°C in toluene was kinetically investigated both under photoirradiation and with the tri-n-butylboron-benzoyl peroxide initiator. The concentrations of the binary and ternary molecular complexes in the copolymerization solution were estimated by use of the equilibrium constants. The rates are found to be proportional to the 1.5th and 1.0th orders of the concentration of the ternary molecular complex composed of stannic chloride, methyl methacrylate, and styrene, under photoirradiation and with initiator, respectively. The conversion increases proportionally with the polymerization time, while the degree of polymerization is constant irrespective of the time. The rates depend linearly upon the square root of the intensity of the incident light and upon the concentration of tri-n-butylboron, respectively. The alternating copolymerization is confirmed experimentally to precede the homopolymerization of the monomer charged in large excess both under photoirradiation and with initiator. The kinetic results indicate consistently that the alternating copolymerization proceeds through the homopolymerization of the ternary molecular complex in the steady state with a bimolecular termination. Both the conventional radical mechanism and the double complex mechanism are unsuitable for the present alternating copolymerization.     

Radiation-induced copolymerization of chlorotrifluoroethylene with ethyl vinyl ether

The radiation-induced copolymerization of chlorotrifluoroethylene with ethyl vinyl ether was investigated in the liquid phase at 20 and ?78°C over a wide range of monomer compositions. A copolymer was obtained in which the monomers alternate with regularity along the polymer chain over the entire range of monomer compositions investigated. Both the rate of copolymerization and the intrinsic viscosity of the resulting copolymer were found to depend strongly on the initial monomer composition, both reaching a maximum value at an equimolar concentration of the monomers. The monomer reactivity ratios were determined and correspond well with calculated values. A decrease in the irradiation temperature was accompanied by a marked decrease in the rate of copolymerization and the intrinsic viscosity of the copolymer.     

Electroinitiated polymerization of vinylic monomers in polar systems. III. Polymerization of acrylates and methacrylates in alcohol solutions

Methyl, ethyl, and n-butyl acrylates and methacrylates are polymerized by electroinitiation in methanol–, ethanol–, and n-propanol–electrolyte mixtures in which the monomers are soluble whereas the polymers obtained are insoluble. The technique of changing the polarity of the electrodes described earlier was used. The relationships between molecular weights and polymer yields as function of current density, initial monomer concentration and dielectric constant of the solvent are described. A kinetic scheme for the initiation, propagation, and termination is given.     

Alternating copolymerization of benzofuran and acrylic monomers in the presence of organoaluminum compounds

The copolymerization of benzofuran and acrylic monomers, such as acrylonitrile, methacrylonitrile, methyl acrylate, and methyl methacrylate, was investigated in the presence of aluminum compounds as complexing agents for acrylic monomers. Among the various kinds of aluminum compound, ethylaluminum sesquichloride is the most suitable for alternating copolymerization, whereas ethoxyaluminum compounds of low acidity allow the incorporation of excess acrylic monomer and dichloride of strong acidity is likely to induce cationic homopolymerization of benzofuran as a side reaction. The equimolar amount of sesquichloride with respect to acrylic monomer is necessary for alternating copolymerization. Azobisisobutylonitrile (AIBN) is an effective initiator but benzoyl peroxide is not. Nuclear magnetic resonance (NMR) of the copolymer indicates that the copolymer is essentially alternating, although some block sequences of acrylic monomer sometimes exist. As a mechanism the copolymerization via a ternary complex of acrylic monomer, aluminum compound, and benzofuran is considered. Free acrylic monomer participates in copolymerization when the amount or acidity of the complexing agent is insufficient. A quantitative relation between monomer and copolymer composition is derived from a scheme based on the copolymerization of the donor monomer-acceptor monomer complex with free acrylic monomer.     

“Reviews in Macromolecular Chemistry”

Abstract

In the homopolymerization and copolymerization of vinyl acetate with dibutyl maleate in the presence of the sodium salt of sulfosuccinic acid semiester with nonylphenol ethoxylated with 25 mol ethylene oxide, the initiator, potassium persulfate (KPS), has a higher decomposition rate than in water even after consumption of monomer. The value of the initiator productivity, P, defined as the ratio of the formed polymer over the decomposed KPS, decreases as the batch stage of the semicontinuous process proceeds. The initiator reacts either with free surfactant molecules or with those grafted on poly(vinyl acetate) chains. During the stage of continuous addition of monomers and KPS, a smaller initiator concentration no longer provides proportionality between the added and decomposed amounts of initiator. The increased monomer concentration at the beginning of continuous addition causes the rate of KPS splitting to decrease as most of the surfactant is bound to the surface monomer/polymer particles.     

