Free radical polymerization of unconjugated dienes: 18. Cyclopolymerization of o-divinylbenzene at 70°C

The free radical polymerization at 70°C of o-divinylbenzene in toluene solutions takes place according to a cyclopolymerization mechanism. By fitting the experimental data with two different relationships between the mole fraction of residual unsaturation in the polymers and the monomer concentration at which they were obtained, it has been possible to show that, in the chain propagation steps, intramolecular cyclization could occur involving the two monomeric units entered last in the polymer chain, with formation of seven-membered ring structures.     

Free radical polymerization of p-methyl styrene

An experimental investigation is reported of the free-radical synthesis kinetics of poly(p-methyl styrene) in cyclohexane at low monomer conversion in the temperature range 50°–70°C using AIBN initiator. The p-methyl styrene monomer contained greater than 97% paraisomer. Isothermal conversion/time curves were obtained using glass ampoule reactors and gravimetry and molecular weight distribution and weight-average molecular weights were measured by s.e.c. and low angle laser light scattering photometry (LALLSP). Transfer to small molecules (monomer, cyclohexane, —) was found to be small or negligible with virtually all of the polymer chains formed by termination by combination. Predicted and measured weight-average molecular weights are in good agreement for polymer synthesized at low conversions.     

Free radical polymerization of nitropropyl acrylates and methacrylates. I. Heat of polymerization

The heat of polymerization ΔH_p, of nitropropyl(meth)acrylate monomers has been studied by differential scanning calorimetry (DSC) in dynamic and isothermal modes. DSC showed that ΔH_p of 2‐nitropropyl(meth)acrylate was surprisingly smaller than that of propyl(meth)acrylate but similar to that of 2,2‐dinitropropyl(meth)acrylate. According to molecular structure analysis by a PM3 Hamiltonian in a MOPAC program, the contributing main factor to the lowering of ΔH_p of 2‐nitropropyl (meth)acrylate was found to be the hydrogen bond between the O(?C) and the H atom attached at position C6. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2929–2935, 2001     

Free radical polymerization with long chain branching: continuous polymerization of vinyl acetate in t-butanol

Vinyl acetate was polymerized in a continuous stirred tank reactor (CSTR) at 60°C in t-butanol solution. Mean residence times ranged from 1.35 to 7.2 hr; steady state conversions ranged from 15 to 61%. Molecular weights $\text{M}$_n and $\text{M}$_w were measured and interpreted in terms of a kinetic model developed from batch studies and the state of local mixing in the reactor. Good macroscopic mixing was confirmed by tracer studies and measurements of conversion vs time during the start-up period and at steady state. The molecular weights obtained at high conversions agreed more closely with predictions based upon a locally segregated state than with those based on complete molecular mixing. However, calculations based on agitation and diffusion rates raised serious questions about the validity of the segregation model for this polymerization. Other factors, some chemical and some related to the agitation, may be important, but the problem of predicting molecular structure remains unresolved.     

Free radical polymerization engineering—I: A new method for modeling free radical homogeneous polymerization reactions

This paper deals with a new appraisal of free radical polymerization modeling. Classical properties of the distribution of polymerization degrees and methods for studying them thanks to the z-transform are recalled. When simple mechanisms are involved, the kinetics may be represented by a “detailed analytic” model relying on macromolecule balances. This is no longer possible when complex processes are occurring, e.g. transfer to polymer, β-scission, terminal double bond propagation… In order to deal with these more complex cases, a “tendency model” is proposed, relying on balances of quantities such as free radicals, macromolecules and the moments of the distribution of polymerization degrees. The quality of the polymer is described by chemical characters such as double bonds, long and short branching points, terminal double bonds… for which kinetic equations are established. Equations are given for calculating the moments of free radicals and those of instantaneously produced macromolecules via various processes. The simplicity and the usefulness of the method are illustrated by several examples and a comparison is made, when possible, with the detailed approach. Finally, equations are given, making it possible to calculate the quality of polymer produced in any kind of reactor and for different states of segregation.     

