Synthesis of ring‐shaped polyisoprene

Cyclization of α,ω;‐dilithiopolyisoprenes has been achieved in hexane solution in the presence of tetrahydrofuran (15% in volume) at −40 to ‐ 50°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 α,ω;‐dilithiopolystyrenes or α,ω;‐disodiopolystyrenes and are attributed mainly to the presence, in the polyisoprene case, of predominant cyclic aggregates even at low organolithium concentration.