Novel phosphorus-containing liquid crystalline copolyesters based on biphenyl mesogenic monomer (PDEBP) were synthesized by polycondensation of dimethyl biphenyl-4

4'-dicarboxylate (DBD)

diethylene glycol (DEG) and a phosphorus-containing diol

2-(6-oxido-6H-dibenz1

2oxaphosphorin-6-yl)-1

4-phenylenebis(oxy)diethanol (DOPO-HQ-HE).Chemical structure of the PDEBP was characterized by 1H-NMR spectroscopy

and the thermal and liquid crystalline behaviors of the copolyesters were investigated by thermogravimetric analysis (TGA)

differential scanning calorimetry (DSC) and hot-stage polarizing optical microscope (POM).TGA results suggested that char formation of the copolyesters was improved with the introduction of DOPO-HQ-HE without destroying the initial thermal stability of the polymer

and the residue at 700℃ in N2 (WtR700) of PDEBP7.5 (7.5 mol% of DOPO-HQ-HE in copolyester) reached 31.9 wt%

having a positive influence on flame retardance of the copolyesters.DSC tests suggested that the crystallinity of the copolyesters was destroyed by incorporating DOPO-HQ-HE into the main chain due to the bulky pendent group.The isotropic temperature (Ti) and endothermic heat (Hi) were decreased by increasing the amount of DOPO-HQ-HE

and the Ti and Hi of PDEBP7.5 reached 129℃and 1.61 J/g

respectively.POM observations showed that a typical birefringence phenomenon of nematic schlieren structure could be found in the processes of both heating and cooling

in accord with the results of DSC tests except these of PDEBP7.5

for which it was hard to find the birefringence phenomenon during heating and cooling by POM

indicating the further introduction of the phosphorus-containing diol could destroy the liquid crystalline behavior of the resulting copolyester.