Free radical polymerization of methyl methacrylate at high temperatures

Free-radical polymerization of methyl methacrylate in a tubular reactor has been conducted at above-Tg temperatures. A salient feature of these experiments is the very efficient control of reactor temperature by vapor-liquid equilibrium of the polymerizing mixture via monomer evaporation. The system pressure thus provides a powerful control variable, restricting the temperature in the entire reactor by changing the monomer evaporation rate. In the range of our experimental conditions, the temperature and pressure in the reactor follow the Antoine equation closely. High temperature runs also reduce the length requirement of the reactor. However, molecular weight averages of the products are not impressive, unless slow-burning initiators are used. Modeling of above-Tg reactions has been attempted at two-levels of sophistication. A plug-flow model gives predictions in good agreement with our experimental temperatures and conversion data. The predicted molecular weights are also consistent with the experimentally observed values. However, the more elaborate rheokinctic model suggests that the superficial agreement between model and experiment is due to initiator burn-out, which limits the final conversion to within 40 percent. The liquid layer next to the reactor wall can never be so viscous as to form a stagnant deposit, due to this conversion limitation. The velocity profiles are thus not very much distorted, and a plug-flow model is adequate. With a slow-burning initiator and a sufficiently long reactor, skewing of velocity profile and reactor channeling will eventually emerge. Hence, the rheokinetic model must be evoked to model the system under such conditions.     

Free radical polymerization of vinyl acetate in the presence of liquid polysulfides

The free radical polymerization of vinyl acetate in the presence of a liquid polysulfide H(SCH₂CH₂OCH₂OCH₂CH₂S)_nH (thiocol) was investigated from the point of view of reaction mechanism and characterization of the resulting copolymers. It was shown that, besides the thiol end groups that were consumed very rapidly, the disulfide groups within the thiocol chain were also involved in chain transfer processes. The chain transfer constant of the thiocol S–S groups in the polymerization reaction was estimated from their rate of consumption versus the rate of monomer consumption (C_T = 0.89). The resulting copolymers, made up of randomly distributed thiocol sequences and PVAc blocks, were characterized by ¹H NMR, GPC, DSC and TGA measurements. The copolymers displayed only one glass transition each, which decreased as the PVAc block length decreased, while their thermal stability was lower than that of both thiocol and PVAc. The molecular weight of the copolymers increased with VAc conversion as a consequence of the insertion of PVAc blocks within the thiocol chain.     

Polymerization kinetics for the preparation of poly(p-divinylbenzene) via a miniemulsion polymerization process

The polymerization kinetics for the preparation of poly(p-divinylbenzene (p-DVB)) via a miniemulsion polymerization process was studied by the gravimetric analysis and the transmission electron microscopy (TEM) analysis. The influence of the variation of both initiator concentration and polymerization temperature on the polymerization rate was investigated and also the activation energy of p-divinylbenzene was estimated. The evolution of polymer particles was observed by the electronmicrographs and the relatively large size of polymer particles without the formation of coagulum was obtained in the miniemulsion polymerization process.     

Studies on tributyl tin methacrylate II. Temperature dependence of the polymerization of tributyl tin methacrylate

In continuation of the earlier communication, we report here a detailed kinetic analysis of the polymerization of tributyl tin methacrylate initiated by azobisisobutyronitrile at the temperature range of 50–80°C. The initiator exponents are found to vary with temperature and viscosity of the medium reaching a low value of 0.40 at 50°C. This has been explained as due to primary radical termination which is very important in this system particularly at low temperatures. Energy of activation of viscous flow for this monomer is found to be approximately 4.2 kcal/mol which is substantially higher than for methyl methacrylate. The energy of activation for propagation has been determined applying the procedure of Fischer and Schulz and is 4.6 kcal/mol which is quite comparable to that of methyl methacrylate. The faster rate of polymerization of this monomer compared to other methacrylates has been attributed to lower rate of termination because of steric hindrance and viscosity effects. The energy of activation for initiation in this monomer seems to be quite high and comparable to values obtained for other vinyl monomers.     

