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Natural rubber can be vulcanised by sulphur. However butyl rubber, which is a
copolymercontaining isobutylene and isoprene units, requires very powerful accelerators
to be vulcanised.This project is an alternative procedure to effect cross-linking of butyl
rubber.It does not involve an accelerator and proceeds easily at room temperature in
solutionin an organic solvent using sulphur monochloride (S2Ch) as cross-linking agent.
Butylrubberhaving a low content of isoprene units was dissolved in toluene and various
amountsof S2Chwere added with stirring.
The effect of reaction time on conversion to insoluble cross-linked material was
examined and the gel was characterized with respect to the subsequent equilibrium
degree of swelling in organic solvents and with respect to elastic properties using
compressionstrain. The swelling capacity of the gels in toluene or cyclohexane increased
withdecreasingconcentration of sulphur monochloride. Cyclohexane found to be a better
solventthan toluene for swelling.
The swellingratio of the gels prepared at a fixed concentration of S2Ch first increased
rapidly with increasing swelling time, but then decreased until an equilibrium was
obtained,for gels prepared at medium - high concentrations of S2Ch. For those prepared
at low concentration of S2Ch swelling proceeded to an equilibrium level which remain
constant.
Thisunusualswelling behaviour was accompanied with an increase of the elastic moduli
of the gels during the swelling process. The results were explained with the post crosslinkingreactionstaking place during the swelling process of PIB gels.
lncreasescontent of isoprene in the butyl rubber gave site to corresponding increases in
effectivecross-linking density, elastic moduli, and polymer solvent interaction parameter.
Theweightfraction of solvent become high when the butyl rubber contains less isoprene
units
