Poly(propenonitrile), usually known as polyacrylonitrile, is manufactured from propene via propenonitrile (acrylonitrile). It is very widely used in co-polymers, particularly in fabrics and when materials need to be made hard and shock proof.
Uses of poly(propenonitrile) (polyacrylonitrile)
Poly(propenonitrile) itself is a very harsh fibre, rather like horse hair. An almost pure homopolymer is used when a very tough fabric is needed, for example for awnings, a soft top of a car or in brake linings. It is even used to reinforce concrete and in road construction. However, the vast majority of the polymer is co-polymerized. Although these co-polymers often contain more than 85% of propenonitrile units, they are much softer. The fibres formed from them are known as 'acrylic' fibres.
Two of the most used acrylic fibres are formed from the co-polymerization of propenonitrile with ethenyl ethanoate (vinyl acetate) and propenonitrile with methyl propenoate (methyl acrylate). The former is often mixed with cotton fibres to produce a light fabric, used in women's clothes. The latter is often used with wool (Figure 1).
Other co-polymers of propenonitrile include those when the co-monomer is methyl 2-methylpropenoate (methyl methacrylate) and with 1,1-dichloroethene.
With 1,1-dichloroethene as the co-monomer, a block co-polymer is formed which is fire-resistant and is often used in children's clothing.
An increasing use of poly(propenonitrile) co-polymers is in producing carbon fibres. If fibres of the polymer are heated under strictly controlled conditions the resulting fibres have remarkable strength.
Annual production of propenonitrile (acrylonitrile)
(a) The monomer
Propenonitrile (acrylonitrile), the monomer, is manufactured from propene. The alkene is mixed with ammonia and oxygen (from air) (1:1:2 volume ratio) and passed over a mixture of bismuth(III) and molybdenum(VI) oxides (Unit 2):
As it is a very exothermic reaction, and the temperature must be controlled at ca 600 K, a fluidized bed reactor (Unit 3) is used.
A small amount of hydrogen cyanide (3-6%) is also formed, which can be used in the manufacture of methyl 2-methylpropenoate.
The process has been modified, in Japan, to use propane as the feedstock. It will become particularly important if propane becomes much cheaper than propene. The catalyst used is based on vanadium(V) and antimony(III) oxides.
(b) The polymer
The polymer is manufactured by radical polymerization initiated by either a peroxide or by a mixture of potassium peroxydisulfate, K2S2O8 and a reducing agent such as potassium hydrogensulfite, KHSO3.
Figure 3 The soft tops for high quality cars are produced from almost pure homopolymer.
Polymerization takes place as for the homopolymer, a radical polymerization. The two monomers are mixed prior to addition of the initiator. When, ethenyl ethanoate is used as the co-polymer, polymerization is initiated with small amounts of potassium hydrogensulfite and potassium peroxodisulfate which get incorporated into the co-polymer, giving it sites which can bind to colorants and make them fast. Alternatively, a small amount of a third monomer containing, for example a sulfonic acid group, serves the same purpose.
The co-polymer contains a more or less regular alternation of the individual monomers, an example of an alternating co-polymer.
Similar procedures are used when other co-monomers are used.
With methyl propenoate and methyl 2-methylpropenoate, block co-polymers are produced:
An alternating polymer is produced with 1,1-dichloroethene as the co-monomer.
Date last amended: 7th October 2013