Free radical polymerization of butyl acrylate in monodispersed droplets: Comparison between two heating strategies

Monodispersed droplets could be easily generated in coaxial microdevice, and a reaction based upon these discrete droplets is an attractive approach thanks to isolated reaction units, efficient mixing, and precise residence time control. In this work, free radical polymerization of butyl acrylate was conducted in monodispersed droplets of several hundred microns. Two different heating methodologies, microwave heating and conventional heating with oil bath were adopted to initiate polymerization, respectively. The polymerization under conventional heating could be regarded as an isothermal process, while the polymerization under microwave heating gradually underwent a temperature increase. So the poly (butyl acrylate) obtained by microwave heating has larger average molecular weight and higher polydispersity index. Meanwhile, the conversion of butyl acrylate was significantly improved by microwave heating compared with conventional heating, even though the reaction temperature under microwave heating might be lower than the temperature of the oil bath. This remarkable enhancement was a direct proof of the nonthermal effect of the microwave field for free radical polymerization. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Free radical polymerization in ionic liquids—Influence of the IL-concentration and temperature

The influence of the ionic liquid (IL) 1-ethyl-3-methylimidazoliumethylsulfate ([EMIM]EtSO₄) on the polymerization kinetics of methyl methacrylate was investigated. ILs are liquids with relatively high polarities and viscosities. These two characteristic properties are strongly correlated with the rate coefficients of propagation k_p and termination k_t of polymerizations carried out in ILs. The rate constant of termination k_t decreases when the concentration of ionic liquid, and thus the viscosity is increased, whereas the propagation rate coefficient k_p increases with increasing IL content. The viscosity of ILs can be varied by either working with mixtures of ILs with conventional organic solvents – here the IL [EMIM]EtSO₄ was mixed with dimethyl formamide (DMF) – or by variation of the temperature. The studies were carried out to determine the influence of the viscosity on the propagation and the termination reaction as well as the molecular weight distribution.     

Structural control in radical polymerization with 1,1 diphenylethylene: 2. Behavior of MMA-DPE copolymer in radical polymerization

Copolymers of 1,1-diphenylethylene (DPE) behave in a very special way in radical polymerization. Particularly, the behavior of MMA-DPE copolymers in radical polymerization is investigated. The results reveal that the semiquinoid structure of the precursor polymer identified in a previous contribution is activated by the attack of free radicals and thus, in a second stage polymerization with a second monomer, block copolymers are formed. The block copolymer yield depends strongly on the ratio between the amount of DPE-containing precursor polymer and the initiator and monomer concentration used in the second stage. The mechanism proposed is able to explain at least qualitatively all experimental results including the restriction of this mode of control of radical polymerization to the formation of diblock copolymers only.     

One photon-two radical-electron transfer photoinitiators. 2-(o-, m-, or p-Methoxypyridine)-p-pyrrolidinestyrilium methyl sulfates as photoinitiators of free radical polymerization

In this paper, the novel hemicyanine dye-borate pair, e.g. 2-((o, m, or p)-methoxypyridine)-p-pyrrolidinestyrilium methyl sulfates (MeOSp)-tetramethylammonium n-butyltriphenyl borate (TBAB) were evaluated and employed as the photoinitiating pairs of multiacrylate monomer polymerization. The kinetic studies clearly demonstrate that the modification of the dye structure by the exchange of the N-alkyl group on N-alkoxy one in pyridinium moiety causes a marked increase in the efficiency of photoinitiation of 2-ethyl-2-(hydroxymethyl)-1,3-propanediol triacrylate (TMPTA) polymerization.     

