SYNTHESIS OF RING-SHAPED POLYISOPRENE

Cyclization of alpha,omega-dilithiopolyisoprenes has been achieved in hexane solution in the presence of tetrahydrofuran (15% in volume) at -40 to -50-degrees-C. Using as linking agent the non-conjugated diene 1,2-bis(isopropenyl-4-phenyl)-ethane, macrocyclic polyisoprenes could be obtained with yields of at least 90%, even for molecular weights as high as 30 000 mol g-1. With SiCl4 as coupling agent no gelation occurred and yields of about 70% in cyclic dimers, probably bicyclic, have been observed. These results are compared to those obtained by various authors with alpha,omega-dilithiopolystyrenes or alpha,omega-disodiopolystyrenes and are attributed mainly to the presence, in the polyisoprene case, of predominant cyclic aggregates even at low organolithium concentration.