1 Polyolefins Walter Kaminsky University of Hamburg, Hamburg, Germany I. INTRODUCTION The polyolefins production has increased rapidly in the 40 years to make polyolefins the major tonnage plastics material worldwide. In 2003, 55 million tons of polyethene and 38 million t/a polypropene were produced [1]. These products are used for packing material, receptacles, pipes, domestic articles, foils, and fibers. Polyolefins consist of carbon and hydrogen atoms only and the monomers are easily available. Considering environmental aspects, clean disposal can be achieved by burning or by pyrolysis, for instance. Burning involves conversion to CO 2 and H 2 O, exclusively. By copolymerization of ethene and propene with higher n-olefins, cyclic olefins, or polar monomers, product properties can be varied considerably, thus extending the field of possible applications. For this reason terpolymers of the ethene/propene n-olefin type are the polymers with the greatest potential. Ethene can be polymerized radically or by means of organometallic catalysts. In the case of polyisobutylene a cationic polymerization mechanism takes place. All other olefins (propene, 1-butene, 4-methylpentene) are poly- merized wi th organometalli c catalysts. The existen ce of several types of polyethene as well as blends of these polymers provides the designer with an unusual versatility in resin specifications. Thus polyethene technology has progressed from its dependence on one low-density polymer to numerous linear polymers, copolymers, and blends that will extend the use of polyethene to many previously unacceptable applications. Polypropene also shows versatility and unusual growth potential. The main advantage is improved susceptibility to degradation by outdoor exposure. The increase in the mass of polypropene used for the production of fibers and filaments is inive of the versatility of this polymer. Synthetic polyolefins were first synthetisized by decomposition of diazomethane [2]. With the exception of polyisobutylene, these polymers were essentially laboratory curiosities. They could not be produced economically. The situation changed with the discovery of the high pressure process by Fawcett and Gibson (ICI) in 1930: ethene was polymerized by radical compounds [3]. To achieve a sufficient polymerization rate, a pressure of more than 100 MPa is necessary. First produced in 1931, the low density polyethene (LDPE) was used as isolation material in cables. Due to its low melting point of less than 100  C LDPE could not be applied to the production of domestic articles that would be used in contact with hot water. Copyright 2005 by Marcel Dekker. All Rights Reserved. Important progress for a broader application was made when Hogan and Banks [4] (Phillips Petroleum) and Ziegler et al. [5] found that ethene can be polymerized by means of activated transition metal catal yst systems. In this case the high density polyethene (HDPE), a product consisting of highly linear polymer chains, softens above 100  C. Hogan polymerized ethene using a nickel oxide catalyst and later a chromium salt on an alumina-silica support. Zletz [6] used molybdenum oxide on alumina in 1951 (Standard Oil); Fischer [7] used aluminum chloride along with titanium tetrafluoride (BASF 1953) for the production of high-density polyethene. The latter catalyst has poor activity and was never used commercially. Zieglers [5] use of transition metal halogenides and aluminum organic compounds and the work of Natta [8] in applying this catalyst system for the synthesis of stereoregular polyolefins were probably the two most important achievements in the area of catalysis and polymer chemistry in the last 50 years. They led to the development of a new branch of the chemical industry and to a large production volume of such crystalline polyolefins as HDPE, isotactic polypropene, ethane-propene rubbers, and isotactic poly(l-butene). For their works, Ziegler and Natta were awarded the Nobel Prize in 1963. The initial research of Ziegler and Natta was followed by an explosion of scientific