The high pressure polymerization of pure ethylene

A series of pure ethylene polymerizations performed to maximum pressures of 2,5 kbar and temperatures up to 250°C is discussed. The rate data which are obtained via quantitative infrared and near infrared spectroscopy closely fit to an overall polymerization rate law of the order 2,5 ± 0,2 in the ethylene concentration. The overall activation energy is determined to be 136,3 ± 6 kJ/mol. For the initiation reaction an activation energy of 209,8 ± 12 kJ/mol is derived. This fairly large value establishes that in dense high purity ethylene a thermally initiated (spontaneous) reaction to high molecular weight material occurs.     

Reaction mechanism of oxygen-initiated ethylene polymerization at high pressure

The kinetics of the oxygen-initiated polymerization of ethylene at high pressure up to 2,220 kbar was systematically investigated in a constant volume system in a temperature range from 60 to 250°C. In the higher temperature range (above 190°C), where no induction period exists, rate equations for both the oxygen consumption and the polymerization were derived by considering a retardation reaction by oxygen. The numerical calculation of these equations by the Runge-Kutta-Gil method indicated an excellent agreement with experimental results.     

Photo-sensitized polymerization of styrene under high pressure

The polymerization of styrene, photosensitized by azocyclohexane-1,1′-dinitrile, was studied at 30°C over a pressure range of 1 to ca. 1000 bar. The average lifetimes of the growing polymer chains were determined by the rotating-sector method. By measuring the effect of pressure on the individual reactions of styrene polymerization, the activation volumes for the propagation and the termination were obtained as ?17,9 cm³/mol and 13,1 cm³/mol, respectively. The overall activation volume was also measured as ?17,9 cm³/mol and was nearly equal to that calculated from the individual activation volumes (?17,8 cm³/mol). The propagation rate constant increases exponentially with pressure, whereas the termination rate constant decreases rapidly up to 500 bar and then decreases slowly as the pressure increases further.     

Photosensitized polymerization of butyl acrylate under high pressure

The propagation and termination rate constants for butyl acrylate polymerization under high pressure at 30°C were measured by the rotating sector method. The effect of pressure on the individual rate constant was determined and the activation volumes for the propagation and the termination were obtained as ?22,5 cm³/mol and 20,8 cm³/mol, respectively, and the overall activation volume was ?26,3 cm³/mol. The rate constant and its dependence on pressure were compared with data previously obtained on methyl methacrylate and butyl methacrylate polymerizations, and the problem concerning the differences of the pressure effect between these reactions were discussed.     

Photosensitized polymerization of butyl methacrylate under high pressure

The propagation and termination rate constants for butyl methacrylate polymerization were measured at 30°C over a pressure range of 1 to 1 000 bar at a 250 bar pressure interval. By determining the effect of pressure on the individual reactions of polymerization, the activation volumes for the propagation and the termination were obtained as ?23,2 cm³/mol and 17,8 cm³/mol, respectively. The overall activation volume was ?17,4 cm³/mol. The effect of pressure on the individual rate constants for butyl methacrylate polymerization was compared with the results for methyl methacrylate polymerization. The comparison shows that, for the propagation reaction, the increase in the size of the ester group brings about a diminution in the value of the activation volume, and that the effect of pressure on the termination reaction was somewhat smaller than that for methyl methacrylate polymerization.     

Photosensitized polymerization of vinyl acetate under high pressure

By use of the rotating sector technique under high pressure, the changes which occur in the rate constants of the propagation and the termination reactions in the polymerization of vinyl acetate, photosensitized with azocyclohexane-1,1′-dicarbonitrile were studied at 30°C over a pressure range of 1 to 1000 bar. The effects of pressure on the individual rate constants were determined and the activation volumes of propagation and termination were obtained as ?24,0 and 16,3 cm³ mol^?1, respectively. The effect of pressure on the propagation reaction of vinyl acetate was somewhat larger than those of styrene and methyl methacrylate, and the termination rate constant showed a smaller decrease with pressure than those of the other vinyl monomers, especially of methyl methacrylate. The problem concerning the differences of the pressure effect on the termination reaction is discussed from the view point of the chain transfer reaction to monomer.     

