Macrocyclization of polymers via ring‐closing metathesis and azide/alkyne‐“click”‐reactions: An approach to cyclic polyisobutylenes

The end‐to‐end cyclization of telechelic polyisobutylenes (PIB's) toward cyclic polyisobutylenes is reported, using either ring‐closing metathesis (RCM) or the azide/alkyne‐“click”‐reaction. The first approach uses bisallyl‐telchelic PIB's ( M n = 1650, 3680, 9770 g mol −1 ) and Grubbs 1st‐, 2nd‐, and 3rd‐generation catalyst leading to cyclic PIB's in 60–80% yield, with narrow polydispersities ( M w / M n = 1.25). Azide/alkyne‐“click”‐reactions of bisalkyne‐telechelic PIB's ( M n = 3840 and 9820 g mol −1 ) with excess of 1,11‐diazido‐undecane leads to the formation of mixtures of linear/cyclic PIB's under formation of oligomeric cycles. Subsequent reaction of the residual azide‐moieties in the linear PIB's with excess of alkyne‐telechelic PEO enables the chromatographic removal of the resulting linear PEO‐PIB‐block copolymers by column chromatography. Thus pure cyclic PIB's can be obtained using this double‐“click”‐method, devoid of linear contaminants.