Iron polymerisation

In addition, cyclodextrins incorporating a 2,6-bis(imino)pyridine unit have been used to support active iron polymerisation catalysts. Using the (i-cyclodextrin-based system 52, in the presence of a large excess of MAO, ethylene can be converted into HDPE (Fig. 16). Only low activities are, however, observed, which... 

The reluctance of acrylic monomers to polymerise in the presence of air has been made a virtue with the anaerobic acrylic adhesives. These are usually dimethacrylates such as tetramethylene glycol dimethacrylate. The monomers are supplied with a curing system comprising a peroxide and an amine as part of a one-part pack. When the adhesive is placed between mild steel surfaces air is excluded, which prevents air inhibition, and the iron present acts as a polymerisation promoter. The effectiveness as a promoter varies from one metal to another and it may be necessary to use a primer such as cobalt naphthenate. The anaerobic adhesives have been widely used for sealing nuts and bolts and for a variety of engineering purposes. Small tube containers are also available for domestic use. 

The use of steel reactors or containers to carry out reactions involving halogenous compounds can, by causing the formation of hydrogen chloride, and then iron chloride, provoke violent reactions of decomposition or polymerisation. 

In the same way, the detonation of moist trichloroethylene, which had been stored in a metal container, was explained by the hydrogen chloride formed. In this case it is possible to suggest another cause, which would involve iron trichloride forming by the interaction of hydrogen chloride with rust traces, and the catalysis by this salt of a polymerisation or degradation of the chlorinated derivative (see the similar case of aluminium chloride on p.281). 

In the presence of an acid (sulphuric acid, acetic acid) or a metal (iron) that plays a catalytic role, acetaldehyde gives rise to polymerisation reactions that are often violent and cause the compound to overflow. An accident of this type has also been observed with anhydrous formol at -189°C. 

The parameter most commonly monitored in this research is the extent of hydrogen peroxide decomposition. Measurement of tensile strength and/or the degree of polymerisation can be useful indicators of fibre damage. The effect of iron(III) ion concentration in accelerating the rate of peroxide decomposition is shown in Figure 10.23,... 

Impure material will polymerise readily in presence of trace metals (iron) or acids. 

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. 

A road tanker was loaded with l-chloro-2,3-epoxypropane and then driven 250 miles overnight to the delivery point. On arrival, the contents were found to have self heated (undoubtedly from polymerisation initiated by some unknown contaminant) to the boiling point (115°C at ambient pressure) and soon afterwards the relief valve lifted and discharged large volumes of vapour. Cooling with water sprays eventually restored thermal control over the remaining tanker contents [1]. The material is incompatible with strong acids, caustic alkalies, zinc, aluminium, aluminium chloride or iron(III) chloride, all of which catalyse exothermic polymerisation [2],... 

The chloride is usually (but not always) stabilised in storage by addition of aqueous alkali or anhydrous amines as acid acceptors. A 270 kg batch which was not stabilised polymerised violently when charged into a reactor. Contact of the chloride (slightly hydrolysed and acidic) with rust led to formation of ferric chloride which catalysed an intermolecular Friedel-Craft reaction to form polybenzyls with evolution of further hydrogen chloride. Contact of unstabilised benzyl chloride with aluminium, iron or rust should be avoided to obviate the risk of polycondensation. See Benzyl bromide Molecular sieve... 

Benzyl alcohol contaminated with 1.4% of hydrogen bromide and 1.1% of dissolved iron(II) polymerises exothermally above 100°C. Bases inhibit the polymerisation reaction. In a laboratory test, alcohol containing 1% of HBr and 0.04% of Fe polymerised at about 150° with an exotherm to 240° C. Formation and iron-catalysed poly-condensation of benzyl bromide seems to have been implicated. See Benzyl bromide Molecular sieve, or Catalytic impurities See Other BENZYL COMPOUNDS, POLYCONDENSATION REACTION INCIDENTS... 

Iron-Based and Cobalt-Based Olefin Polymerisation Catalysts... 

Keywords 2-6-Bis(arylimino)pyridine, Cobalt catalysts, Iron catalysts, Olefin polymerisation, Polyethylene... 

Fig. 1 Original iron and cobalt catalysts developed for ethylene polymerisation and oligomerisation [1, 2, 3, 4, 5, 6, 7]...

For more general overviews of post-metallocene a-olefin polymerisation catalysts, the reader is referred to a series of reviews [8, 9, 10, 11, 12], while recent reviews pertaining to the importance of 2,6-bis(imino)pyridines and to iron and cobalt systems per se have also been documented [13, 14],... 

The capacity of bis(arylimino)pyridine iron(II) (5) and cobalt(II) halides (6) to act as precatalysts for the polymerisation and oligomerisation of ethylene was first demonstrated when toluene solutions of 5 or 6 were treated with excess MAO... 

The introduction of metal alkyls to an MAO-activated bis(imino)pyridine iron catalyst has also been the subject of a number of studies. Both AlMe3 and AlEt3 have been added to 5a/MAO-based polymerisation catalysts leading to polyethylene displaying a bimodal distribution similar to that observed using 5a/M AO,... 

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