Synthesis of liquid crystals of non-chiral β-methylbutyl polybiphenyl isothiocyanate and high-frequency dielectric properties
Six new isothiocyanato-non-chiral β-methylbutyl polybiphenyl liquid crystal compounds A1～A6 are designed and synthesized by various synthetic methods,such as Appel reaction,Grignard reaction,Suzuki coupling reaction,etc.,using achiral DL-(±)-2-methyl-1-butanol and bromobenzene as raw materials,and the molecular structures,phases,and microwave dielectric properties of these compounds have been tested and analyzed.The results show that the melting points of the triphenyl liquid crystal compounds A1～A3 gradually decrease with the increase of the number of fluorine atoms,and the lowest melting point reaches 37℃,and the width of its nematic phase temperature reaches 71℃.When the substituents of fluorine atoms are in the same position and the same number,the melting point of the compounds with β-methylbutyl is lower than that of the compounds with n-butyl group.However,when the substituents of the tetrabiphenyl benzene ring side position are changed,the melting point of the—F-substituted compounds A4 is the lowest,followed by that of the—CH3 substituent A6,and—Cl substituent A5 has the highest melting point,and all three of them have a nematic phase temperature range of more than 120℃.In the microwave band 9～30 GHz,compounds A2～A6 show good dielectric properties with dielectric anisotropy greater than 0.903 and vertical dielectric loss values between 0.003 3～0.010 7,among which the vertical dielectric loss of compound A6 is as low as 0.003 8 with a quality factor of 66.12 at 19 GHz.The different substituents contribute differently to the reduction of the maximum(vertical)dielectric loss:—CH3＞—Cl＞—F,and the magnitude of different substituents to the improvement of the dielectric anisotropy(Δεr)value is—F＞—Cl＞—CH3.
liquid crystals for microwavedielectric lossβ-methylbutyl polybiphenylsfluorine substitutionsynthesis
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