Synthesis of precision poly(1,3‐bicyclo[1.1.1]pentane alkylene)s via acyclic diene metathesis polymerization

Abstract

1,3-Disubstituted bicyclo[1.1.1]pentane (BCP) is a rigid, linear, non-conjugated hydrocarbon unit that is usually transformed from [1.1.1]propellane. This unit has been introduced into drugs as mimics of 1,4-disubstituted benzene moieties and used as rigid linkers in small-molecule materials. However, the influence of this unique structure on the polymer properties has only been scarcely investigated. In this work, three symmetrical α,ω-diene monomers containing one and two BCP units were synthesized for the first time from [1.1.1]propellane. Three types of precise poly(1,3-bicyclo[1.1.1]pentane alkylene)s with BCPs located on every 11th and 21st chain carbons were obtained via acyclic diene metathesis (ADMET) polymerization and subsequent hydrogenation. All these polymers show higher thermal stability than linear polyethylene. For polymers containing one BCP moiety in their repeating unit, BCP acts as a defect to distort the PE crystals and decrease the melting temperature of PE. However, the polymer that containing a [2]staffane moiety (two jointed BCP units) in the polymer backbone forms a new crystalline morphology. This work elucidates the impact of BCP units on the thermal and crystallization behavior of PE, providing new insights of utilizing BCP unit to construct new polymer backbone, regulate the packing order of polymers and their properties.