Highly active peroxides in the radical polymerization of ethylene under high pressure — conversion and initiator usage

By using highly active peroxides, it is possible to reduce the polymerization temperature necessary for the synthesis of low density polyethylene. In order to examine a number of peroxides for their suitability as low temperature initiators, polymerization tests were carried out at 1900 bar, 70–140°C, with an average residence time of 30 s in a continuously operating laboratory facility equipped with a stirred autoclave. Apart from a number of perneodecanoates, two peroxy dicarbonates, a sulphonyl peroxide, and a difunctional peroxide were used. The initiator consumption was high at polymerization temperatures below 100°C. The results obtained with the different peroxides varied considerably. As the temperature increased, the initiator consumption decreased rapidly to reach almost the same level for all the individual peroxides at above 120°C. The difunctional compound that proved highly suitable for the low polymerization temperatures desired was 1,4-di-(2-neodecanoyl peroxy isopropyl)benzene, the consumption at 100°C of which amounted to 13 g initiator/kg PE. Using a quantity of 40 g initiator/kg PE, a reactor temperature of 82°C could be employed. The peroxy dicarbonates and tertiary butyl perneodecanoate gave less satisfactory results.     

Application of di-functional organic peroxides in the polymerization of ethylene under high pressures

The suitability of difunctional organic peroxides for the synthesis of low density polyethylene (LDPE) was examined with a view to improve the results. Polymerization tests were carried out in a stirrer autoclave pilot plant using three different difunctional compounds with different levels of thermal stability at a pressure of 1700 bar and temperatures of between 180 and 290°C. The conversion and the specific peroxide consumption were measured and the average molar masses of the polymers obtained were determined. The solubility of the peroxides in isododecane was also examined.     

Highly active MgO-supported TiCl4 catalyst for the ethylene polymerization

Summary The MgO-supported TiCl₄ catalysts prepared by heating MgO with TiCl₄ showed a high activity for the ethylene polymerization in combination with Et₃Al or i-Bu₃Al. In these highly active catalysts, it has been shown that MgCl₂ is formed in the MgO-TiCl₄ reaction and is considered to contribute to the enhancement of the activity of the catalysts.     

Radical high pressure polymerization of ethylene with stable initiators

In order to assess the suitability of stable initiators for the high pressure polymerization of ethylene, polymerization tests were carried out in a stirred autoclave in continuous operation. The pressure used was 1700 bar, the average residence time 30 seconds and the temperature was adjusted to between 200 and 360°C. The initiator concentration in the ethylene feed varied between 4 and 40 mol ppm. Di-tert-butyl peroxide, di-tert-amyl peroxide, tert-butyl hydroperoxide, and 3,4-di-methyl-3,4-di-phenyl hexane, a C? C labile compound, were chosen for use as stable initiators. The level of conversion and the specific initiator consumption were determined. The polymers obtained were characterized by measuring their density, average molecular weight, and melt flow index. The stable initiators used were all characterized by a very low level of consumption. In the case of dialkyl peroxides and alkyl hydroperoxide, the optimum application temperature is substantially above 200°C and above 300°C in the case of the C? C labile initiator. Under these conditions, polymers with a low density, a low molecular weight, a narrow molecular weight distribution and a high melt flow index were obtained.     

Radical terpolymerization of ethylene,methyl acrylate and vinyl acetate under high pressure. Physical properties of the polymers

Polymerization tests were carried out in a stirred autoclave designed for continuous operation in order to determine the influence of the reaction pressure and temperature and of the acrylic acid methyl ester and vinyl acetate comonomers on the ethylene-acrylic acid methyl ester-vinyl acetate terpolymer formed. Pressures between 1100 and 1900 bar and temperatures of 180 and 230°C were used. The average residence time was 40 seconds. Tertiary butyl perpivalate and tertiary butyl perethyl hexanoate in concentrations of 50 to 180 mol-ppm in the ethylene feed were used as initiators. The characteristic properties of the polymers obtained were assessed by determining their composition, density, crystallinity, melting point, glass transition temperature, melt index, the average molecular weight, tensile strength and elongation at break.     

Bulk polymerization of polyurethane under high pressure

The pressure effect on the reaction kinetics, molecular weight, and the microphase separation of the soft and hard segment of the polyurethane, synthesized under high pressure, was studied. The polymerization rate increased with increasing synthesis pressure and the activation energy of polymerization decreased with increasing synthesis pressure from 22.4 kcal/mol at 1 kg/cm² to 19.4 kcal/mol at 3000 kg/cm². The volume of activation of the polyurethane polymerization was ?19.8 cm³/mol at 60°C. Microphase separation between soft and hard segment decreased with increasing synthesis pressure and increased with increasing synthesis temperature. Molecular weight and molecular weight distribution were not influenced by the synthesis pressure.     