Photosensitized polymerization of octyl methacrylate under high pressure

By use of the rotating sector technique under high pressure, the changes of the rate constants of propagation and termination in the polymerization of octyl methacrylate, Photosensitized with 1,1′-azocyclohexane-1,1′-dicarbonitrile, were studied at 30°C over a pressure range of 1 to 1000 bar at 250 bar pressure intervals. The effects of pressure on the individual rate constants were determined and the activation volumes of propagation and termination were obtained as ?24,7 and 20,8 cm³ mol^?1, respectively. The overall activation volume was ?19,2 cm³ mol^?1. The effects were compared with the results for methyl and butyl methacrylate polymerizations. The increase in the size of the ester groups brought about a diminution in the value of the activation volume for the propagation reaction. The effect of pressure on the termination mechanism was discussed from the view point of the viscosity effect on the diffusion-controlled termination.     

Photosensitized polymerization of methyl methacrylate under high pressure

By use of rotating sector technique at high pressure, the average life times of the growing polymer radical in the bulk polymerization of methyl methacrylate was measured over the pressure range of 1—1000 kg/cm² at 250 kg/cm² pressure interval. The rates of initiation at the same pressure interval was also determined by the measurement of consumption of the inhibitor using N′,N′-diphenyl-N-picrylhydrazyl as radical scavenger. The effect of pressure on the individual rate constants for the methyl methacrylate polymerization was evaluated from both experimental results and the activation volumes of the propagation and the termination was obtained as ?19,0 and 25,0 cm³/mol, respectively. Their values have been compared with those of styrene polymerization.     

Super fast polymerization under high pressure and plastic flow

Simultaneous action of high pressure and shear deformation on various organic compounds is studied using an apparatus of Bridgeman anvil type. This apparatus allows to work in a temperature range from ?196°C to 200°C at different shear forces. It is established that under these conditions the investigated materials are in the plastic flow state. Chemical transformations of more than 300 organic compounds of different chemical classes are observed. Reactions such as polymerization, polycondensation, polyaddition etc. are realized under plastic flow. In addition, copolymerization reactions with the formation of random copolymers occur for some substances. Kinetic peculiarities of the polymerization process under plastic flow are investigated on the example of acrylamide.     

Excimer laser-induced free-radical copolymerization of ethylene and acrylonitrile

The free-radical copolymerization of ethylene (E) and acrylonitrile (A) was studied up to 275°C and 2900 bar in continuously and in discontinuously operated devices. Polymerization is induced by KrF excimer laser light at 248 nm. In addition, results for copolymerizations with thermal and with chemical (oxygen) initiation are presented. The ethylene reactivity ratio, r_E, is derived as a function of temperature. At 2450 bar, r_E increases from 0,016 ± 0,003 at 150°C up to 0,055 ± 0,009 at 275°C. r_E measured as a function of pressure, yields an activation volume of ΔV^# (r_E) = (?5,2 ± 3,5) cm³·mol^?1. The kinetic information from the laser-induced experiments is used to describe the measured overall quantum yield, ?₀, which is found to be a few thousand monomer molecules polymerized by one absorbed laser photon. ?₀ decreases toward higher acrylonitrile content. The kinetic parameters are also used to predict overall and acrylonitrile conversion in continuous free-radical E/A copolymerizations with various chemical initiators.     