papers and pa tents covering most aspects of olefin polymerization, catalyst synthesis, and polymerization kinetics as well as the structural, chemical, physical, and technological characteristics of stereoregular poly- olefins and olefin copolymers. Since that first publication, more than 20 000 papers and patents have been published on subjects related to that field. Several books and reviews giving detailed information on the subjects of these papers have been published [9–19]. The first generation of Ziegler–Natta catalysts, based on TiCl 3 /AlEt 2 Cl, was characterized by low polymerization activity. Thus a large amount of catalyst was needed, which contaminate d the raw polymer. A washing step that increased production costs was necessary. A second generation of Ziegler–Natta catalysts followed, in which the transition metal compound is attached to a support (MgCl 2 , SiO 2 ,Al 2 O 3 ). These supported catalysts are of high activity. The product contains only traces of residues, which may remain in the polymer. Most Ziegler–Natta catalysts are heterogeneous. More recent developments show that homogeneous catalyst systems based on metallocene-alumoxane and other single-site catalysts can also be applied to olefin polymerization [20–23]. These systems are easy to handle by laboratory standards, and show highest activities and an extended range of polymer products. The mechanism of Ziegler–Natta catalysis is not known in detail. A two-step mechanism is commonly accepted: First, the monomer is adsorbed (p-complex bonded) at the transition metal. During this step the monomer may be activated by the configuration established in the active complex. Second, the activated monomer is inserted into the metal–carbon bond. In this sequence the metal-organic polymerization resembles what nature accomplishes with enzymes. Ziegler–Natta catalysts are highly sensitive, to oxygen, moisture, and a large number of chemical compounds. Therefore, very stringent requirements of reagent purity and utmost care in all manipulations of catalysts and polymerization reactions themselves are mandatory for achieving experimental reproducibility an d reliability. Special care must be taken to ensure that solvents and monomers are extremely pure. Alkanes and aromatic compounds have no substantial effect on the polymerization and can therefore be used as solvents. Secondary alkenes usually have a negative effect on polymerization rates, and alkynes, allenes (1,2-butadiene), and conjugated dienes are known to act as catalyst poisons, as they tend to form stable complexes. Copyright 2005 by Marcel Dekker. All Rights Reserved. Almost all polar substances exert a strong negative influence on the polymerization. COS and hydrogen sulfide, particularly, are considered to be strong catalyst poisons, of which traces of more than 0.2 vol ppm affect a catalyst’s activity. Neither the solvent nor the gaseous monomer should contain water, carbon dioxide, alcohols, or other polar substances in excess of 5 ppm. Purification may be carried out by means of molecular sieves. The termination of the polymerization reaction by the addition of carbon monoxide is used to determine the active centers (sites) of the catalyst. Hydrogen is known to slightly reduce the catalyst’s activity. Yet it is commonly used as an important regulator to lower the molecular weights of the polyethene or polypropene produced. II. POLYETHENE The polymerization of ethene can be released by radical initiators at high pressures as well as by organometallic coordination catalysts. The polymerization can be carried out either in solution or in bulk. For pressures above 100 MPa, ethene itself acts as a solvent. Both low- and high-molecular-weight polymers up to 10 6 g/mol can be synthesized by either organometallic coordination or high pressure radica l polymerization. The structure of the polyethene differs with the two methods. Radical initiators give more-or-less branched polymer chains, whereas organometallic coordination catalysts synthesize linear molecules. A. Radical Polymerization