Low-pressure Ethylene Polymerization Research Articles

Towards NHC stabilized alkylgallium alkoxide/aryloxide cations – The advances, the limitations and the challenges

Here we describe and discuss an approach to the synthesis of alkylgallium alkoxide and aryloxide cations stabilized with N-heterocyclic carbenes (NHCs). The reaction of methyl abstracting agent B(C6F5)3 with Me2Ga(OAr,CNHC) complexes stabilized by aryloxide ligands with N-heterocyclic carbene functionalities (1 and 2) has led to the formation of cationic complexes [MeGa(OAr,CNHC)]22+ (32+ and 42+). [3][MeB(C6F5)3]2 and [4][MeB(C6F5)3]2, which are the first examples of alkylgallium aryloxide cationic complexes, have been isolated and characterized by both spectroscopic and X-ray techniques. In contrast, the reaction of alkoxide derivative Me2Ga(O,CNHC) (5) with B(C6F5)3 and [Ph3C][B(C6F5)4] has led to the formation of adducts Me2Ga(O,CNHC)·B(C6F5)3 (6) and [Me2Ga(O,CNHC)·Ph3C]+. Although, the reactions of B(C6F5)3 with Me2Ga(OC6H4OMe)(SIMes) (7) or Me2GaOMe(SIMes) (8) (SIMes = 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene) have resulted in the formation of cationic species [MeGaOR(SIMes)]+, as evidenced by spectroscopic techniques, the side reactions resulting in the formation of (SIMes)B(C6F5)3 and boron alkoxide species have also been observed. Cationic complexes [3][MeB(C6F5)3]2 and [4][MeB(C6F5)3]2 are poor catalysts for the ring-opening polymerization of cyclic esters and are essentially not active in the low pressure polymerization of ethylene.

Nanocellulose Aerogels for Supporting Iron Catalysts and In Situ Formation of Polyethylene Nanocomposites

Aerogels of nanocellulose (NC) prepared by freeze‐drying of cellulose nanofibrils (CNF) hydrogels and followed by impregnation with methylaluminoxane serve as nanoporous organic supports for immobilizing single site iron catalysts such as bisiminopyridine iron(II) complexes. The resulting catalyst systems, exploiting renewable biomaterials as organic supports, are highly active in low pressure ethylene polymerization. They afford simultaneous control of high density polyethylene (HDPE) particle morphology and facile NC dispersion within the HDPE matrix. In the early stage of ethylene polymerization, mesoscopic shape replication and NC‐mediated templating yield platelets containing an NC core and a HDPE shell, as confirmed by scanning electron microscopy (SEM) of virgin polyethylene powders. Opposite to conventionally dried CNF hydrogels, forming large agglomerates, this facile NC aerogel‐mediated in situ NC/HDPE nanocomposite formation is vastly superior to melt compounding of HDPE with NC, failing to produce such fine NC dispersions. On increasing NC content to 3.0 wt%, both Young's modulus (+50%) and tensile strength (+40%) increase at the expense of elongation at break (−80%). According to the SEM analysis of NC/HDPE morphology, the dispersion of NC nanosheets together with the in situ formation of “shish‐kebab” polyethylene fiber‐like structures accounted for HDPE matrix reinforcement.

Silica powder obtained by sol-gel method as a support of organometallic vanadium catalyst for ethylene polymerization

Sol-gel technique was employed to obtain the silica-type powder, which after modification procedure was applied as a support of organometallic catalytic system for ethylene polymerization. The powder product was synthesized using hydrolysis and condensation of TEOS, catalyzed by ammonia. Obtained material and a reference support (commercial silica Davisil) were characterized to determine their particle size distributions, BET surface area, pore volume and diameter. Gas-phase adsorption of vanadium catalyst on analyzed support materials as well as adsorption from the solution in hexane were carried out. Both carrier materials were thermally pretreated prior catalytic systems syntheses and the influence of modification method applied on resulting organometallic catalyst character was estimated in low-pressure slurry polymerization of ethylene. Obtained results prove that sol-gel material, due to its advantageous morphology with wide and shallow pores, allows to obtain catalytic systems of higher activity in low-pressure ethylene polymerization, in comparison with commercial silica Davisil.

