Polyisobutene manufacture

Isobutene has the distinction of having been the first alkene to have been polymerized to a high molecular weight polymer whilst the polymer was the first polyalkene to have been commercially developed. Whereas polyethylene was first prepared (unexpectedly) in 1933 with pilot plant production not commencing until the 1st September 1939, and polypropylene not discovered until the early 1950s, the IG Farben company were as early as 1932 disclosing details of polyisobutene manufacture to the Standard Oil Co under a research agreement. 

Isobutene is used in the field of elastomers, mainly to manufacture a special rubber, butyl rubber, by copolymerization with small amounts of isopiene. It serves essentially for the manufacture of inner tubes, but its production remains modest and accounts for barely 10 per cent of that of SBR (Styrene Butadiene Rubber). Isobutene is also used to produce additives for oils (polyisobutenes), detergents (di- and triisobutylenes) and cur rently for the manufacture of MTBE. 

It was noted in the previous chapter (Section 1.4.2.1.) that the polymerization of isobutene could be accomplished only with cationic initiators. Aluminium chloride and boron trifluoride are the preferred initiators for commercial processes the separate addition of a co-catalyst is not generally necessary and adventitious substances possibly fulfil this role. At ordinary temperatures polymerization is extremely rapid and leads to low molecular weight polymers which are viscous oils or sticky solids. However, at low temperature (—80 to — 100°C) high molecular weight material is produced. Even at these low temperatures the reaction is complete in a few seconds and it is necessary to have particularly efficient means of dissipating the heat evolved. Conventional batch processes are unsuitable and continuous processes are used in which only small quantities of reactants are involved at any one moment. In one process (Badische Anilin- Soda-Fabrik A. G.), solutions of isobutene and boron trifluoride in liquid ethylene are mixed on a moving belt so that the polymerizing system is in the form of a thin film and heat is removed by the vaporization of the solvent. The polymer is then mixed with an alkali or ethanol to deactivate the initiator and treated with steam to remove water-soluble contaminants. Another process for polyisobutene (Standard Oil Co. (N.J.) (U.S.A.)) follows closely the procedure outlined in Section 2.10.2. for the manufacture of butyl rubber. 

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