Since the polymerization of ethene develops excess heat, radical polymerization on a laboratory scale is best carried out in a discontinuous, stirred batch reactor. On a technical scale, however, column reactors are widely used. The necessary pressure is generally kept around 180 to 350 MPa and the temperature ranges from 180 to 350  C [24–29]. Solvent polymerization can be performed at substantial lower pressures and at tem- peratures below 100  C. The high-pressure polymerization of ethene proceeds via a radical chain mechanism. In this case chain propagation is regulated by dispropor tionation or recombination. ð1Þ ð2Þ ð3Þ Copyright 2005 by Marcel Dekker. All Rights Reserved. The rate constants for chain propagation and chain termination at 130  and 180 MPa can be specified as follows [30]: M p ¼ 5:93  103 L  mol À1 s À1 M t ¼ 2  108 L  mol À1 s À1 Intermolecular and intramolecular chain trans fer take place simultaneously. This determines the structure of the polyethene. Intermolecular chain transfer results in long flexible side chains but is not as frequent as intramolecular chain transfer, from which short side chains mainly of the butyl type arise [31,32]. Intermolecular chain transfer: ð4Þ ð5Þ Intramolecular chain transfer: ð6Þ ð7Þ Radically creat ed polyethene typically contains a total number of 10 to 50 branches per 1000 C atoms. Of these, 10% are ethyl, 50% are butyl, and 40% are longer side chains. With the simp lified formulars (6) and (7), not all branches observed could be explained [33,34]. A high-pressure stainless steal autoclave (0.1 to 0.51 MPa) equipped with an inlet and outlet valve, temperature conductor, stirrer, and bursting disk is used for the synthesis. Best performance is obtained with an electrically heated autoclave [35–41]. To prevent self-degeneration, the temperature should not exceed 350  C. Ethene and intitiator are introduced by a piston or membrane compressor. An in-built sapphire window makes it possible to observe the phase relation. After the polymerization is finished, the reaction mixture is released in two steps. Temperature increases are due to a negative Joule–Thompson effect. At 26 MPa, ethene separates from the 250  C hot polymer melt. After further decompression down to normal pressure, the residu al ethene is removed [42–46]. Reaction pressure and temperature are of great importance for the molecular weight average, molecular weight distribution, and structure of the polymer. Generally, one can say that with increasing reaction pressure the weight average increases, the distribution becomes narrower, and short- and long-chain branching both decrease [47]. Copyright 2005 by Marcel Dekker. All Rights Reserved. Oxygen or peroxides are used as the initiators. Initiation is very similar to that in many other free-radical polymerizations at different temperatures according to their half-live times (Table 1). The pressure dependence is low. Ethene polymerization can also be started by ion radiation [48–51]. The desired molecular weight is best adjusted by the use of chain transfer reagents. In this case hydrocarbons, alcohols, aldehydes, ketones, and esters are suitable [52,53]. Table 2 shows polymerization conditions for the high-pressure process and density, molecular weight, and weight distribution of the polyethene (LDPE). Bunn [54] was the first to study the structure of polyethene by x-ray. At a time when there was still considerable debate about the character of macromolecules, the demonstration that wholly synthetic and crystalline polyethene has a simple close-packed structure in which the bond angles and bond lengths are identical to those found in small molecules such Table 1 Peroxides as initiators for the high-pressure polymerization of ethene. Peroxide Molecular weight Half-time period of 1 min by a polymerization temperature (  C) (H 3 C) 3 -COOC(CH 3 ) 3 146.2 190 174.2 110 146 115 216.3 130 286.4 120 230.3 160 246.4 100 194.2 120 194.2 170 234.3 90 Copyright 2005 by Marcel Dekker. All Rights Reserved. as C 36 H 74 [55–57], strengthened the strictly