Efficient Synthesis and Cyclic Molecular Topology of Ultralarge-Sized Bicyclic and Tetracyclic Polymers

Cyclic polymers have been extensively studied because of their unique topology and physical properties, while the methods for efficient synthesis of well-defined bicyclic and multicyclic polymers are limited. Herein, an effective strategy was developed to synthesize ultralarge-sized bicyclic polymers by a ring-opening metathesis polymerization (ROMP)-based blocking-cyclization technique in a simplified feeding procedure, using the short ladderphane bearing four living ends as the initial motif. The molecular topology of the bicyclic polymer was clarified by pieces of evidence and validated by theoretical simulation. Importantly, the visualized eight-shaped molecular topology was observed. Meanwhile, the bicyclic polymer exhibited stronger thermal, fluorescence emission, and mechanical properties and better dielectric and energy storage performance than its four-arm counterpart, which elucidated the difference in molecular topology between bicyclic and four-arm polymers. Moreover, a tetracyclic polymer with a large ring size could be readily obtained. Therefore, this designed strategy opens new horizons for building bicyclic and multicyclic polymers using the conventional ROMP and commercial Grubbs catalyst.