Kinetic study of γ-radiation-induced polymerization of ethylene in the presence of acetylene

The effects of acetylene on the γ-radiation-induced polymerization of ethylene were studied from the viewpoint of kinetics. The experiments were carried out under a pressure of 150–400 kg/cm²; the temperature was 30°C; the dose rates were 2.7 × 10⁴ and 1.1 × 10⁵ rad/hr; the acetylene content was 0–2.21%. Both the polymer yield and the molecular weight increased acceleratively with the reaction pressure in the polymerization containing 0.18% acetylene. The yield increased almost proportionally with the dose rate, and the molecular weight was found to be almost independent of the dose rate in the polymerization containing 2.21% acetylene. The polymerization rate and the molecular weight increased with reaction time, but the increment decreased with increasing acetylene content. The degree of increase in the molecular weight also decreased with increasing time. These results were analyzed by using a graphical evaluation method for kinetics, and the effects of acetylene on each elementary step in the polymerization discussed.     

Effect of oxygen on the γ-radiation-induced polymerization of ethylene

The effects of oxygen on the γ-radiation-induced polymerization of ethylene were studied at a temperature of 30°C.; the pressure was 400 kg./cm.², the dose rate was 1.9 × 10⁵ rad/hr.; and oxygen content was from 1–2000 ppm. The main product was solid polymer, and no liquid product was found. The gaseous products were hydrogen, acetylene, higher hydrocarbons, carbon dioxide, aldehydes, and acids. Several kinds of carbonyls similar to those formed in γ-ray oxidized polyethylene were observed in the polymer. The polymer yield and the degree of polymerization decreased markedly with increasing oxygen content, while the amount of carbonyls in the polymer increased. The number of moles of polymer chain and the amounts of hydrogen and acetylene were found to be almost independent of the oxygen content. The polymerization of pure ethylene was not affected by carbon dioxide and formic acid. On addition of acetaldehyde, the polymer yield and the degree of polymerization decreased markedly, while the number of moles of polymer chain increased. In the polymerization of ethylene containing oxygen, both the rate of oxygen consumption and the carbonyl content of the polymer increased, while the inhibition period decreased by the addition of acetaldehyde. It was found that the degree of polymerization after the inhibition period is almost independent of the reaction time in the presence of acetaldehyde, while it increases with the time in the absence of acetaldehyde.     

Effect of acetylene on the γ-radiation-induced polymerization of ethylene

The effects of acetylene on the γ-radiation-induced polymerization of ethylene were studied from the viewpoint of the gaseous products and polymer structure. The experiments were carried out under a pressure of 400 kg/cm²; the temperature was 30°C; the does rate was 1.1 × 10⁵ rad/hr; and the acetylene content was 0–20%. The solid polymer was obtained in the polymerization of ethylene containing 2.2% acetylene, while the monomer containing 19.7% acetylene gave a yellowish viscous oil. The polymer yield and molecular weight decreased remarkably with acetylene content. The main gaseous product was hydrogen, and trace amounts of butane, butene-1, butadiene-1,3, and benzene and its derivatives were also observed. The rate of formation of hydrogen was almost independent of acetylene content and there was no difference in acetylene contents before and after the irradiation was found. The infrared spectra of the polymers showed the presence of vinylidene, trans-vinylene, and terminal vinyl unsaturations, 1,4-disubstituted benzene, and carbonyl groups. The contents of trans-vinylene, terminal vinyl, and methyl groups increased with acetylene content, and that of vinylidene was independent of acetylene content. The monomer reactivity ratios of ethylene and acetylene were evaluated as 45.5 and 66.0, respectively. On the basis of the results, the effects of acetylene on the γ-radiation-induced polymerization of ethylene were discussed.     