logical view that macromolecules are a multiplication of smaller elements joined by covalent bonds. LDPE crystallizes in single lamellae with a thickne ss of 5.0 to 5.5 nm and a distance between lamellae of 7.0 nm which is filled by an amorphous phase. The crystallinity ranges from 58 to 62%. Recently, transition metals and organometallics have gained great interest as catalysts for the polymerization of olefins [58,59] under high pressure. High pressure changes the properties of polyethene in a wide range and increases the productivity of the catalysts. Catalyst activity at temperatures higher than 150  C is controlled primarily by polymerization and deactivation. This fact can be expressed by the practical notion of catalyst life time, which is quite similar to that used with free-radical initiators. The deactivation reaction at an aluminum alkyl concentration below 5  10 À5 mol/l seems to be first order reaction [60]. Thus for various catalyst-activator systems, the approximate polymerization times needed in a continuous reactor to ensure the best use of catalyst between 150 to 300  C are between several seconds and a few minutes. Several studies have been conducted to obtain Ziegler–Natta catalysts with good thermal stability. The major problem to be solved is the reduction of the transition metal (e.g., TiCl 3 ) by the cocatalyst, which may be aluminum dialkyl halide, alkylsiloxyalanes [60], or aluminoxane [59]. Luft and colleagues [61,62] investigated high-pressure polymerizat ion in the presence of heterogeneous catalysts consisting of titanium supported on magnesium dichloride or with homogeneous metallocene catalysts. With homogeneous catalysts, a pressure of 150 MPa (80 to 210  C) results in a productivity of 700 to 1800 kg PE/cat, molecular weights up to 110 000 g/mol, and a polydispersity of 5 to 10, with heterogeneous catalysts, whereas the productivity is 3000 to 7000 kg PE/cat, molecular weight up to 70 000 g/mol, and the polydispersity 2. B. Coordination Catalysts Ethene polymerization by the use of catalysts based on transition metals gives a polymer exhibiting a greater density and crystallinity than the polymer obtained via radical polymerization. Coordination catalysts for the polymerization of ethene can be of very different nature. They all contain a transition metal that is soluble or insoluble in hydrocarbons, supported by silica, alumina, or magnesium chloride [5,63]. In most cases cocatalysts are used as activators. These are organometallic or hydride compounds of group I to III elements; for example, AlEt 3 , AlEt 2 Cl, Al(i-Bu) 3 , GaEt 3 , ZnEt 2 , n-BuLi, amyl Na [64]. Three groups are used for catalysis: 1. Catalysts based on titanium or zirconium halogenides or hydrides in connection with aluminum organic compound (Ziegler catalysts) Table 2 Polymerization conditions and product properties of high-pressure polyethene (LDPE). Pressure (MPa) Temp. (  C) Regulator (propane) (wt%) Density (g/cm 3 ) Molecular weight MFI Distribution 165 235 1.6 0.919 1.3 20 205 290 1.0 0.915 17.0 10 300 250 3.9 0.925 2.0 10 Source: Ref. 29. Copyright 2005 by Marcel Dekker. All Rights Reserved. 2. Catalysts based on chromium compounds supported by silica or alumina without a coactivator (Phillips catalysts) 3. Homogeneous catalysts based on metallocenes in connection with aluminoxane or other single site catalysts such as nickel ylid, nickel diimine, palladium, iron or cobalt complexes. Currently, mainly Ziegler and Phillips catalysts as well as some metallocene catalysts [63] are generally used technically. Three different processes are possible: the slurry process, the gas phase process, and the solvent process [65–68]: 1. Slurry process. For the slurry process hydrocarbons such as isobutane, hexane, n-alkane are used in which the polyethene is insoluble. The polymer- ization temperature ranges from 70 to 90  C, with ethene pressure varying between 0.7 and 3 MPa. The polymerization time is 1 to 3 h and the yield is 95 to 98%. The polyethene produced is obtained in the form of fine particles in the