Synthesis of functional polymers under conditions of controlled atom-transfer radical polymerization

The major achievements in the field of controlled atom-transfer radical polymerization, the most promising method of living radical polymerization, are analyzed. The relationship between the structure of a regulating agent and its activity under the conditions of controlled radical polymerization, including the efficiency of metal-complex catalysts for the targeted synthesis of macromolecules with predetermined molecular-mass characteristics, chain structure, and properties, is examined. Main trends in the development of this area of polymer chemistry are highlighted.     

Heat transfer coefficient in a high pressure tubular reactor for ethylene polymerization

Heat transfer in tubular reactors for the high pressure polymerization of ethylene is very complex, since these tubular reactors are usually divided into several zones that exhibit different flow patterns and critical fouling behavior. The correct estimation of the overall heat transfer coefficient along the reactor axial distance is a major issue when assessing the predictive capabilities of a mathematical model for the process. In general, previous models employed either constant heat transfer coefficients or the usual correlations for the Nusselt number. Neither of these two approaches is accurate enough to allow a correct prediction of the reactor behavior with respect to temperature profiles and product molecular properties. The present work performs a more comprehensive estimation of the heat transfer coefficient in these reactors. At a first stage the overall heat transfer coefficients were estimated by using approapriate energy balances and a good set of experimental data. Then, a predictive model was proposed for the overall heat transfer coefficient. All flow regimes, as well as fouling effects, were taken into account, and the parameter estimation was based on temperature profiles obtained from an industrial reactor. The temperature profiles, conversions, pressures and molecular properties calculated by means of the experimentally fitted heat transfer coefficients or with the predictive model showed good agreement with plant data.     

Activation of the high pressure polymerisation of ethylene initiated with organic peroxides by means of organoaluminium compounds

In the course of this study, an activator system consisting of an aluminium trialkyl compound and a Lewis base was tested for its suitability for the radical polymerisation of ethylene at high pressure. The aim of reducing the initiator consumption and the polymerisation temperature was achieved with aluminium trialkyl alone without the use of a Lewis base. Among the aluminium trialkyl compounds examined, triethyl aluminium proved to be the most effective. This effectiveness is due to the increased rate of decomposition of the peroxide as a result of which a larger amount of free radicals becomes available thus increasing the rate of polymerisation. By using an addition of 50 mole ppm triethyl aluminium to 50 mole ppm tert-butyl-perpivalate in the ethylene feed it was possible to almost double the monomer conversion at a given polymerisation temperature and to reduce by half the consumption of peroxide initiator per kg polyethylene produced. Compared with the non-activated polymerisation, the polymerisation temperature was reduced from 150°C to 125°C, the initiator consumption remaining the same. The costs of the triethyl aluminium activator are more than offset by the increased yield and the decrease in initiator consumption.     

The preparation of new polymers by the high pressure polymerization of trivinyl benzene

1,3,5-Trivinyl benzene has been thermally polymerized at temperatures of 150°–340°C and pressures of 0.37–1.0 GNm^?2. The results show that the extent of conversion of the vinyl groups present, the density and modulus of rigidity of the polymer all increase with the temperature and pressure of polymerization. The highest moduli are more than three times those of polystyrene.Specific heats also fall as the density is increased. None of the crosslinked materials show a change in specific heat of the type associated with a glass transition at temperatures up to 500K.     

活性正离子聚合向活性自由基聚合转化法合成嵌段共聚物

通过枯基氯／四氯化钛／吡啶／异戊二烯活性正离子聚合反应体系制备了末端是叔氯基的聚异丁烯,经过脱氯化氢反应其分子链末端转化成异丁烯基．在9-硼二环[3,3．1]壬烷、氧气存在下引发苯乙烯的活性自由基聚合,成功地合成了异丁烯-苯乙烯嵌段共聚物,并用核磁共振仪对所得产物进行了表征。     

Highly active catalysts for ethylene polymerization by the reduction of TiCl4 with organomagnesium compounds

The effect of introducing metal halides other than AlCl₃ into a TiCl₃ catalyst, by the reduction of TiCl₄ with various metal alkyls is examined. Magnesium halides are shown to be most effective in increasing catalyst activity for the polymerization of ethylene. The influence of the type of organomagnesium compound on catalyst activity is studied, together with the effect of reaction conditions in the reduction step. The composition and structure of the catalysts is discussed. The results show conclusively that the activity of a TiCl₃ catalyst in the Ziegler polymerization of ethylene is strongly affected by the presence of other metal compounds.     

