In particular, n is from 1 to 5, preferably about 2.Suitable sulphonamide groups for Y include those of formula --N(R.sup.7)SO.sub.2 where R.sup.7 is hydrogen or alkyl such as C.sub.1-4alkyl, in particular methyl or ethyl.In a preferred embodiment, the compound of formula (I) is a compound of formula (II) CH.sub.2.dbd.CH--R.sup.5 (II) where R.sup.5 is as defined above in relation to formula (I).In