diluent and can be separated by filtration. The molecular weight can be controlled by hyd rogen; the molecular weight distribution is regulated by variation of the catalyst design or by polymerization in several steps under varying conditions [69–73]. The best preparation takes place in stirred vessels or loop reactors. In some processes the polymerization is carried out in a series of cascade reactors to allow the variation of hydrogen concentration through the operating steps in order to control the distribution of the molecular weights. The slurry contains about 40% by weight polymer. In some processes the diluent is recovered after centrifugation and recycled without purification. 2. Gas phase polymerization. Compared to the slurry process, polymerization in the gas phase has the advantage that no diluent is used which simplifies the process [74–76]. A fluidized bed that can be stirred is used with supported catalysts. The polymerization is carried out at 2 to 2.5 MPa and 85 to 100  C. The ethene monomer circulates, thus removing the heat of polymerization and fluidizing the bed. To keep the temperature at values below 100  C, gas conversion is maintained at 2 to 3 per pass. The polymer is withdrawn periodi- cally from the reactor. 3. Solvent polymerization. For the synthesis of low-molecular-weight poly- ethene, the solvent process can be used [77,78]. Cyclohexane or another appropriate solvent is heated to 140 to 150  C. After addition of the catalyst, very rapid polymerization starts. The vessel must be cooled indirectly by water. Temperature control is also achieved via the ethene pressure, which can be varied between 0.7 and 7 MPa. In contrast to high-pressure polyethene with long-chain branches, the polyeth ene produced with coordination catalysts has a more or less linear structure (Figure 1) [79]. A good characterization of high-molecular-weight-polyethenes gives the melt rheological behaviour [80] (shear viscosity, shear compliance). The density of the homopolyethenes is higher but it can be lowered by copolymerization. Polymers produced with unmodi- fied Ziegler catalysts showed extremely high molecular weight and broad distribution [81]. In fact, there is no reason for any termination step, except for consecutive reaction. Equations (8) to (11) show simplified chain propagation and chain termination steps [11]. Copyright 2005 by Marcel Dekker. All Rights Reserved. Chain propagation: ð8Þ Chain termination: (a) By b elimination with H transfer to monomer ð9Þ (b) By hydrogenation ð10Þ Figure 1 Comparison of various polyethenes. Copyright 2005 by Marcel Dekker. All Rights Reserved. (c) By b elimination forming hydride ð11Þ Termination via hydrogenation gives saturated polymer and metal hydride. The termination of a growing molecule by an a-elimination step forms a polymer with an olefinic end group and a metal hydride. In addition, an exchange reaction with ethene forming a polymer with an olefinic end group and an ethyl metal is observed. 1. Titanium Chloride-Based Catalysts The first catalyst used by Ziegler et al. [5,82] for the polymerization of ethene was a mixture of TiCl 4 and Al(C 2 H 5 ) 3 , each of which is soluble in hydrocarbons. In combination they form an olive-colored insoluble complex that is very unstable. Its behavior is very sensitive to a number of experimental parameters, such as Al/Ti ratio, temperature and time of mixing of all components, and absolute and relative concentrations of reactants [83]. After complexation, TiCl 4 is reduced by a very specific reduction process. This reduction involves alkylation of TiCl 4 with aluminum alkyl molecules followed by a dealkylation reduction to a trivalent state: Complexation: TiCl 4 þAlEt 3 Ð TiCl 4 Á AlEt 3 ð12Þ Alkylation: TiCl 4 :AlEt 3 Ð EtTiCl 3 Á AlEt 2 Cl ð13Þ Reduction: 2EtTiCl 3 Ð 2TiCl 3 þ Et 2 ð14Þ Under drastic conditions, TiCl 3 can be reduced to TiCl 2 in a similar way. The actual TiCl 3 product is a compound alloyed with small amounts of AlCl 3 and probably some chemisorbed AlEt 2 Cl. The mechanistic process is very