Preparation of highly active Cr-catalysts for ethylene polymerization

A Cr(CH₃COO)₃ · (CH₃CO)₂O/MgCl₂/AlEt₂Cl/2-EHA catalyst was prepared by modifying the Battelle catalyst with MgCl₂ in 2-ethyl-1-hexanol(2-EHA), and the polymerization of ethylene was carried out in toluene at 20–60°C. The rate of polymerization increased to reach an individual stationary value during the course of polymerization, and the stationary rate markedly increased with an increase in the molar ratio of Mg/Cr. The polyethylene obtained without MgCl₂ had a rather low molecular weight with a very broad polydispersity, whereas those obtained in the presence of MgCl₂ had extremely high molecular weights with narrow polydispersities.Polymerization of ethylene was subsequently performed under similar conditions using various types of metal chlorides in place of MgCl₂. A clear relation was found between the polymerization activity and the electronegativity X(M^x+) of metal ion in Mclx:metal chlorides having the electronegativities below X(Cr²⁺) accelerated the activity, whereas those above X(Cr²⁺) retarded it. A plausible mechanism for the enhancement of the activity by metal chlorides was proposed on the basis of these results.     

E.s.r. study of radical polymerization of pentaerythrityl monoacetal dimethacrylate in polystyrene matrix at high pressure

The e.s.r. spectrum of free radicals formed during polymerization of a bifunctional monomer of pentaerythrityl monoacetal dimethacrylate by thermal decomposition of benzoyl peroxide in a polystyrene matrix at 700 MPa is studied. Formation of propagating radicals of cyclopolymerization and crosslinking polymerization is discussed.     

Preparation of hyperbranched polymers by atom transfer radical polymerization

A cheap acrylic AB* monomer, 2‐(2‐chloroacetyloxy)‐isopropyl acrylate (CAIPA), was prepared from 2‐hydroxyisopropyl acrylate with chloroacetyl chloride in the presence of triethylamine. The self‐condensing vinyl polymerization by atom transfer radical polymerization (ATRP), a “living”/controlled radical polymerization, has yielded hyperbranched polymers. All the polymerization products were characterized by proton nuclear magnetic resonance spectroscopy (¹H NMR). CAIPA exhibited distinctive polymerization behavior that is similar to a classical step‐growth polymerization in the relationship of molecular weight to polymerization time, especially during the initial stage of the polymerization. However, a significant amount of monomer remained present throughout the polymerization, which is consistent with typical chain polymerization. Also, if a much longer polymerization time was used, the polymer became gel. As a result of the unequal reactivity of group A* and B*, the polymerization is different from an ideal self‐condensing vinyl polymerization: the branch structures of polymers prepared depend dramatically on the ratio of 2,2'‐bipyridyl to CAIPA. Hyperbranched polymers exhibit improved solubility in organic solvent, however, they have lower thermal stability than their linear analogs. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2114–2123, 2002     

Kinetics of the reaction between terephthalic acid and ethylene oxide under high pressure

Kinetics of the reaction between terephthalic acid and ethylene oxide in n-butanol solvent, catalyzed by triethyl amine, was investigated under high pressure. Effect of temperature, catalyst concentration, ethylene oxide to terephthalic acid ratio and stirrer speed was studied on the rate of formation of bis(2-hydroxy-ethyl)terephthalate. It was found that the reaction of terephthalic acid with ethylene oxide occurred in the liquid phase. The experimental data were correlated with a model based on S_N2 reaction mechanism and the activation energy of the reaction was found to be between 19.3–21.6 kcal/mole in the temperature range of 60–100°C.     

原子转移自由基聚合制备超支化聚合物进展

介绍了原子转移自由基聚合(ATRP)制备超支化聚合物的原理以及近年来采用ATRP方法制备的各种支化/超支化聚合物,展望了ATRP的发展趋势.ATRP是目前可控,活性聚合最成功的方法之一,它以过渡金属配合物为催化剂,通过有机卤化物引发乙烯基单体的自由基聚合,合成相对分子质量可控、相对分子质量分布窄的多种聚合物.     

A rheological effect in the reaction of dissolved polymers with peroxides under shearing stress

Reactions of polyisoprene, polybutadiene and polyoctenamer in o-xylene with dibenzoyl peroxide and dicumyl peroxide were investigated by measuring the apparent viscosity η_a of the solutions with a coaxial cylinder viscometer. As a new effect a ‘pre-maximum’ in the increase of η_a with reaction time was found. Possible reasons for the pre-maximum being due to the measuring device could be excluded. The dependence of the pre-maximum on the reaction conditions was investigated. A probable explanation of the pre-maximum is that the network first formed is destroyed by shear.