Kinetics of the gamma-radiation-induced polymerization of ethylene in tert-butyl alcohol

The gamma-radiation-induced polymerization of ethylene in the presence of 13–30 ml of tert-butyl alcohol was carried out under a pressure of 120–400 kg/cm² at a dose rate of 1 × 10³ to 2.5 × 10⁴ rad/hr at 30°C with a 100 ml reactor. The polymerization rate and the molecular weight of the polymer increased with reaction time and pressure and decreased with amount of tert-butyl alcohol. The polymer yield increased almost proportionally with the dose rate, while the molecular weight was almost independent of it. These results were graphically evaluated, and the rate constants of initiation, propagation, and termination for various conditions were determined. No transfer was observed. On the basis of these results the role of tert-butyl alcohol in the polymerization is discussed.     

Mechanism of initiation in the γ-radiation-induced polymerization of ethylene

The relation between the gaseous products and the reaction conditions such as pressure, temperature, and dose rate in the γ-radiation-induced polymerization of ethylene was studied. The main gaseous products were hydrogen and acetylene, and the amounts of these products increased linearly with reaction time, monomer density, and dose rate, while they were independent of reaction temperature. The ratio of rate of formation of hydrogen to acetylene was about one-half. Further, it was found that the number of moles of polymer chain formed was almost equal to that of acetylene at room temperature. An initiation mechanism in which both hydrogen and acetylene are formed is proposed. The equation which is derived on the basis of the initiation mechanism is shown to be in good accordance with the experimental results.     

Short-chain branching in γ-radiation-induced polymerization of ethylene

In an attempt to elucidate the mechanism of chain-branch formation in the polymerization of ethylene, the effect of reaction conditions on short-chain branching in γ-radiationinduced polymerization of ethylene was investigated by using infrared spectroscopy. The concentration of methyl groups, i.e., the frequency of short-chain branching, increases with temperature and pressure and is independent of ethylene conversion to polymer and radiation intensity. The number of methyl groups per polymer molecule increases almost proportionally with the degree of polymerization. These facts indicate that short-chain branching occurs mainly by the mechanism of intramolecular hydrogen transfer. The effect of pressure on the rate of chain branching can be postulated by considering the transition state to be six-membered rings in hydrogen transfer reactions. The activation energy of chain branching is found to exceed that of propagation by 6 kcal./mole.     

Kinetics of the γ-radiation-induced polymerization of ethylene in liquid carbon dioxide

The γ-radiation-induced polymerization of ethylene with the use of liquid carbon dioxide as a solvent, was studied from the viewpoint of kinetics. The polymerization was carried out at conversions less than 10% under the pressure ranging from 100 to 400 kg./cm.², dose rates 1.3 × 10⁴?1.6 × 10⁵ rad/hr., and temperatures of 20–90°C. The concentration of carbon dioxide varied up to 84.1 mole-%. The polymerization rate and the polymer molecular weight were observed to increase with reaction time. This observation, however, becomes less pronounced with increasing concentration of carbon dioxide and with rising temperature. The exponents of the pressure and the dose rate were determined to be 2.3 and 0.85 for the rate, and 2.0 and ?0.20 for the molecular weight, respectively. From the kinetic considerations for these results, the effect of carbon dioxide on the initiation and termination reaction in the polymerization was evaluated.     

γ-Ray-induced copolymerization of ethylene and vinyl chloride in liquid carbon dioxide

The γ-ray-induced copolymerization of ethylene and vinyl chloride with the use of liquid carbon dioxide as a solvent was studied under a total pressure of 400 kg/cm², with a dose rate of 2.5 × 10⁴ rad/hr at 30°C. A rubberlike, sticky polymer is obtained when the molar concentration of vinyl chloride is less than 30% in the monomer mixture, and the polymer is a white powder at higher concentrations of vinyl chloride. Infrared, x-ray, and differential thermal analyses confirm that the polymerization products are noncrystalline, true random copolymers. The rate of copolymerization decreases markedly when a small amount of vinyl chloride is added to ethylene monomer. In the range of vinyl chloride concentration higher than 5%, however, the rate and the molecular weight of copolymer increase with increasing concentration of vinyl chloride. It has been concluded from kinetic considerations based on these results that the rate of initiation increases proportionally with the concentration of vinyl chloride. Further, the growing chain radicals are shown to be deactivated by the cross-termination reaction between the radicals with terminal unit of ethylene and vinyl chloride, and no transfer reaction occurs.     

