Butyl rubber ,a synthetic rubber,is a copolymer of isobutylene and isoprene.It is also called isobutylene-isoprene rubber.It is based on homopolymer of isobutylene that is polyisobutylene(C4H8)n.Butyl rubber was first produced by William Sparks and Robert Thomas in 1937 at the Standard Oil Company(New Jersey).
Attempts are made to produce synthetic rubber,it involves polymerization of dienes such as isoprene and butadiene.Dienes are the hydrocarbon molecules containing two carbon-carbon double bonds.Both William Sparks and Robert Thomas define a convention by copolymerizing isobutylene with small amount of isoprene.Isoprene provide extra double bond which is required to cross link.Intially,Butyl rubber was called “futile butyl”.Later on it was widely accepted for its low permeability to gases and its excellent resistance to oxygen and ozone.
Isobutylene(C[CH3]2=CH2) is a hydrocarbon and is a four-carbon branched alkene.It is obtained from refinery streams by reaction with sulfuric acid.It is odorless and tasteless.Isobutylene and isoprene(CH2=C[CH3]-CH=CH2) are obtained by the thermal cracking of natural gas or of the lighter fraction of crude oil.
Isobutylene is a gas and isoprene is a volatile liquid at normal temperature.Butyl rubber is produced by polymerization of 98% of isobutylene with 2% of isoprene. Butyl rubber is produced by copolymerizing isobutylene in solution with low concentration of isoprene.Isobutylene is refrigerated to very low temperature and is diluted with methyl chloride.Reaction initiates on addition of low concentration of isoprene in the presence of aluminium chloride and as a result compounds copolymerizes.In copolymerization single unit molecules link together to form huge,multiple unit molecules.The polymer repeating units have following structures-
Butyl rubber which contains small amount of isoprene and because polyisobutylene’s pendant group are arranged in a regular order along the polymer chains and because the chains crystallize rapidly on stretching, it is strong as natural rubber.
RELATED QUESTIONS AND ANSWERS
Ans.-Dienes are the hydrocarbon molecules containing two carbon-carbon double bonds.Some of the dienes are-isoprene and butadiene.
Q2.Who produced Butyl rubber?
Ans.-Butyl rubber was produced by William Sparks and Robert Thomas at Standard Oil Company in New Jersey in 1937.
Q3.How Butyl rubber is prepared?
Ans.-It is prepared by copolymerizing about 98% of isobutylene with lo concentration that is 2% of isoprene.
Q4.What is copolymerization?
Ans.-In copolymerization single unit molecules link together to form huge,multiple unit molecules.