Polymerisation of Ethylene

In the 1950s, two chromium-based eatalysts, Ziegler-Natta and Phillips, were introdueed for use in polymerisation reaetions. The Phillips eatalyst is part of the industrial development of polyethylene and is still in use today. Using these eatalysts as a template, researehers are developing chromium-based catalysts for the polymerisation of monomers other than ethene, including the formation of polycarbonates from epoxides and carbon dioxide. 

Continuing with this study, Delley et investigated CO-reduced Phillips catalyst to study the initial bond formation that occurs during the initiation step of ethene polymerisation. Published literature has included much debate about the initial bond formation, stating that it could result, for example, via C-H or bond activation of ethene or silanol, re- 

The FT-IR analysis showed that SiH4-modified catalysts generated PE at a rate about seven times faster than that of the standard Phillips catalyst. Both catalysts were exposed to ethene (at low pressure) for eight minutes at room temperature, during which time operando FT-IR was collected. It was 

OH-region of the transmission IR spectra of CO-reduced Phillips catalyst before (a) and after treatment with C2H4 (b) or C2D4 (c), respectively. The insert (d) shows the OD-region of the IR spectrum of CO-reduced Phillips catalyst treated with C2D4. 

Reprinted with permission from Springer Science and Business Media.  

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CgH BiBr2, and diphenylbromobismuthine [39248-62-9] C22H2QBiBr, respectively, with lithium aluminum hydride or sodium borohydride at low temperatures yielded only black polymeric substances of empirical formula C H Bi (33). It has been claimed (34) that dimethylbismuthine and diphenylbismuthine can be used as cocatalysts for the polymerisation of ethylene (qv), propylene (qv), and 1,3-butadiene. The source of these bismuthines, however, was not mentioned. 

Higher hydrocarbons are formed by the polymerisation of ethylene. Any higher unsaturated hydrocarbons present are converted to the corresponding alcohols by hydration. 

Commercially, polyethylene is produced from ethylene, the polymer being produced by this route in March 1933 and repotted verbally by Fawcett in 1935. The basic patent relating to the polymerisation of ethylene was applied for by ICI on 4th February 1936 and accepted on 6th September 1937. 

Although in principle the high-pressure polymerisation of ethylene follows the free-radical-type mechanism discussed in Chapter 2 the reaction has two particular characteristics, the high exothermic reaction and a critical dependence on the monomer concentration. 

Controlled polymerisation of ethylene oxide under alkaline conditions will produce a range of polymers marketed under the trade name Carbowax. These have molecular weights in the range 1500-20000 and are greases or waxes according to their degree of polymerisation. Lower molecular weight polymers... 

This polymer, which has the structure [—CH2CH(CH3)—] arose as a commercial material following the work of Natta on catalysts for the preparation of high relative molar mass polymers from alkenes. Following his work on the polymerisation of ethylene, Natta showed in 1954 that it was possible to prepare analogous polymers of propylene. Commercial exploitation followed rapidly, and poly (propylene) was first marketed in 1957. 

Numerous accidents have brought about a violent polymerisation of ethylene. In two examples the conditions were the following ... 

Another study drew a comparison between the polymerisation of ethylene oxides and propylene oxides in similar operating conditions and in the presence of 10% of sodium hydroxide. When the polymerisation reached its maximum speed, the temperature reached 439°C for the former and 451 °C for the latter the pressures obtained are 44.6 and 26.6 bar respectively. 

The risks related to the polymerisation of ethylene halogen derivative are... 

Polymerisation of ethylene in presence of metallic copper becomes violent above a pressure of 54 bar at about 400°C, much carbon being deposited. 

Freeder, B. G. et al., J. Loss Prev. Process Ind., 1988, 1, 164-168 Accidental contamination of a 90 kg cylinder of ethylene oxide with a little sodium hydroxide solution led to explosive failure of the cylinder over 8 hours later [1], Based on later studies of the kinetics and heat release of the poly condensation reaction, it was estimated that after 8 hours and 1 min, some 12.7% of the oxide had condensed with an increase in temperature from 20 to 100°C. At this point the heat release rate was calculated to be 2.1 MJ/min, and 100 s later the temperature and heat release rate would be 160° and 1.67 MJ/s respectively, with 28% condensation. Complete reaction would have been attained some 16 s later at a temperature of 700°C [2], Precautions designed to prevent explosive polymerisation of ethylene oxide are discussed, including rigid exclusion of acids covalent halides, such as aluminium chloride, iron(III) chloride, tin(IV) chloride basic materials like alkali hydroxides, ammonia, amines, metallic potassium and catalytically active solids such as aluminium oxide, iron oxide, or rust [1] A comparative study of the runaway exothermic polymerisation of ethylene oxide and of propylene oxide by 10 wt% of solutions of sodium hydroxide of various concentrations has been done using ARC. Results below show onset temperatures/corrected adiabatic exotherm/maximum pressure attained and heat of polymerisation for the least (0.125 M) and most (1 M) concentrated alkali solutions used as catalysts. 

