Synthesis And Characterization Of Novel Asymmetric Dimers Containing Mandelic Acid

Two series of liquid crystal(LC) dimers containing chiral mandelic acid as the center of asymmetric dimers have been synthesized in this dissertation.The effects of molecular rigidity and terminal polarities on the properties were studied.In this dissertation,eight intermediate compounds have been successfully synthesized,termed as 4-butoxybenzoic acid(QBA),4-((4-butoxybenzoyl)oxy)benzoic acid(QBBA),2-((4-butoxybenzoyl)oxy)-2-phenylacetic acid(QBMA),2-((4-((4-butoxybenzoyl)oxy)benzoyl)oxy)-2-phenylacetic acid(QBBMA),4-hydroxy phenylbenzoate(B2),4-hydroxyphenyl4-(trifluoromethyl)benzoate(FB2),4’-hydroxy-[1.1’-biphenyl]-4-yl4-(trifluoromethyl)benzoate(FB3)and 2-hydroxy propyl4’-((4-(trifluoromethyl)benzoyl)oxy)-[1,1’-biphenyl]-4-carboxylate(PFB3).A series of asymmetric dimers containing cryano,termed as CN series,have been successfully synthesized with QBMA and phenol(B),4-hydroxybenzonitrile(BCN),4’-hydroxy-[1,1’-biphenyl]-4-carbonitrile(BBCN)and QBBMA and BBCN,respectively.They are 2-oxo-2-phenoxy-l-phenylethyl-4-butoxybenzoate(QBMA-B),2-(4-cyanophenoxy)-2-oxo-1-phenylethy14-butoxybenzoate(QBMA-BCN),2-((4’cyano-[1,1’-biphenyl]-4-yl)oxy)-2-oxo-1-phenylethyl4-butoxybenzoate(QBMABBCN)and 4-((2-((4’-cyano-[1,1’-biphenyl]-4-yl)oxy)-2-oxo-1-phenylethoxy)carbonyl)pheny 14-butoxybenzoate(QBBMA-BBCN).A series of asymmetric dimers containing trifluoromethyl,termed as F series,have been successfully synthesized with QBMA and B2,FB2,FB3 and PFB3,respectively.They are 2-(4-(benzoyloxy)phenoxy)-2-oxo-1-phenylethyl4-butoxy benzoate(QBMA-B2),4-(2-((4-butoxybenzoyl)oxy)-2-phenylacetoxy)phenyl4(trifluoromethyl)benzoate(QBMA-FB2),4’-(2-((4-butoxybenzoyl)oxy)-2-phenyl acetoxy)-[1,1’-biphenyl]-4-y14-(trifluoromethyl)benzoate(QBMA-FB3),2-(2-((4butoxybenzoyloxy)-2-phenylacetoxy)propyl4,4’-((4-(trifluoromethyl)benzoyl)oxy-[1,1’-biphenyl]-4-carboxylate(QBMA-PFB3).The chemical structures and LC properties of the intermediates and two series of dimers were investigated by FTIR,differential scanning calorimetry(DSC),polarised optical microscopy(POM)and XRD.The molecular structures of all the intermediates and dimers are all consistent with those of the design.QBMA,QBBMA and B2 are not LCs.QBMA-B is not a LC dimer.Others all displayed the properties of the LCs.QBMA-BCN and QBMA-PFB3 are thermotropic monotropic nematic LCs.QBMA-BBCN,QBMA-B2 and QBMA-FB2 are thermotropic enantiotropic nematic LCs.QBBMA-BBCN is a thermotropic enantiotropic cholesteric LC.QBMA-FB3 is a thermotropic enantiotropic smectic LC.The results of the CN series indicated that cyano group and benzene ring introduced into the dimers could stabilize the mesophase.The melting temperatures of four asymmetric LC dimers increased first and then decreased.This may be attributed to the fact that the melting temperatures are not only affected by molecular weight,polarity and rigidity,but also by the molecular shape.The introduction of mandelic acid could induce a cholesteric phase,but the formation of the cholesteric phase is also related to the molecular conformation.The results of the F series revealed that the melting temperatures of four asymmetric LC dimers increased first and then decreased under the influence of molecular weight,polarity,rigidity and molecular shape.The F3C polar group not only affects the thermal properties of the dimer but also enhances the intermolecular force,which tends to form a smectic phase.