Styrene oligomerisation

Our studies have confirmed that the oligomerisation of styrene by perchloric acid is both chemically and kinetically simple. However, the reactions which follow completion of the polymerisation, and during which carbonium ions are formed and destroyed, are complicated. They can be rationalised in terms of equilibria involving ions, acid, double bonds, and esters cyclisation of olefinic oligomers and formation of polyenes by way of allylic ions add further complications. We have thus shown in some detail just why such systems must be treated with the greatest circumspection if they are to yield valid information. 

Carbocations such as t-butyl cation which are sufficiently electrophilic to react efficiently with styrene and linear dienes are themselves highly unstable and cannot be isolated as stable salts. They tend to oligomerise or react readily even with the most stable anions. Of course they can be generated in situ in a polymerisation reaction (1,95),... 

Hasegawa and Higashimura showed that perfluorinated resinsulphonic acid , Nafion-H, is an effective catalyst for the oligomerisation of styrene. 

Treatment of [CpTiCl(dmpe)2] with one equivalent of MeLi affords [CpTi(Me)(dmpe)2]. This complex is an active catalyst for the oligomerisation of ethene to but-l-ene, 2-ethylbut-l-ene and 3-methylpent-l-ene. The mechanism of the catalysis is proposed to involve titanacyclopentane intermediates. The complex [Cp TiMe2][MeB(C6Fj)3] acts as both a Ziegler-Natta catalyst for the polymerisation of alkenes, such as ethene and propene, and as a carbocationic initiator for the polymerisation of election rich alkenes such as A -vinylcarbazole and vinyl ethers. It also polymerises styrene to syndiotactic polystyrene, probably via a carbocationic initiated polymerisation. 50... 

---