Ethylene sulfite is prepared from ethylene oxide, pyridine, and sulfur dioxide in excess to prevent polymerisation of ethylene oxide. Use of a deficiency of sulfur dioxide led to rupture of a reactor from that cause. 

A drum of crude product containing unreacted propylene oxide and sodium hydroxide catalyst exploded and ignited, probably owing to base-catalysed exothermic polymerisation of the oxide [1]. A comparative ARC study of the runaway exothermic polymerisation of ethylene oxide and the less reactive propylene oxide in presence of sodium hydroxide solutions, as typical catalytically active impurities, has been done. The results suggest that the hazard potential for propylene oxide is rather less than that for the lower homologue, though more detailed work is needed to quantify the difference [2],... 

The low-density polyethylene and polypropylene cases. In the course of the radical chain polymerisation of ethylene two kinds of transfer on the polymer play a major role, giving rise to LCB or SCB. These are illustrated in Figure 21. 

Figure 21 Transfer reactions in radical chain polymerisation of ethylene.

A major characteristic of the Phillips process chain polymerisation of ethylene is that it leads to very limited branching. The resulting polymer is thus highly linear and can reach high levels of crystallinity, hence high densities approaching 0.96-0.97. Such a polyethylene is known as HDPE for "High-density polyethylene". 

Examples of gas phase polymerisation are the polymerisation of ethylene and /7-xylene. 

Low density polyethylene (LDPE) can be produced by the high pressure polymerisation of ethylene, making use of oxygen Organisation and Qualities... 

The mechanism of the polymerisation of ethylene by Ziegler catalyst may be put as follows. (C2H5)3Al+TiCl 4 —> (C2H5)2A1C1+C 2H5 TiCl3... 

Catalyst systems consisting of reduced transition metal oxides on supports such as alumina or silica developed during 50s are of considerable importance for the polymerisation of ethylene. 

The transition metal acts as the active site and the chain growth step in polymerisation of ethylene can be represented as below ... 

Fig Growth step postulated for the polymerisation of ethylene by a soluble Ziegler-Natta catalyst. 

Detailed discussion of the energetics of the cationic polymerisation of ethylene shows that it cannot yield linear polymethylenes, in agreement with experiment. Since the cationic polymerisation of diazomethane does yield linear polymethylenes it cannot proceed through carbonium ions, as suggested by other workers. The following equations summarise the mechanism proposed here for this reaction ... 

The lack of isomerisation indicates that a non-ionic process is involved. The reaction does not continue to give a polymerisation of ethylene, because in contrast to the tertiary C-Cl bond which is broken, the primary C-Cl bond which is formed is too strong to be activated sufficiently by the A1C13. For the polymerisations involving an organic (monomer) halide and a metal halide, such as ZnBr2, it seems reasonable to represent the insertion also as occurring via a 6-membered cyclic transition state (II) ... 

Various Ln amides have already been described in Sections 4.3.5 and 4.3.6 as catalysts for polymerisation of ethylene," I38,i4i i43 jjex-l-ene, isoprene,styrene, " methyl methacrylate or other polar monomers such as t-butyl acrylate or acrylonitrile, . 138,143,152,177 nng-opening polymerisation catalysts for e-caprolactone or... 

A typical unimolecular reaction is the decomposition of organic peroxides for which always positive activation volumes of up to 15 cm3/mol have been observed. The decomposition of di(t-butyl)peroxide, an effective initiator for the high pressure polymerisation of ethylene, into two t-butoxyradicals, exhibits a positive activation volume of 13 cm3/mol (Table 3.2-1, a). When new bonds are formed as in the association... 

From the field desorption mass spectra of standard samples, a table for identification of poly(oxyethylene) alkylphenyl ethers and determination of the degree of polymerisation of ethylene oxide was constructed as shown in Table 6.1 n is the number of alkyl carbon atoms and m is the degree of polymerisation of ethylene oxide. When the field desorption mass spectrum having a peak pattern with the difference of 44m/z was obtained such as the peaks at 484, 528, 572, 616 and 660m/z, Table 6.1 would show that those peaks are due to poly(oxyethylene) nonylphenyl ethers with the degree of polymerisation of 6-10 of ethylene oxide. Table 6.2 also shows the identification of poly(oxyethylene) dialkylphenyl ethers and determination of the degree of polymerisation of ethylene oxide based on calculations of the molecular weight. 

E.g., higher aluminumtrialkyls are synthesised by the polymerisation of ethylene with triethylaluminum. At 90-120 °C and 4.5-12 MPa ethylene is stagewise attached to triethylaluminum, forming a complex mixture of higher aluminumtrialkyls ... 

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