Catalytic Polymerization and Post Polymerization Catalysis Fifty Years After the Discovery of Ziegler's Catalysts

AbstractDuring the 1950's the discoveries of Ziegler's organometallic catalyst systems and Natta's stereoselective olefin polymerization set the stage for extraordinary progress in polymer science and technology. Today advanced catalyst systems are available for catalytic carbon carbon bond formation by means of polyinsertion, metathesis, coupling reactions, and controlled radical polymerization. Modern catalytic olefin polymerization processes and polyolefins are environmentally friendly and meet the demands of a sustainable development. The architectures of homo‐ and copolymers based upon olefin, cycloolefin, diene, styrene and arene feed stocks are tailored as a function of single site catalysts' ligand frameworks. Polymer properties are varied over a very wide range, e.g., liquid/solid, rigid/soft, crystalline/amorphous/rubbery, permeable/impermeable, opaque/transparent, moldable/thermosetting, insulating/conducting. Advanced polymerization reaction engineering, copolymerization processes, reactor granule and reactor blend technologies, tailor‐made single site catalysts, catalyst blends and tandem catalysis improve property profiles, stability, morphology, and melt processing. Tuned cycloolefin polymers are new functional materials for electronic applications. Catalytic chain transfer (CCT) and atom transfer polymerization (ATRP) produce a variety of new functional polymers, reactive oligomers, and block copolymers. Aqueous polyolefin emulsions are obtained when catalytic olefin polymerization is performed in nanodroplets of catalyst miniemulsions. The scope of catalytic polymerization and post polymerization catalysis is progressing well beyond the frontiers of commodity polyolefin manufacturing. Advanced catalytic processes produce polar polymers such as polyethers, polyketones, polyesters, polycarbonates, polyamides, polyaramids, and polyimides. The new phosgene free polycarbonate syntheses are based upon the palladium catalyzed oxidative carbonylation. This overview highlights history, recent progress and modern trends in catalytic polymerization and catalytic polymer modification illustrated by selected examples. Ziegler's glass reactor for performing his Mülheim low pressure ethylene polymerization. The reactor is on display at the Max Planck Institut für Kohlenforschung in Mülheim (this picture was made available by courtesy of G. Fink).magnified imageZiegler's glass reactor for performing his Mülheim low pressure ethylene polymerization. The reactor is on display at the Max Planck Institut für Kohlenforschung in Mülheim (this picture was made available by courtesy of G. Fink).

Crystal Structure, Morphology, and Phase Transitions in Syndiotactic Polypropylene

Abstract The discovery of a new catalyst for the low temperature and low pressure polymerization of ethylene by Ziegler at the Mulheim Institute in Germany in the mid-1950s opened the door to a whole new world in the synthesis of polyolefins [1]. Shortly thereafter, Natta and his group at the Milan Insti-tute in Italy announced that propylene and higher a-olefins could also be polymerized by the use of coordination catalysts, for example Tic], -Al(eth), F [2, 3]. The discovery of stereospecific polymerization allowed steric control on the growth of polymer chains for the first time. A major consequence of this polymerization is a significant effect of stereoregularity on physical, in particular, and mechanical properties. Another major con-tribution by Natta and his group was the development of methods for characterizing polymer configurations and conformations.

Chemistry of organochromium complexes on inorganic oxide supports. 4. Study of ethylene polymerization over chromocene on silica catalysts

The activity of chromocene on silica catalysts in low pressure polymerization of ethylene was studied under static conditions. The catalytic activity was dependent upon the ethylene pressure, the dehydration temperarure of the silica and the amount of the deposited Cr.

Porous structure of titanium-aluminium catalysts supported on alumina for low-pressure ethylene polymerization

Porous structure of titanium-aluminium catalysts supported on alumina for low-pressure ethylene polymerization

Studies of alumina as a support of titanium catalyst for low-pressure ethylene polymerization

Studies of alumina as a support of titanium catalyst for low-pressure ethylene polymerization

Low-pressure ethylene polymerization in the presence of catalysts obtained from phenoxyl-derivatives of titanium and sesquiethylchloroaluminium

Low-pressure ethylene polymerization in the presence of catalysts obtained from phenoxyl-derivatives of titanium and sesquiethylchloroaluminium

Dependence of the activity of titanium-aluminium complexes during polymerization of ethylene on the nature of the aryloxy radicals bound to the titanium atom

The authors have studied the catalytic activity of organic titanium-aluminium complexes obtained by the interaction of Ti(OAr) 2Cl or Ti(OAr) 4 with Al(C 2H 5) 2 where Ar = C 6H 4X (X=H, Me- p, Me- m, OMe- p, OMe- m, Cl- p, Cl- m and Br- p) on low pressure polymerization of ethylene. The activity of the complexes studied rised with increase in the acceptor properties of the aryloxy groups. A quantitative relation was found between change in the positive charge on the titanium atom and the rate of the elementary reactions of polymerization of ethylene. The relation between the growth rate of the polymer chain and the constants σ of the substituents in the aromatic cycle is described by the Hammett equation. The influence of the nature of the aryloxy radicals on the properties of PE is shown.

