Nitrile polymerisation

Acrylonitrile came into contact with silver nitrate and was kept in this way for a long time. It gave rise to a violent detonation thert was put down to nitrile polymerisation, which formed successive layers of pilymer at the surface of the salt particles the temperature rise that was caused accelerated the polymerisation gradually. 

The secondary amine that was used could be tetrahydrocarbazole or pyrol. The reaction was known and not mentioned as being dangerous. The authors of this new experiment used four times the amounts recommended in the method published. They also introduced the ionic compound at 0°C and stopped the cooling rapidly. These changes were sufficient to cause the medium to heat up and then detonate. It was considered to be due to the nitrile polymerisation caused by ammonium salt. 

Vmulsifier Type. The manufacturers of NBR use a variety of emulsifiers (most commonly anionic) for the emulsion polymerisation of nitrile mbber. When the latex is coagulated and dried, some of the emulsifier and coagulant remains with the mbber and affects the properties attained with the mbber compound. Water resistance is one property ia particular that is dependent on the type and amount of residual emulsifier. Residual emulsifer also affects the cure properties and mold fouling characteristics of the mbber. 

In the above examples the polymerisation takes place by the opening of a carbon-carbon double bond. It is also possible to open carbonyl carbon-oxygen double bonds and nitrile carbon-nitrogen triple bonds. An example of the former is the polymerisation of formaldehyde to give polyformaldehyde (also known as polyoxymethylene and polyacetal) (Figure 2.3). 

The common feature of these materials was that all contained a high proportion of acrylonitrile or methacrylonitrile. The Vistron product, Barex 210, for example was said to be produced by radical graft copolymerisation of 73-77 parts acrylonitrile and 23-27 parts by weight of methyl acrylate in the presence of a 8-10 parts of a butadiene-acrylonitrile rubber (Nitrile rubber). The Du Pont product NR-16 was prepared by graft polymerisation of styrene and acrylonitrile in the presence of styrene-butadiene copolymer. The Monsanto polymer Lopac was a copolymer of 28-34 parts styrene and 66-72 parts of a second monomer variously reported as acrylonitrile and methacrylonitrile. This polymer contained no rubbery component. 

Here is a list of all dangerous reactions that are related to nitrile functional group behaviour. By active polymerisation is meant the polymerisation that affects the carbon-nitrogen triple bond. Polymerisations that are related to an ethylene double bond will be dealt with on p.336. So far as stability is concerned, it is difficult to say whether certain spontaneous reactions of certain nitriles are... 

An old bottle (1 year) containing glycolonitrile with phosphoric acid used as a stabiliser showed the appearance of tars. It detonated during handling. The detonation was probably due to the polymerisation of nitrile that was made possible by the fact that phosphoric acid was isolated by tars. Besides, the cap was cemented by tars that had already formed round the cap. A similar accident happened thirteen days after distilling the same nitrile. 

The NFPA reactivity codes indicate the risks that are related to the propensity for polymerisation and/or instability of the nitrile group and of the potential ethylene double bond. The table below gives the available data with some contradictions between different sources, as usual (for acetonitrile, code 1 seems to make more sense)... 

The previous examples regarding nitrile-alcohols corresponded to this classification. However, since their danger is related to acrylonitrile polymerisation they were classified in the previous paragraph. The three examples below exclude this type of interpretation. 

A mixture of acetonitrile and sulfuric acid on heating (or self-heating) to 53°C underwent an uncontrollable exotherm to 160°C in a few seconds. The presence of 28 mol% of sulfur trioxide reduces the initiation temperature to about 15°C. Polymerisation of the nitrile is suspected. 

A year-old bottled sample, containing syrupy phosphoric acid as stabiliser and which already showed signs of tar formation, exploded in storage. The pressure explosion appeared to be due to polymerisation, after occlusion of inhibitor in the tar, in a container in which the stopper had become cemented by polymer [1], A similar pressure explosion occurred when dry redistilled nitrile, stabilised with ethanol [2], polymerised after 13 days [3], The spontaneous and violent decomposition of the nitrile on standing for more than a week is usually preceded by formation of a red polymer [4],... 

It may polymerise violently on heating at 130°C, or in contact with strong bases at lower temperatures [1], The stability of the molten nitrile decreases with increasing temperature and decreasing purity, but no violent decomposition below 100°C has been recorded [2], However, a partially filled drum of malononitrile stored in an oven at 70-80°C for 2 months exploded violently [3],... 

To catalyse the cyanoethylation of pyrrole, 3 drops of the basic catalyst solution were added to the reaction mixture of pyrrole (30%) in the nitrile. An exotherm developed and base-catalysed polymerisation of the nitrile accelerated to explosion. 