杂多酸引发四氢呋喃聚合反应 Ⅱ.水的反应行为

前报我们对低腐蚀性非均相的磷钨杂多酸Ｈ３ＰＷ１２Ｏ４０（ＰＷ１２）引发体系进行了研究［１］,发现环氧乙烷（ＥＯ）可有效地促进ＰＷ１２引发的四氢呋喃（ＴＨＦ）聚合反应,大幅度地降低了引发剂用量,聚合物收率显著提高,并发现聚合过程中不存在链终止反应．产物...     

Tailoring MWD of Bimodal Polyethylene in the Presence of Ziegler-Natta Catalyst

Summary: Linear poly (ethylene-co-1-butene) was produced through two-step polymerization in one reactor using a Ziegler-Natta catalyst, where in the first step, low molecular weight homopolymer of ethylene in the presence of hydrogen and in the next step, high molecular weight copolymer of ethylene with 1-butene in the absence of hydrogen were produced. Molecular weight distribution of bimodal polyethylene was tailored through adjustment of polymerization time of each stage and hydrogen concentration of the first stage. Increasing hydrogen concentration shifted the molecular weight distribution curve to the lower molecular weights and broadened molecular weight distribution while interestingly increased high molecular weight incorporation of copolymer produced in the second stage due to increasing of reaction rate in the second step. To achieve bimodal molecular weight distribution, the polymerization times of the first and the second steps, which are highly dependent on the amount of hydrogen, were adjusted properly. The effects of the mentioned parameters on the processability as well as rheological properties of some samples were investigated. The rheological results showed shear thinning behavior of all specimens and confirmed the changes in molecular weight and molecular weight distribution. It was also demonstrated that the melt miscibility between low molecular weight and high molecular weight fractions improved with increasing of chains having very low molecular weight.     

γ-Radiation-initiated post-polymerization of methacrylic acid in the solid state

The solid-state postpolymerization of slowly crystallized methacrylic acid was studied at 0°C with ⁶⁰Co γ-radiation as the initiator. The yield, molecular weight, molecular weight distribution, and stereosequencing of the polymer product were determined as a function of polymerization time. The narrow molecular weight distribution and the linear dependence of molecular weight on polymer yield were attributed to a polymerization mechanism characterized by both independent chain propagation and essentially no termination step. The overall polymerization rate was substantially faster than that reported previously for shock-crystallized monomer, a result which was attributed to termination by the occlusion of propagating radicals at defects in the shock-crystallized monomer. Although largely atactic, the polymer synthesized in the solid state contained a secondary kind of stereosequencing; the meso triad probability was highest at the end of the chain, where propagation had initiated and decreased continuously with chain growth. The gradient in stereosequencing along the chains was attributed to defects that were introduced into the monomer crystals by the growing polymer chains.     

Radiation-induced homogeneous polymerization of ethylene in cyclohexane

The radiation-induced polymerization of ethylene in cyclohexane was carried out in a reactor of 100 ml capacity under a range of temperature of 25–150°C, dose rate of 4.1 × 10⁴–2.9 × 10⁵ rad/hr, pressure of 200 kg/cm², and amount of cyclohexane of 20–90 ml. The polymerization was found to proceed at a steady state from the beginning. The polymerization rate is maximum at ca. 50 ml of cyclohexane. The dose rate exponent of the polymerization rate was 0.6 at every temperature from 25 to 150°C. The polymer molecular weight is in the range of 10³–10⁴, independent of dose rate, and decreases with increasing amount of cyclohexane. The molecular weight distribution is unimodal and narrow. Kinetic analysis of these results indicates that the polymerization proceeds via a simple scheme of homogeneous polymerization and the polymer molecular weight was determined by the chain transfer reaction which takes place mostly with cyclohexane. The unimodal and narrow molecular weight distribution is also consistent with the homogeneous polymerization scheme.     

