A series of main chain liquid crystalline copolyesters with X-shaped two-dimensional mesogenic units and crown ether cycles of cis-4

4′-bis(4-hydroxyphenylazo) dibenzo-18-crown-6 was synthesized via solution cocondensation polymerizations from 4

4′-(α

ω-octanedioyloxy) dibenzoyl dichloride(M1)

2

5-bis(p-decyloxyphenylbenzoyloxy)hydroquinone (M2) and cis-4

4′-bis(4-hydroxyphenylazo) dibenzo-18-crown-6 (M3) as the monomers.Monomer M1 was synthesized by esterification and substitution reactions of p-hydroxybenzoic acid and octanedioyl chloride.Monomer M2 was synthesized by esterfication and reduction reactions of 2

5-dihydroxybenzoquinone and p-decyloxyphenylbenzoyl chloride.Monomer M3 was synthesized by diazotization and coupling reactions of cis-diaminodibenzo-18-crown-6 and phenol.The molecular weights of copolyesters were not high

and the ［η］ of the copolyesters was in the range the of 0.39～0.30 dL/g.The monomer structures were identified by using elementary analysis

IR

UV

1H-NMR and MS etc.All the copolyester samples were yellowish powders and insoluble at room temperature in THF and CHCl3 except the sample CP9. The properties of copolyesters were investigated by using GPC

［η］

DSC

TG

WAXD and POM.It was found that all the copolyesters went into liquid crystal phase when they were heated over their melting temperature (Tm).CP2～CP8 can exhibit both smectic and nematic phases

and the typical liquid crystal textures of smectic and nematic phases can be observed. CP1 and CP9 only have nematic phase. The melting temperature and isotropic temperature (Ti) of all copolyesters increased regularly with increasing the cis-4

4′-bis(4-hydroxyphenylazo) dibenzo-18-crown-6 unit content in the copolyesters for the reason that the flexibility of —OCH2OCH2— chains in comonomer M3 rendered the copolymer to build up regular structure easily and increase its degree of ordered arrangement. The temperatures of 5% weight loss

(Td) in TG experiments were in the range of 318.5～366.3℃ and increased with an increase of the content of T-shaped mesogenic units in the copolyesters. The reason is that the T-shaped two-dimensional mesogenic unit has a very rigid structure and high thermal stability. Increasing the content of T-shaped two-dimensional mesogenic units will improve the thermal stability of the copolyesters. The WAXD studies illustrated that the copolyesters were liquid crystalline with a nematic phase. A dispersive peak at 2θ near 20° appeared in their WAXD patterns

which is a typical character for quenched nematic liquid crystal copolyesters.