Preparation And Properties Of Main Chain Liquid Crystal Polymer Based On Sulfur Fluoride Exchange Click Chemistry

As an important type of functional polymeric materials,liquid crystal polymers,in particular main-chain liquid crystal polymers?MCLCPs?,combining anisotropic molecular orders and the excellent mechanical properties of polymers,have prosperous applications in the engineering of plastics,gas separation membranes,thermal insulated materials,high-strength and high-modulus fibers,etc.In the past few decades,considerable efforts have been devoted to exploring new methods for the efficient synthesis and rapid screening of novel MCLCP materials.Click chemistry,since its first report in 2001,has been recognized as a highly efficient modular synthetic strategy for constructing complex molecules.Because of its vast technical advantages,click chemistry has gradually become one of the most powerful tools in the fields of organic synthesis,drug discovery,polymer modification and materials science and chemical biology.In recent years,several research groups have put a great deal of effort into introducing click chemistry for the preparation of MCLCPs,including thiol-ene polyaddition,thiol-yne polyaddition,and copper-catalyzed azide-alkyne cycloaddition?CuAAC?.However,the previous click synthetic routes all had to prepare liquid crystal monomers first and then linked liquid crystal monomers together to give the designed MCLCPs.In other words,the traditional click methods could only make one single MCLCP from the corresponding mesogenic monomer.In this work,four kinds of MCLCPs bearing sulfate esters groups were successfully synthesised from two orthogonal monomer groups via a new click chemistry named as Sulfur Fluoride Exchange Click Chemistry?SuFEx?.The main work is as follows:?1?One FO₂SO-functionalized monomer FM1 and four aryl silyl ether-containing monomers SiM1,SiM2,SiM3 and SiM4 were designed and synthesized by two or three steps reaction,and all of them show good thermal stabilities and tolerance to water and oxygen.In addition,the characterization of mesomorphic properties indicates that SiM1-3and FM1 all exhibited crystal phases,while SiM4 presented a nematic phase.?2?A SuFEx approach was applied in producing four MCLCPs PY1803,PY1804,PY1805 and PY1806 bearing sulfate esters groups for the first time.These MCLCP products were synthesised from two orthogonal monomer groups with a ratio of 1:1 in the presence of organic superbase catalysts.?3?The structures and thermal properties of these monomers and MCLCPs were examined by ¹H NMR,¹³C NMR,¹⁹F NMR,fourier transform infrared?FTIR?,gel permeation chromatography?GPC?and thermogravimetric analysis?TGA?.The mesomorphic properties of these MCLCPs were further studied by differential scanning calorimetry?DSC?,polarized optical microscope?POM?and wide-angle X-ray scattering?WAXS?.The experimental results show that the diverse MCLCP products containing new formed mesogenic cores in polymer main chains can be successfully synthesised via a new click chemistry called as SuFEx.Although most of the monomers exhibited crystal phases,their corresponding MCLCPs all show liquid crystal phases.PY1803 and PY1805 have a nematic phase with smectic fluctuation,while PY1804 and PY1806 show a nematic phase.All MCLCPs show high clearing point temperature and relatively wide liquid crystal interval.This SuFEx strategy might provide a new perspective for the efficient synthesis and rapid screening of novel MCLCP materials.