Cyanoethylation of 1,2,3,4-tetrahydrocarbazole initiated by the quaternary base had been effected smoothly on twice a published scale of working. During a further fourfold increase in scale, the initiator was added at 0°C, and shortly after cooling had been stopped and heating begun, the mixture exploded. A smaller proportion of initiator and very slow warming to effect reaction are recommended (to avoid rapid polymerisation of the nitrile by the base). 

Addition of sulfuric acid to the cyano-alcohol caused a vigorous reaction which pressure-ruptured the vessel [1]. This seems likely to have been caused by insufficient cooling to prevent dehydration of the alcohol to methaciylonitrile and lack of inhibitors to prevent exothermic polymerisation of the nitrile [2],... 

The name originally applied to all synthetic rubbers produced by the sodium polymerisation of butadiene it is derived from Bu for butadiene and Na for sodium. The name was subsequently used in various forms, e.g., Buna N for nitrile rubber or NBR, and Buna S for SBR. The tradename Perbunan (Bayer) is also derived from Buna. 

This is styrene-butadiene rubber polymerised at a temperature of 5 °C (41 °F) in contrast to the original polymerisation temperature of 50 °C (122 °F). It is also known as Low Temperature Polymer (LTP). Nitrile rubber can also be made by a low temperature process. Such polymers are characterised by improved processibility. 

A high polymer resulting from the polymerisation of a mixture of two different monomers styrene-butadiene mbber, butyl (isoprene-isobutylene) mbber and nitrile (acrylonitrile-butadiene) mbber are typical copolymers. 

Polymerisation of a monomer or mixture of monomers which have been emulsified with soap in water. SBR, neoprene and nitrile rubbers are manufactured by the emulsion polymerisation process. 

The rubber may be natural, in which case the latex is produced by the rubber tree. Latex of the main synthetic rubbers is produced by the technique of emulsion polymerisation. The term latex has been broadened in recent years and a general definition is now a stable dispersion of a polymeric substance in an aqueous medium . Latices may be classified as natural (from trees and plants), synthetic (by emulsion polymerisation) and artificial (by dispersion of the solid polymer in an aqueous medium). They may also be classified according to the chemical nature of the polymer, e.g., SBR, nitrile, polychloroprene, etc. 

Nitrile rubbers are copolymers of butadiene and acrylonitrile which are produced by emulsion polymerisation hot and cold polymerised types are available. The hot polymerised types generally have higher green strength and are slightly harder to process than cold copolymers. 

Polymerisation of HCN species is also possible once the initial monomers have been formed by the reactions with nitrogen HCN polymers have been postulated in many places in the solar system, from the clouds of Jupiter and Saturn to the dark colour of the surface of comet Halley, not to mention its possible role in the formation of the prebiotic molecule adenine. Photolysis of HCN produces CN and then the formation of nitrile polymers ... 

Pseudomonas chloraphis cells were used first, and more recently Rhodococcus rhodochrus Jl. Cells are immobilised in polyacrylamide particles and used in column reactors operated at below 10°C. The acrylamide is produced in 100% yield, and is so pure that polymerisation inhibitors have to be added to prevent spontaneous polymerisation. Both acrylonitrile and acrylamide inhibit the nitrile hydratase the nitrile hydratase is extremely stable. Therefore acrylonitrile is fed to maintain a level of 6% resulting in the accumulation of acrylamide of 66% (w/v), after which is it simply decolourised and concentrated (Yamada and Kobayashi, 1996). 

Mathias, E. et al., J. Chem. Soc., Chem. Comm., 1981, 569—570 Great caution is necessary when handling cone, solutions or the solvent-free nitrile. Phosphoric acid stabilises it to some extent, but sudden foaming polymerisation may occur. Gaseous decomposition products may burst the container, even when kept in refrigerated storage. 

Significantly endothermic AHf (1) 147 kJ/mole 2.8 kJ/g. The monomer is sensitive to light, and even when inhibited (with aqueous ammonia) it will polymerise exother-mally at above 200°C [1]. It must never be stored uninhibited, or adjacent to acids or bases [2]. Polymerisation of the monomer in a sealed tube in an oil bath at 110°C led to a violent explosion. It was calculated that the critical condition for runaway thermal explosion was exceeded by a factor of 15 [3]. Runaway polymerisation in a distillation column led to an explosion and fire [4]. Another loss of containment and fire resulted from acrylonitrile polymerisation in a waste solvent tank also containing toluene and peroxides (peroxides are polymerisation initiators) [5]. Use of the nitrile as a reagent in synthesis can lead to condensation of its vapour in unseen parts of the equipment, such as vent-pipes and valves, which may then be obstructed or blocked by polymer [6]. 

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