Free radical polymerization engineering—II: Modeling of homogeneous polymerization of styrene in a batch reactor,influence of initiator

A “tendency” model of free radical polymerization is used to re-investigate batch polymerization of styrene in solution in cyclohexane with slow and fast decomposing initiators. It is impossible to account for experimental data when a conventional mechanism involving only transfer to the monomer is assumed. In order to sucessfully represent mononer consumption and average molecular weights by number and by weight as a function of time for both initiators, two additional processes are required, i.e. transfer to and induced decomposition of the initiator (if transfer sites are available). The coresponding set of rate constants was determined. When a fast initiator is used, this polymerization is sensitive to mixing effects and could be utilized as a test reaction in polymer reactors. The elucidation of the role of the initiator is a good example of the usefulness of the “tendency” model for studying complex polymerization mechanisms.     

Free radical polymerization and lipid binding of lysozyme reacted with peroxidizing linoleic acid

Insolubilization and polymerization of proteins exposed to peroxidizing lipids may be due either to cross-linking with incorporation of fragments of the lipid oxidation products, or to free radical transfer from lipid to protein and subsequent free radical polymerization of protein. The second mechanism which has been proposed was inferred from measurements of electron spin resonance signals in proteins. In this study, uniformly labeled linoleic acid, [¹⁴C(U)] LA, was reacted with lysozyme. Volatile oxidation products of LA were also used in some experiments. Incubation was done in the absence of water. Oligomers of lysozyme, as well as the monomer, were isolated after incubation, and the [¹⁴C] label incorporated into each fraction was determined. The results show that the dominant mechanism of protein polymerization after exposure to peroxidizing linoleic acid is the transfer of free radical from lipid to protein, and subsequent free radical polymerization.     

Kinetics of radical polymerization,LIII. The absolute rate constants in the radical polymerization of ethyl acrylate

The dependence of dilution on the chain propagation and termination rate constants was investigated in the polymerization of ethyl acrylate in benzene solution at 50°C, with the rotating sector method. The errors of the above rate constants were determined and, by our method applied to decrease these errors, the errors of the propagation rate constant was reduced to its half value. By the application of our earlier results in polymerization kinetics, we found that in this system the chain propagation step is exclusively responsible for the solvent effects observed. Our experimental results can be quantitatively described in terms of the hot redical theory.     

Free radical polymerization of methyl methacrylate: Modeling and simulation under semibatch and nonisothermal reactor conditions

For the bulk free radical polymerization of methyl methacrylate (MMA), equations of the material balance can be written that are based on a kinetic diagram that considers initiation by decomposition of an AIBN initiator, propagation, and termination by disproportionation. To quantify the gel and glass effects simple empirical dependences are used between the rate constants of termination and propagation and monomer conversion. Numerical values for the empirical parameters at different temperatures and initiator concentrations are also given. Conversion history and molecular weights are obtained by simulation when an initiator or monomer are added to the reaction mass and the temperature modifies after some reaction has taken place. These intermediate operations are simulated at different moments with respect to the gel and glass effects. The validation of the model for semibatch and nonisothermal conditions are made by comparing the simulation results with literature experimental data. The most important conclusion of the article is that the empirical model proposed for the gel and glass effects can be successfully used under semibatch and nonisothermal reactor conditions. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2561–2570, 1999     

伴有水解缩合反应的种子乳液聚合动力学(I)模型

伴有水解缩合反应的自由基种子乳液聚合反应是制备有机-无机杂化乳胶粒的一种新方法，水解缩合反应和自由基聚合这两种反应在乳液体系中的动力学耦合过程决定了聚合产物的微结构和应用性质。通过单体的分配系数建立了单体在乳液体系中各相的分配模型，进而建立了考虑单体分配的自由基种子乳液共聚合的动力学模型。针对功能基团在乳液各相中水解缩合反应的特点，结合自由基种子乳液共聚合的动力学模型，建立了伴有水解缩合反应的自由基种子乳液聚合动力学模型。该模型反映了反应过程中的物质传递规律、非均相反应特点、自由基共聚合和水解缩合反应间的耦合关系。