Irreversible activation effects in ethylene polymerization

Activation and deactivation phenomena commonly observed in the case of slurry or gas phase ethylene polymerization kinetics are associated to molecular aspects of the formation and inhibition of active centers. As a preliminary study of the problem, we have to identify what step during the formation or action of the active centers is concerned by the well-known activating agents: temperature, ethylene pressure and α-olefins addition. They all lead to an irreversible increase in the polymerization rate, which can be attributed to the creation of new active centers. Hydrogen was also considered, since it is an activator for propene polymerization, but it deactivates ethylene polymerization. This deactivation is often partially reversible. Different explanations of this complex behaviour are presented.     

Free-radical polymerization kinetics of methyl methacrylate at very high conversions

The free-radical polymerization of methyl methacrylate (MMA) at very high conversions (x > 0,8) was studied in the temperature range 60C° to 160C°. 2,2′-Azodiisobutyronitrile (AIBN) and benzoyl peroxide (BPO) were used as initiators. In the case of the latter, decomposition kinetics at very high monomer conversions was investigated, too. For temperatures T ? 120C° where depropagation can be neglected a simple kinetic model based on “reaction diffusion” and free volume theory was developed. The model contains only a single adjustable parameter, the critical free volume fraction V*. Good agreement between model predictions and experiments was obtained. V* is independent of initial initiator concentration and reaction temperature, and there is some evidence that V* is also independent of the chemical nature of the initiator.     

Homo- and copolymerization of ethylene at high temperature with cationic zirconocene catalysts

Homo- and copolymerization of ethylene with 1-hexene were conducted at different temperature and ethylene pressure with several zirconocenes activated with dimethylanilinium tetrakis(pentafluorophenyl)borate (Me₂PhNH·B(C₆F₅)₄)/triisobutylaluminium (i-Bu₃Al) to study the effect of ligand structure and polymerization conditions on catalytic activity, molecular weight and chain transfer reactions. At high temperature and low ethylene pressure, rac-ethylene(bisindenyl)zirconium dichloride (rac-Et(Ind)₂ZrCl₂) activated with Me₂PhNH·B(C₆F₅)₄/i-Bu₃Al initially gives a highly active catalyst that is rapidly deactivated. trans-Vinylene double bonds, which were not formed at low temperature, were detected in polyethylene synthesized at high temperature and low ethylene pressure. They reasonably arise from β-H transfer after isomerization reaction. The molecular weight of ethylene/1-hexene copolymers decreases with increasing 1-hexene feed, followed by the formation of vinylidene end groups. This reveals that β-H transfer from propagating chains containing primary inserted 1-hexene as a terminal unit is predominant. This reaction is influenced by the ligand structure. At high temperature and high ethylene pressure, trans-vinylene and vinylidene contents decrease and the vinyl content increases, indicating that the high ethylene pressure controls β-H transfer after isomerization reaction.     

Alterations in brain monoamine neurotransmitter release at high pressure

Summary High pressure exposure produces neurological changes which manifest as tremors, EEG changes and convulsions. Since previous studies have implicated the involvement of the monoaminergic system in these symptoms, it was of interest to study monoamine release at high pressure. Synaptosomes isolated from guinea pig brain were used to follow monoamine efflux at 68 ATA. The major observation was a decrease in the initial calcium dependent release of all three monoamines in response to K⁺ induced depolarization. This response is similar to that previously observed for GABA, glycine and glutamate. This generalized pressure induced depression of initial transmitter release suggests a mechanism common to the release process for both excitatory and inhibitory neurotransmission.     

Synthesis and polymerization of poly(ethylene glycol) fumarates

Fumaric esters of poly(ethylene glycol) ( 1a–d ) were prepared as macromonomers. The halfesters 1a and 1c were obtained by interaction of maleic anhydride with the monoethers of poly(ethylene glycol) ( 2a and 2b ) in the presence of 4-dimethylaminopyridine, and the diesters 1b and 1d by esterification of methyl hydrogen fumarate ( 13 ) with the monoethers of poly(ethylene glycol) ( 2a and 2b ). The macromonomers were found to homopolymerize and to copolymerize with styrene and methyl methacrylate following a radical polymerization mechanism.