Polyisoprene

Abstract From the time, more than, a century ago, that isoprene was isolated by pyrolysis of natural rubber, scientists around the world have attempted to reverse the process, namely, to prepare rubber from isoprene. Bouchardat, in 1879, reported what may have been the first preparation of a synthetic rubbery material. It was done by treating isoprene with hydrochloric acid. This report signalled the start of a vigorous search for a system capable of converting isoprene into a useful rubber. The quest, though not fully successful, led to the discovery of efficient catalysts, such as the alkali metals, for use in anhydrous polymerizations and catalysts for aqueous emulsion polymerizations. Yet the preparation of an all cis-1,4-polyisoprene, a duplicate of natural rubber, continued to elude the most extensive efforts of scientists for many more years. It was not until the mid 1950's that two independent catalyst systems, each capable of polymerizing isoprene to a cis-1,4-polymer, were disclosed. One such catalyst came briefly on the heels of the famous discovery, by Nobel Laureate Karl Ziegler, of transition metal halide coordination catalysts for the low pressure polymerization of ethylene. Home and coworkers, employing a Ziegler-type catalyst prepared from trialkylaluminum and titanium tetra-chloride, polymerized isoprene to an essentially all cis-1,4-polyisoprene. The other catalyst, based on lithium metal, was discovered by a Firestone Tire and Rubber research team. The discovery was part of a broad study on structures and molecular weights of polyisoprenes prepared with alkali metals. The polymerization of isoprene in the presence of alkali metals was the subject of other extensive investigations. A polyisoprene with 90% 1,4 units was reportedly synthesized with the aid of lithium catalysts as early as 1949. Once the capability of converting isoprene to a high cis-1,4-polyisoprene was achieved, it was only required that isoprene be available at low cost for synthetic cis-1,4-polyisoprene to become a commercial reality. Thus, while the search for an economical isoprene source was underway, teams of scientists tackled an array of new problems related to stereoregular solution polymerization. The requirements for high purity, the optimization of the polymerization conditions, and the complex finishing processes, all put a great demand on the ingenuity and skill of research and development staffs. It was therefore rather remarkable that, in 1960, just a few years after the discovery of the stereospecific catalysts, the first commercial plant for the production of cis-polyisoprene with a lithium catalyst was on stream. By 1967 two other commercial polyisoprenes were being produced in the United States with catalysts based on trialkylaluminum-titanium tetrachloride. Additional production facilities went on stream in other countries. It was estimated that 670 000 long tons of cis-polyisoprene was produced in 1975. In more recent years oil shortages, inflation and related economic and political factors have curtailed U. S. production. A vast amount of literature has sprung up in the wake of this stunning commercial growth. Several comprehensive reviews have covered developments in this field. A symposium held in Moscow in 1972, exclusively dedicated to polyisoprene rubber, revealed the intensity and breadth of new work on synthetic polyisoprenes. The Eastern nations have been very active in polyisoprene research. A rough count of recent titles indicates that about two-thirds originate in the USSR and contiguous countries. We believe this review adequately covers the polyisoprene literature through 1977. It is not exhaustive because of the volume of publications and because many references appear in Chemical Abstracts as “Title only translated”.

Ethylene polymerization studies with supported cyclopentadienyl, arene, and allyl chromium catalysts

AbstractHighly active catalysts for low pressure ethylene polymerization are formed when chromocene, bis (benzene)‐ or bis (cumene)‐chromium or tris‐ or bis (allyl)‐chromium compounds are deposited on high surface area silica‐alumina or silica supports. Each catalyst type shows its own unique behavior in preparation, polymerization, activity, isomerization, and response to hydrogen as a chain transfer agent. The arene chromium compounds require an acidic support (silicaalumina) or thermal aging with silica to form a highly active catalyst. At 90°C polymerization temperature arene chromium catalysts produced high molecular weight polyethylene and showed, in contrast to supported chromocene catalysts, a much lower response to hydrogen as a chain transfer agent. An increase in polymerization temperature caused a significant decrease in polymer molecular weight. Addition of cyclopentadiene to supported bis (cumene)‐chromium catalyst led to a new catalyst which showed a chain transfer response to hydrogen typical of a supported chromocene catalyst. Polymerization activity with tris‐ or bis (allyl)‐chromium appears to depend on the divalent chromium content in the catalyst. Changes in the silica dehydration temperature of supported allyl chromium catalyst have a significant effect on the resulting polymer molecular weight. High molecular weight polymers were formed with catalysts that were prepared using silica dehydration temperatures below about 400°C. Dimers, trimers, and oligomers of ethylene were usually formed with catalysts that were prepared on silica dehydrated much above 400°C. The order of activity of the different types of catalysts was chromocene/silica > chromocene/silica‐alumina > bis (arene)‐chromium/silica‐alumina ≃ allyl chromium/silica.