complex and not well understood. Instead of Al(C 2 H 5 ) 3 , also Al(C 2 H 5 ) 2 Cl, Al 2 (C 2 H 5 ) 3 Cl 3 , or Al(i-Bu) 3 could be used. These systems, called first-generation catalysts, are used for the classic process of olefin polymerization. In practice, however, the low activity made it necessary to deactivate the catalyst after polymerization, remove the diluent, and then remove the residues of catalyst with HCl and alcohols. This treatment is followed by washing the polyethene with water and drying it with steam. Purification of the diluent recover ed and feedback of the monomer after a purification step involved further complications. The costs of these steps reduced the advantage of the low-pressure polymerization process. Therefore, it was one of the main tasks of polyolefin research to develop new catalysts (second generation catalysts) that are more active, and can therefore remain in the polymer without any disadvantage to the properties (Table 3) [84]. The process is just as sensitive to perturbation, it is cheaper, and energy consumption as well as environmental loading are lower. It is also possible to return to the polymerization vessel diluent containing a high amount of the aluminum alkyl. The second generation is based on TiCl 3 compounds or supported catalysts MgCl 2 /TiCl 4 /Al(C 2 H 5 ) 3 or CrO 3 (SiO 2 ) (Phillips). Copyright 2005 by Marcel Dekker. All Rights Reserved. 2. Unsupported Titanium Catalysts There is a very large number of different combinations of aluminum alkyls and titanium salts to make high mileage catalysts for ethene polymerization, such as a-TiCl 3 þ AlEt 3 , AlEt 2 Cl, Al(i-Bu) 3 , and Ti(III)alkanolate-chloride þ Al(i- hexyl ) 3 [85]. TiCl 3 exists in four crystalline modifications, the a, b, g, and d forms [86]. The composition of these TiCl 3 s can be as simple as one Ti for as many as three Cl, or they can have a more complex structure whereby a second metal is cocrystallized as an alloy in the TiCl 3 . The particu lar method of reduction determines both composition and crystalline modification. a-TiCl 3 can be synthesized by reduction of TiCl 4 with H 2 at elevated temperatures (500 to 800  C) or with aluminum powder at lower temperatures (about 250  C); in this case the a-TiCl 3 contains Al cations [87]. More active are g- and d-TiCl 3 modifications. They are formed by heating the a-TiCl 3 to 100 or 200  C. The preferred a-TiCl 3 contains Al and is synthesized by reducing TiCl 4 with about 1/3 part AlEt 3 or 1 part AlEt 2 Cl. A modem TiCl 3 catalyst has a density of 2.065 g/cm 3 , a bulk density of 0.82, a specific surface area (BET) of 29 m 2 /g, and a particle size of 10 to 100 mm. The polymerization activity is in the vicinity of 500 L mol À1  s À1 [88]. 3. Supported Catalysts MgCl 2 /TiCl 4 catalysts. Good progress in increasing the polymerization activity was made with the discovery of the MgCl 2 /TiCl 4 -based catalysts [89]. Instead of MgCl 2 , Mg(OH)Cl, MgRCl, or MgR 2 [90–94] can be used. The polymerization activity goes up to 10 000 L mol À1 s À1 . At this high activity the catalyst can remain in the polyethene. For example, the specific volume (BET) of the catalystis 60 m 2 /g [95]. The high activity is accomplished by increasing the ethene pressure. The dependence is not linear as it was for first-generation catalysts, and the morphology is also different. The polyethene has a cobweb-like structure, whereas first generation catalysts pro duced a worm-like structure [90,91]. The cobweb structure is caused by the fact that polymerization begins at the surface of the catalyst particle. The particle is held together by the polymer. W hile polymerization is in progress, the particle grows rapidly and parts of it break. Cobweb structures are formed by this fast stretching process of the polyethene. Table 3 Comparison of various catalyst processes for ethene polymerization. First generation Second generation Catalyst preparation Catalyst preparation Polymerization Polymerization Limited influence to molecular weight and weight distribution Great variation of molecular weight and weight distribution Catalyst deactivation with alcohol Filtration Filtration Washing with water (HCl), wastewater treatment, purification, and drying of diluent Feedback of diluent Drying of PE Drying of PE Finishing Finishing Thermal degradation of molecular weight, blending Stabilization Stabilization Source: Ref. 84. Copyright 2005 by Marcel Dekker. All Rights Reserved. [...]