Synthesis And Dielectric Properties Of The Functional Side-chain Liquid Crystal Polymer

LCP materials have attracted extensive attention and research due to their excellent electrical and optical properties.In recent years,5G communication technology has developed rapidly,and LCPs with low dielectric constant and low dielectric loss have attracted great attention in the industry as ideal materials for 5G antennas.However,the physical anisotropy of liquid crystal polymer films tends to occur during the processing process,which restricts their development and application.In this paper,a series of cyanobiphenyl liquid crystal monomers with different flexible spacer chains PAOCn B(n= 0,2,6)were synthesized.The complete and uniform thickness films were prepared by in-situ UV polymerization in a liquid crystal cell.The liquid crystal properties and thermal properties of monomer and polymer were analyzed by DSC,TGA and POM,and the dielectric properties of polymer were characterized by Agilent-4294 A precise impedance analyzer.The results show that the monomer does not have liquid crystal phase,the polymer is usually nematic liquid crystal,and the polymer has good thermal stability.PAOC6 B films show the highest dielectric constant value of 3.5,while PAOC0 B films show the lowest dielectric constant value of 2.65,the value of which is related to the effective dipole moment.The type of dielectric relaxation is determined as approximate Debye relaxation by fitting the formula of dispersion curve.Secondly,the side chain liquid crystal polymer was rearranged under the stimulation of electric field,and the regulation effect of field intensity and temperature on the liquid crystal polymer in PAOC6 B thin film under DC and AC electric field respectively was explored.The DC field realizes the orientation of a large area of single-domain ordered structure,and the value of the dielectric constant increases,indicating that the dielectric constant can be increased by improving the orientation order parameters of the liquid crystal elements.The anisotropic films were reoriented by alternating AC field to break the original macroscopic ordered phase and obtain the non-anisotropic films,which reduced the dielectric constant and loss of the films.The structure of liquid crystal polymer films is controlled by electric field,which provides a new idea for improving the dielectric properties of liquid crystal polymers.