Radiation-induced emulsion polymerization of ethylene. II. Effect of potassium myristate concentration and dose rate on the rate of polymerization in connection with polymer properties,kinetics, and mechanism

Radiation-induced emulsion polymerization of ethylene with potassium myristate as an emulsifier was studied in connection with the kinetics and the mechanism. The molecular weight of polymer was relatively low, of the order of 10³, when a sufficient amount of emulsifier was used. However, polyethylene gel was produced in the absence of a sufficient amount of emulsifier. The rate of polymerization was proportional to the 0.5 power of dose rate and increased slightly with increasing emulsifier concentration. The rate of seeded polymerization followed a similar trend to that for conventional polymerization. Kinetic analysis of these results suggests that the escape of radicals produced by chain transfer of propagating radical with the emulsifier and the monomer from polymer particles into the aqueous phase plays an important part in the rate of polymerization. The melting temperature and the crystallinity of the polymer significantly decreased with increasing polymerization temperature in the range 40–60°C.     

Effects of hydrogen in ethylene polymerization and oligomerization with magnesium chloride‐supported bis(imino)pyridyl iron catalysts

The effects of hydrogen in ethylene polymerization and oligomerization with different bis(imino)pyridyl iron(II) complexes immobilized on supports of type MgCl₂/AlEt_n(OEt)_3–n have been investigated. Hydrogen has a significant activating effect on polymerization catalysts containing relatively bulky bis(imino)pyridyl ligands, but this is not the case in ethylene oligomerization with a catalyst containing relatively little steric bulk in the ligand. It was found that the presence of hydrogen in the latter system led to decreased activity and an overall increase rather than a decrease in product molecular weight, indicating deactivation of active species producing low molecular weight polymer and oligomer. Decreased formation of vinyl‐terminated oligomers in the presence of hydrogen can therefore contribute to the activating effect of hydrogen in ethylene polymerization with immobilized iron catalysts, if it is assumed that hydrogen activation is related to chain transfer after a 2,1‐insertion of a vinyl‐terminated oligomer into the growing polymer chain. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4054–4061, 2007     

Two-stage irradiation study on propagation and termination in the γ-radiation-induced polymerization of ethylene in liquid carbon dioxide

The propagation and termination reaction in the γ-radiation-induced ethylene polymerization in liquid carbon dioxide were investigated by a two-stage irradiation. After irradiation at high dose rate, the polymerization occured at a considerable rate under the extremely low dose rate without initiation. The absolute propagation rate was determined in the second stage to be proportional to the square of ethylene fugacity and depended slightly on dose rate. The apparent activation energy for the propagation reaction is ?9 kcal./mole. From these observations which are the same as those in bulk polymerization, it is concluded that carbon dioxide acts as a diluent of ethylene monomer in the propagation reaction. Also, carbon dioxide was shown to be inactive to the growing radicals without irradiation, but oxygen which is produced by the radiolysis of carbon dioxide at high dose terminates the growing radicals with formation of carbonyl in the polymer.     

Kinetic features of ethylene polymerization over supported catalysts [2,6‐bis(imino)pyridyl iron dichloride/magnesium dichloride] with AlR3 as an activator

The effects of polymerization temperature, polymerization time, ethylene and hydrogen concentration, and effect of comonomers (hexene‐1, propylene) on the activity of supported catalyst of composition LFeCl₂/MgCl₂‐Al(i‐Bu)₃ (L = 2,6‐bis[1‐(2,6‐dimethylphenylimino)ethyl] pyridyl) and polymer characteristics (molecular weight (MW), molecular‐weight distribution (MWD), molecular structure) have been studied. Effective activation energy of ethylene polymerization over LFeCl₂/MgCl₂‐Al(i‐Bu)₃ has a value typical of supported Ziegler–Natta catalysts (11.9 kcal/mol). The polymerization reaction is of the first order with respect to monomer at the ethylene concentration >0.2 mol/L. Addition of small amounts of hydrogen (9–17%) significantly increases the activity; however, further increase in hydrogen concentration decreases the activity. The IRS and DSC analysis of PE indicates that catalyst LFeCl₂/MgCl₂‐Al(i‐Bu)₃ has a very low copolymerizing ability toward propylene and hexene‐1. MW and MWD of PE produced over these catalysts depend on the polymerization time, ethylene and hexene‐1 concentration. The activation effect of hydrogen and other kinetic features of ethylene polymerization over supported catalysts based on the Fe (II) complexes are discussed. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5057–5066, 2007     

