LIQUID-CRYSTALLINE POLYETHERS BASED ON CONFORMATIONAL ISOMERISM .24. SYNTHESIS AND CHARACTERIZATION OF CYCLIC LIQUID-CRYSTALLINE OLIGOMERS BASED ON 1-(4-HYDROXY-4'-BIPHENYLYL)-2-(4-HYDROXYPHENYL)BUTANE AND 1,10-DIBROMODECANE

The synthesis of cyclic monomer, dimer, trimer, tetramer, and pentamer based on 1-(4-hydroxy-4'-biphenylyl)-2-(4-hydroxyphenyl)butane (TPB) and 1,10-dibromodecane and their characterization by 300-MHz 1-D H-1-NMR and 2-D H-1-NMR COSY and NOESY spectroscopies, differential scanning calorimetry, and optical polarized microscopy are presented. Their phase behavior was compared with that of the linear high molecular weight polymer based on TPB and 1,10-dibromodecane. The cyclic monomer is liquid. The larger cyclic compounds exhibit a nematic mesophase and a very slow crystallization tendency. Their melting temperature shows an odd-even dependence on ring size, while their isotropization transition temperature shows a continuous increase versus ring size. The cyclic tetramer and pentamer exhibit higher isotropization transition temperatures but lower enthalpy and entropy changes than the corresponding linear high molecular weight polymer. An explanation for this behavior is provided.