Improved temperature control in low-pressure ethylene polymerization unit by using two control channels

Improved temperature control in low-pressure ethylene polymerization unit by using two control channels

Studies on the low pressure polymerization of ethylene by use of catalysts containing potassium alkyls

AbstractThe low pressure polymerization of ethylene by use of catalysts prepared from either butyl or amyl potassium, or the reaction product of potassium with chlorobenzene and titanium tetrachloride was studied. The efficiency of the catalysts depended on the molar ratio of the potassium alkyl to titanium tetrachloride but was in every case considerably lower than that of the corresponding lithium or sodium alkyl containing catalysts. Optimum molar ratios of the butyl potassium–titanium tetrachloride catalysts were between 2.8 to 6.1 with sharp drops on both sides of the optimum; for the amyl potassium between 1.1 to 3.7. The reaction product of potassium with chlorobenzene yielded much weaker catalysts with titanium tetrachloride, and the properties of the polymers obtained were different. The physical properties of the polyethylenes obtained, as determined from x‐ray diffraction diagrams, infrared spectra, and from melting points, showed similarity to those obtained with the lower alkali metal catalysts. The lower activity of the potassium catalysts may be related to the large ionic radius of the potassium, which influences the properties of the catalyst complex formed with titanium tetrachloride. Propylene did not undergo polymerization with the potassium alkyl containing catalysts at low pressure.

Studies on the low pressure polymerization of ethylene using catalysts containing sodium alkyls

AbstractThe low pressure polymerization of ethylene with the use of catalysts prepared from various sodium alkyls and titanium tetrachloride was studied. Catalysts prepared from amylsodium were very active over a wide range of molar ratios of amylsodium to titanium tetrachloride (2–50); the activity decreased sharply with lower molar ratios. Rate of polymerization was found to decrease sharply, probably as a result of fusing of polyethylene particles to the catalyst surface during polymerization. Up to a pressure of about three atmospheres, the polymerization gave better yields with increase in pressure, but no increase in rate was observed on using higher pressures. Yields increased also with lowering of temperature; 0°C. gave the best yields. Molecular weight determinations showed that the polyethylenes produced had high molecular weights which did not vary over a wide range. With butylsodium, catalysts similar to those with amylsodium were formed; they showed a smaller optimum range (5–9) of molar ratios of alkyl sodium to titanium tetrachloride. Catalysts prepared from phenylsodium were much weaker, and the optimum molar ratio of phenylsodium to titanium tetrachloride, contrary to the other sodium alkyls, was found to lie at much lower molar ratios of alkyl sodium to titanium tetrachloride. Polymerizations were, in the case of phenylsodium, accompanied by an induction effect. Preliminary studies on the preparation of catalysts for the low pressure polymerization of ethylene in the presence of cyclopentadienylsodium and titanium tetrachloride were as yet not successful.

Studies on the low pressure polymerization of ethylene using catalysts containing lithium alkyls

AbstractThe low and atmospheric pressure polymerizations of ethylene using catalysts prepared from n‐butyl lithium or isoamyl lithium and titanium tetrachloride were studied. The efficiency of the catalyst depended on the molecular ratio of the alkyl lithium to titanium tetrachloride. Optimum molecular ratio for the n‐butyl lithium–titanium tetrachloride was found to be between 2.15–2.47 with a sharp drop between 2.15–1.49; for the isoamyl lithium the optimum was between 2.5–4.3. Within the examined interval (of atmospheric pressure to a pressure of 60–70 lb./sq. in.) higher pressure caused an increase in the yield of polyethylene. No pronounced effect in polymerization was found in the temperature interval of −10–55°. The catalyst is stable for a few days if kept refrigerated. Petroleum ether, b.p. 40–80°, was the best solvent both for the preparation of the catalyst and for the polymerization. Ligroin, toluene, and especially ether interfered with the polymerization. The polyethylenes obtained melted between 125–135°.

The nature of some soluble catalysts for low pressure ethylene polymerization

Publisher Summary This chapter discusses the nature of some soluble catalysts for low-pressure ethylene polymerization. Soluble catalysts for the low-pressure ethylene polymerization have been found which are less active than the best heterogeneous catalysts, but which are much more suitable for the basic research on chemical nature of the catalysts. The soluble catalytic system obtained from organo-aluminium compounds and Ti compounds in which the Ti atom is bound to two cyclopentadienyl groups. A crystallizable bimetallic complex has been synthesized which is a catalyst for the polymerization of ethylene. It can be concluded that the Ziegler-type polymerization catalysts are complexes containing organometallic bonds and more than one metal atom.