Preparation of bimodal HDPEs with metallocene on Cr‐montmorillonite support

Previously described Cr‐montmorillonite (Cr‐MMT) was found to retain reactivity in the ethylene polymerization reaction regardless of which alkyl‐metal was used for workup in the preparation process, as long as alkylaluminium was used as a cocatalyst in the actual polymerization reaction. Introduction of hydrogen pressure was found to regulate the polymerization to give the product polymer with a narrower weight distribution, albeit with a somewhat smaller average molecular weight. Supporting metallocene onto Cr‐MMT produced a binuclear catalyst system which gave rise to bimodal polyethylene (PE). Polymer composition of the produced high density polyethylenes (HDPEs) could be controlled by changing factors such as the polymerization conditions and the identity of the metallocene compounds. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3722–3728, 2010     

Synthesis and characterization of poly(ethylene oxide‐co‐ethylene carbonate) macromonomers and their use in the preparation of crosslinked polymer electrolytes

Methacrylate‐functionalized poly(ethylene oxide‐co‐ethylene carbonate) macromonomers were prepared in two steps by the anionic ring‐opening polymerization of ethylene carbonate at 180 °C, with potassium methoxide as the initiator, followed by the reaction of the terminal hydroxyl groups of the polymers with methacryloyl chloride. The molecular weight of the polymer went through a maximum after approximately 45 min of polymerization, and the content of ethylene carbonate units in the polymer decreased with the reaction time. A polymer having a number‐average molecular weight of 2650 g mol^?1 and an ethylene carbonate content of 28 mol % was selected and used to prepare a macromonomer, which was subsequently polymerized by UV irradiation in the presence of different concentrations of lithium bis(trifluoromethanesulfonyl)imide salt. The resulting self‐supportive crosslinked polymer electrolyte membranes reached ionic conductivities of 6.3 × 10^?6 S cm^?1 at 20 °C. The coordination of the lithium ions by both the ether and carbonate oxygens in the polymer structure was indicated by Fourier transform infrared spectroscopy. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2195–2205, 2006     

Application of Monte Carlo simulation method to polymerization kinetics over Ziegler–Natta catalysts

In the current work, the Monte Carlo simulation method was applied to ethylene polymerization over Ziegler–Natta catalysts. As expected, polymerization over each center of a Ziegler–Natta catalyst leads to a polymer having a Schultz–Flory molecular weight distribution. Notwithstanding, the total molecular weight distribution obtained by all catalyst centers together is at least twice as broad as that of each center. As another interesting finding, the introduction of hydrogen to the reaction deactivates the catalyst active centers and thereby reduces the catalyst activity. Nevertheless, it does not mainly affect the polymerization kinetics. In addition, the polymer molecular weight falls as hydrogen is added to the reaction since it acts as a strong transfer agent. The same effect is seen when cocatalyst concentration increases. Hydrogen also widens the polymer molecular weight distribution. © 2008 Wiley Periodicals, Inc. Int J Chem Kinet 41: 45–56, 2009     

Effect of dose rate on emulsion and microemulsion polymerization of styrene

Emulsion and microemulsion polymerization of styrene were initiated with a gamma ray to study the effect of dose rate on polymerization. In both systems, there is an apparent plateau of polymerization rate in the curve of reaction rate vs. conversion. It was shown that emulsion polymerization conformed to the Smith–Ewart theory very well. Changing the dose rate in interval 2 had no great influence on polymerization rate, but it changed the average lifetime of radicals in polymer particles and affected the molecular weight of polymer produced. For microemulsion polymerization it was assumed that in the plateau it is the number of growing polymer particles being kept constant, not the number of polymer particles. When the dose rate was changed while the polymerization came into the constant period, the polymerization rate and the molecular weight of the polymer varied with the dose rate. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 257–262, 1998