2-Methylbuta-1,3-diene--2-methylprop-1-ene (1/1)

BeschreibungA synthetic copolymer containing from 0.5 to 2.0 molar percent of isoprene, the remainder, respectively, consisting of isobutylene. It is prepared by copolymerization of isobutylene and isoprene in methyl chloride solution, using aluminum chloride as the catalyst. After completion of polymerization, the rubber particles aretreated with hot water containing a suitable food-grade deagglomerating agent, such as stearic acid. Finally, the coagulum is dried to remove residual volatiles.

VerwendenButyl rubber is formed from the polymerization of isobutene (isobutylene) with small amounts of chloroprene, isoprene, or butadiene and may be halogenated. The reaction is carried out in a closed system with an aluminum chloride catalyst. Butyl rubber is highly impervious to gases, which makes it the rubber best suited for inner tubes and tires, air chambers, adhesives, and dielectrics. Isobutene is an anesthetic and asphyxiant gas and can be hazardous in concentrations high enough to produce asphyxia. At these concentrations, explosion is an additional hazard.

synthetischeCommercial butyl rubbers generally contain 1-3 mole % isoprene. In a typical process, a solution of the monomers in methyl chloride is pre-cooled to -lOOC and then fed continuously into the base of a reactor together with a solution of aluminium chloride (initiator) in the same diluent. The reaction is highly exothermic and in order to maintain the temperature at -100C the reactor is fitted with a powerful stirrer and cooling coils containing liquid ethylene. The polymer forms as a granular slurry which is displaced continuously from the top of the reactor. The slurry passes into a flash tank where it is vigorously agitated with hot water. This treatment deactivates the initiator and extracts water-soluble products. At the same time the diluent and unreacted monomers are flashed off and are purified and re-used. Also at this point a lubricant and an antioxidant are introduced into the polymer. The lubricant, usually zinc stearate, prevents agglomeration of wet crumb and the antioxidant, usually phenyl-p-naphthylamine, reduces degradation during drying operations. The slurry then passes to a screen where wet polymer crumb is isolated. The crumb is dried at about 95-170C, fed through an extruder and then hot milled. The object of these last operations is to compact the polymer and remove all traces of residual water. In butyl rubber the isoprene is present as random l,4-units and the copolymer thus has the following form: