An Efficient Ring‐Closure Method for Preparing Well‐Defined Cyclic Polynorbornenes

An efficient bimolecular ring‐closure method is developed to prepare the well‐defined cyclic polynorbornenes by combining the living ring‐opening metathesis polymerization (ROMP) with the self‐accelerating double strain‐promoted azide–alkyne cycloaddition (DSPAAC) reaction. In this method, ROMP is used to synthesize the well‐defined linear polynorbornenes with both azide terminals by virtue of a N‐hydroxysuccinimide‐ester‐functionalized Grubbs initiator following the modification of polymer end groups. DSPAAC click reaction is then used to ring‐close the linear polymer precursors and prepare the corresponding well‐defined cyclic polynorbornenes using the sym‐dibenzo‐1,5‐cyclooctadiene‐3,7‐diyne (DIBOD) as small linkers. The self‐accelerating DSPAAC ring‐closing reaction facilitates this method to efficiently prepare pure cyclic polynorbornenes in the presence of a molar excess of DIBOD small linkers to the linear polynorbornene precursors. This is the first report to prepare well‐defined polynorbornenes with cyclic topology based on the ring‐closure strategy for cyclic polymers. An efficient bimolecular ring‐closure method is developed for the first time to specifically prepare well‐defined cyclic polynorbornenes based on the combination of living ring‐opening metathesis polymerization and self‐accelerating double strain‐promoted azide–alkyne cycloaddition click reaction.