Copolymerization of 2,3-Dihydropyran and Ethyl Vinyl Ether with Maleic Anhydride

2,3-Dihydropyran (DHP) and ethyl vinyl ether (EVE) were co-polymerized with maleic anhydride (MA) with benzoyl peroxide at 60°C, and 1:1 alternating copolymers were obtained. The rates were maximum at 1:1 monomer composition. Spontaneous copolymerization and solvent effect on the rate were observed in the copolymerization of DHP with MA, in which initial rates were slower in more polar solvents. Participation of charge transfer complex was considered. EVE copolymerized rapidly with MA, reaching the theoretical limiting conversion of 1:1 alternating copolymerization. Although DHP-MA comonomer pair and EVE-MA comonomer pair formed similar 1:1 charge transfer complexes, DHP copolymerized slowly with MA to produce a low molecular weight copolymer, and the limiting conversion was much lower than the theoretical one. To explain these, degradative chain transfer to DHP monomer is proposed as the initial rate of DHP-MA copolymerization is proportional to the initiator concentration to the power 1.1. Q and e values of DHP were calculated to be 0.013 and -0.93, respectively, from the monomer reactivity ratios of copolymerization of DHP with acrylonitrile [r₁ (DHP)=0.003 ± 0.006 and r₂ (AN)=3.6 ± 0.3].     

Some aspects of anionic butadiene copolymerization

The relationship between ideal copolymerization behavior and the nature of reactive species in butyllithium (n-BuLi) initiated anionic copolymerization of styrene (St)- butadiene (Bd) in nonpolar solvent has been discussed. The monomer reactivity ratios (m.r.r.) for various reactive species were evaluated by kinetic study and statistical approach (using ¹³C NMR data) in St-Bd anionic copolymerization system with THF as polar additive. The Markovian mechanisms for different propagating reactions in this complex copolymerizing system have been postulated. Furthermore, “pseudo” zero order Markovian mechnism could be sophisticatedly established in the n-BuLi/tertiary amyloxy potassium (t-AmOK)/THF initiated St-Bd copolymerization system, provided that the apparent rate constants of both monomers are equal. Thus, by adjusting the ratio of K/Li and THF/Li, copolymers with composition almost identical to the ratio of initial monomer feed composition at different stages of conversion could be obtained.     

Radical copolymerization of sulfur dioxide and chloroprene

The radical copolymerization of sulfur dioxide and chloroprene (CP) in benzene was carried out, especially as a function of the total monomer concentration ([SO₂] + [CP]). The composition of chloroprene polysulfones varies mainly with total monomer concentration and with polymerization temperature, but depends very slightly on feed composition. The microstructure of chloroprene units in chloroprene polysulfone was such that the trans-1,4 unit was predominantly over the cis-1,4 unit. Thus it would seem possible to rule out both radical copolymerization mechanisms, i.e., propagation of separate monomers as explained by the Lewis-Mayo equation, and propagation processes involving a monomer charge-transfer complex.     

Kinetics of Free Radical Copolymerization. IV. Rate of Initiation in the Copolymerization System Ethyl Acrylate-Styrene-Benzene

Dependence of the rate constant of initiation on the overall concentration and composition of monomer has been investigated in the free radical copolymerization of ethyl acrylate and styrene in bulk and in benzene solution at 50° C. The rate constant of initiation has been determined by the inhibition method using triphenyl-verdazil as the stable free-radical inhibitor. An equation has been derived to calculate the rate constant of initiation in a copolymerization system, where both monomers undergo a pseudounimolecular side reaction with the inhibitor. The rate constant of initiation in the copolymerization mixture is a linear composition of rate constants determined separately in the pure constituents of the system.     

基于Maple软件辅助绘制自由基二元共聚曲线的研究

运用数据处理软件(maple)对经典的自由基二元聚合公式进行图形绘制,得到了二元单体之间共聚关系的三组图.一是二元单体的自由基共聚曲线图F1-f1,二是聚合物中单体平均组成(Fp)与投料单体浓度(f1)的关系曲线图,三是聚合物转化率(C)与投料单体(f1)的关系曲线图.通过二组具有代表性的共聚实例,分别是有恒比点的非理...     

Copolymerization of vinyl acetate initiated by manganese tris(acetylacetonate)

Vinyl acetate forms a complex with manganese tris(acetylacetonate). A scientific hypothesis, according to which the use of manganese tris(acetylacetonate) as an initiator would lead to the increase in the relative activity of vinyl acetate in copolymerization with more active monomers, is suggested. To verify the hypothesis experimentally, an integrated study of the kinetics of binary copolymerization of vinyl acetate with N-vinyl (N-vinylsuccinimide and N-vinyl-3(5)methylpyrazole) and acrylic (2-hydroxyethyl methacrylate) monomers in various media is carried out. It is demonstrated on the basis of an analysis of copolymerization constants of the monomers under study that the relative activities of monomers in fact become closer. This leads to a change of the microstructure of polymers and results in macrochains with improved alteration of monomer units.