The kinetics of polysulphone formation IV. The isomerization of cis - and trans -2-butene accompanying polysulphone formation

Abstract

It has been shown by infra-red spectroscopic measurements that, at temperatures near the ‘ceiling temperature’, the copolymerization of sulphur dioxide with either cis - or trans -2- butene is accompanied by the geometrical isomerization of the 2-butene. The results of some kinetic studies of this latter reaction, using a vapour-pressure technique, are reported. Over the range investigated (25 to 60°C inclusive) the rate of this isomerization reaction increases with temperature according to the normal Arrhenius law, the overall energies of activation using benzoyl peroxide as the initiator being 16·5 ± 0·6 kcal mole –1 for the cis to trans isomerization and 18∙3 ± 0∙4 kcal mole –1 for the trans to cis isomerization. Prolonged reaction leads to the attainment of cis-trans equilibrium, and the value of the relevant thermodynamic functions are cis -2-butene→ trans -2-butene; in liquid sulphur dioxide, x B = 0∙09; ∆ H = – 1∙43 ± 0∙25 kcal mole –1 , ∆ S = – 2∙8 ± 0∙8 cal deg –1 mole –1 . These values differ from the values for an ideal liquid mixture of the cis - and trans -2-butenes. At 100°C and at high catalyst concentrations an additional isomerization reaction is detect­able; namely, that of formation of 1-butene by double-bond migration. The geometrical isomerization data are entirely consistent with the conclusion that the polymers formed from cis - and trans -2-butene are stereoisomeric (see also part III) and that one form of addition in the propagation step has a slightly lower energy of activation than the other.