Significantly Enhanced Thermotropic Liquid Crystalline Columnar Mesophases in Stereoregular Polymethylenes with Discotic Triphenylene Side Groups

Side-chain discotic liquid crystalline polymers (SDLCPs) with discotic (disclike) mesogens (discogens) attached as side groups through flexible spacers constitute a class of fascinating organic polymer semiconducting materials. While so far almost all reported SDLCPs belong to conventional C2 polymers based on polymerization of vinyl monomers, limiting their structure diversities, substitution density, and efficiency promotion. In this article we present the synthesis of a series of syndiotactic polymethylene SDLCPs of Pm(TPn) with discotic triphenylene (TP) side groups of variant peripheral alkoxy substituents (n = 6, 4, 10) and different length alkyl spacers (m = 3, 4, 6, 8, 10, 12) through an indirect two-step rhodium-complex-catalyzed C1 carbene polymerization pathway. The thermal properties and ordered organization structures of the precursor polymers and polymethylene SDLCPs have been systematically investigated with differential scanning calorimetry (DSC) and polarized optical microscopy (POM), especially through synchrotron radiation variable-temperature small/wide-angle X-ray scattering (SAXS/WAXS) analyses. All of the series C1-type syndiotactic polymethylenes with high densely substituted TP side groups exhibit various hierarchical ordered columnar mesophases comparable to that of the typical side-chain C2 polymers of well-defined polyacrylates with TP discogens. Moreover, they possess a remarkably broadened temperature range of columnar structures persistent to very high temperatures in virtue of the stiff helical polymethylene backbone. This work provides a feasible route to prepare the C1-type SDLCPs with high densely substituted functional side groups and may offer an in-depth understanding for the hierarchical organization of ordered columnar structures with significantly increased thermal stability.