... 1: 5 1: 300 30 30 15 20 20 70 20 50 80 16 0 80 20 20(80) 20 Refs 40–200 11 7 2000 11 7 7–45 11 8 35 000 >15 000 11 0 200 >5 000 11 9 400 000 >10 000 12 0 18 0 12 1 13 12 2 2.0 0.6 0.3 12 3 15 0 12 1 8  10 À3 (0.2) 12 4 ,12 5 0.4 12 4 ,12 5 complexing and dissociation, ðC5 H5 Þ2 TiRCl þ AlRCl2 Ð ðC5 H5 Þ2 TiRCl Á AlRCl2 ð22Þ ðC5 H5 Þ2 TiRCl Á AlRCl2 Ð ½ðC5 H5 Þ2 TiRCl3 Šþ þ ½AlRCl3 ŠÀ ð23Þ could be the active species of polymerization... copolymerization reactions The simplest kinetic scheme of binary copolymerization in the case of olefin insertion reaction is k 11 CatÀM1 polymer þ M1 À CatÀM1 ÀM1 polymer ! k12 CatÀM1 polymer þ M2 À CatÀM2 ÀM1 polymer ! k 21 CatÀM2 polymer þ M1 À CatÀM1 ÀM2 polymer ! k22 CatÀM2 polymer þ M2 À CatÀM2 ÀM2 polymer ! r1 ¼ k 11 k12 r2 ¼ k22 k 21 ð32Þ ð33Þ ð34Þ ð35Þ ð36Þ where k 11 and k22 are the homopolymerization... Copolymerization of ethene (M1) with various comonomers (M2) Comonomer Propene 1- Butene Isobutylene Styrene Vinyl acetate Vinyl chloride Acrylic acid Acrylic acid methylester Acrylnitrile Methacrylic acid Methacrylic acid methylester r1 r2 Pressure (MPa) Temp ( C) 3.2 3.2 2 .1 0.7 1 0 .16 0.09 0 .12 0. 018 0 .1 0.2 0.62 0.64 0.49 1 1 1. 85 10 2 17 0 10 2 17 0 10 2 17 0 15 0–250 11 0 19 0 30 19 6–204 82 265 204 82 12 0–220... Temp ( C) r1(Ml) r2(M2) r1 Á r2 Ref VCl4 VCl4 VOCl3 V(acac)3 VOCl2(OEt) VOCl2 VO(OBu)3 VO(OEt)3 VO(OEt)3 AlEt2Cl Al-i-Bu2Cl Al-i-Bu2Cl Al-i-Bu2Cl Al-i-Bu2Cl Al-i-Bu2Cl Al-i-Bu2Cl Al-i-Bu2Cl AlEt2Cl 21 3.0 20.0 16 .8 16 .0 16 .8 18 .9 22.0 15 .0 26.0 0.073 0.023 0.052 0.04 0.055 0.069 0.046 0.070 0.039 0.23 0.46 0.87 0.64 0.93 1. 06 1. 01 1.04 1. 02 19 2 19 3 19 2 19 3 19 4 19 4 19 4 19 4 19 5 a Monomer 1 ¼ ethene,... 204 82 12 0–220 13 0–220 13 0–220 10 0–280 200–240 70 14 0–226 15 0 15 0 16 0–200 15 0 13 4 17 polymerization permits the use of low polymerization temperatures and pressures Poly(ethylene-co-vinyl acetate, for instance, is produced at 10 0  C and 14 to 40 MPa [18 3] For the polymerization of ethene with vinyl acetate and vinyl chloride, emulsion polymerization in water is particularly suitable The polymerizates... than the homopolymer Due to thee short branching from Copyright 2005 by Marcel Dekker All Rights Reserved Table 8 Reactivity ratios of ethene with various comonomers and heterogeneous TiCl3 catalyst by 70  C Comonomer Cocatalyst r1 r2 Ref Propene Propene 1- Butene 4-Methyl -1- pentene Styrene Al(C6H13)3 AlEt3 AlEt3 AlEt2Cl AlEt3 15 .7 9.0 60 19 5 81 0 .11 0 .10 0.025 0.0025 0. 012 17 4 17 4 17 8 17 7 17 9 Table... propagation rates for monomers M1 and M2 and k12 and k 21 are cross-polymerization rate constants The definition of reactivity ratios is d½M1 Š ½M1 Šr1 ½M1 Š þ ½M2 Š ¼ d½M2 Š ½M2 Š½M1 Š þ r2 ½M2 Š ð37Þ The product r1  r2 usually ranges from zero to 1 When r1  r2 ¼ 1, the copolymerization is random As r1  r2 approaches zero, there is an increasing tendency toward alternation 1 Radical Copolymerization At elevated... 50 1. 9 2.2 2.6 3.4 2.0 3.0 3 .1 7.0 6.4 7 .1 . 11 7 Cp 2 TiCl 2 /AlMe 2 Cl/H 2 O 1: 6:3 30 2000 11 7 Cp 2 TiCl 2 /AlEt 2 Cl 1: 2 15 7–45 11 8 Cp 2 TiMe 2 /MAO 1: 10 5 .5  10 2 20 35 000 > ;15 000 11 0 Cp 2 TiMe 2 /MAO 1: 100 20 200 >5 000 11 9 Cp 2 ZrCl 2 /MAO 1: 1000 70. polymerization temperature (  C) (H 3 C) 3 -COOC(CH 3 ) 3 14 6.2 19 0 17 4.2 11 0 14 6 11 5 216 .3 13 0 286.4 12 0 230.3 16 0 246.4 10 0 19 4.2 12 0 19 4.2 17 0 234.3 90 Copyright 2005 by Marcel Dekker. All Rights. > ;10 000 12 0 VO(acac) 2 /Et 2 AlCl/activator 1: 50 20 18 0 12 1 Cp 2 VCl 2 /Me 2 AlCl 1: 5 50 13 12 2 Zr(allyl) 4 80 2.0 Hf(allyl) 4 16 0 0.6 Cr(ally) 3 80 0.3 12 3 Cr(acac) 3 /EtAlCl 1: 300 20 15 0 12 1 Ti(benzyl) 4 20(80)