Synthesis And Phase Behavior Of Side-chain Liquid Crystalline Polymers Containing Long-alkyl Tail Triphenylene

Recently,the liquid crystalline mechanism of the triphenylene(TP)discotic side chain liquid crystal polymers(DSCLCPs)has attracted great attention.The research results showed that the formation of liquid crystalline phase for Tp DSCLCP was different from the ordinary rod-like SCLCPs.However,there are few studies to focus on the influence of the Tp-side-chain steric effect on the phase behavior of Tp DSCLCP.Therefore,we adopt an effective method to increase the intrinsic space volume via increasing the alkyl tail length of Tp.Through changing the kind of main chain and the length of spacer,the Tp steric effect can be tailored.The phase behaviors and phase structures of long alkyl tail Tp DSCLCPs were investigated by a combination of techniques,including DSC,POM,1D/2D WAXD,and SAXS.The main topics of this paper are as follows:1.A series of side-chain liquid crystalline polymers(SCLCPs)containing triphenylene mesogen,in which the long-alkyl tail Tp connected directly with main-chain,were synthesized successfully.The chemical structures of the monomers were confirmed by 1H NMR and mass spectrometry.The phase behaviors of polymers were investigated by a combination of techniques,including DSC,POM,1D/2D WAXD,and SAXS.The experimental results suggested that the type of main-chain played an important role in the LC phase structures of these polymers.Because of the steric effects of side-chains and the coupling effects between the Tp moieties and the main chains,all the polymers exhibited columnar phases.However,the SCLCPs with poly(vinyl benzene methyl ether)or polynorbornene backbone displayed hexagonal columnar phase,while those with polyacrylate or polymethacrylate backbone presented columnar nematic phase,and the one with poly(vinyl benzoate)main-chain showed rectangular columnar phase.Moreover,the clearing temperatures(Ti)changed with change in main-chain.Especially,the Ti of the SCLCP with polymethacrylate backbone was above 300 oC.2.Long-alkyl tail triphenylene(Tp)side-chain liquid crystalline polymers(SCLCPs)with different spacer length(denoted as P-m-TP,m=2,3,4,6,8,which is the spacer length)have been designed and synthesized.The chemical structures of the monomers were confirmed by 1H NMR and mass spectrometry.The phase behaviors of polymers have been investigated by a combination of techniques including DSC,POM,1D WXRD and SAXS.The experimental results revealed that the Tp stericeffect,decoupling effect and ?-? stacking effect were affected by the spacer length.When m=2,4,the polymers could form the column nematic(?N)phase at high temperature,while at low temperature,polymers presented rectangular column(?R)phase.When m=3,the polymer showed column nematic(?N)phase.In addition,the clearing temperatures(Ti)of those polymers were above 300 oC.All of those properties were similar to the mesogen-jacketed liquid crystalline polymers'.Those results implied that the steric effect could induce the column phase developed by the Tp moieties and the main chain as a whole although the spacer length exceeded 4.When m=6 and 8,the polymers displayed hexagonal columnar(?H)phase,resulting from the self-assemble of triphenylene due to decoupling effect and ?-? stacking effect.And Ti was 91 oC and 80 oC respectively,showing that the polymers produced the usual liquid crystalline behavior because decoupling effect and ?-? stacking effect overcame the steric effect.