Hierarchical Structures in a Main-Chain/Side-Chain Combined Liquid Crystalline Polymer with a Polynorbornene Backbone and Multi Benzene Side-Chain Mesogens

A series of main-chain/side-chain combined liquid crystalline polymers (MCSCLCPs) with a polynorbornene backbone and multi-benzene mesogens in the side chain, PNbnPP (n = 2, 6, 10), were synthesized through a controllable polymerization method: ring-opening metathesis polymerization (ROMP). Differential scanning calorimetry, polarized light microscopy, and one-/two-dimensional wide-angle X-ray diffraction were utilized to investigate the phase behavior of PNbnPP. Experimental results reveal that the two fundamentally different liquid crystalline (LC) building blocks the mesogen-jacketed LC polymer main chain and the multi-benzene calamitic mesogens in the side chain compete and promote with each other, leading to a complex phase behavior. Because of the coupling effect between the rigid core and the pendants (multi-benzene mesogens) of PNb2PP with a short spacer, PNb2PP forms a simple smectic phase. On the other hand, owing to the decoupling effect of the long spacers, at low temperatures PNb6PP and PNb1OPP form hierarchical structures, including the smectic phase of the polymer as a whole and the ordered packing of the multi-benzene mesogens.