A new type of A3B3 six-arm azobenzene-containing star-shaped copolymers based on cyclotriphosphazene was prepared by stepwise nucleophilic substitution of hexachlorocyclotriphosphazene

using the sodium salt of methoxy poly(ethylene glycol) (MPEGNa) and the sodium salt of 4methoxy4′-(6-hydroxyhexyloxy)azobenzene (AZO-Na) in sequence.Structures of the resultant copolymers ［NP(MPEG550)(AZO)］3 and ［NP(MPEG1100)(AZO)］3 were characterized by Fourier transform infrared spectroscopy (FTIR)

proton nuclear magnetic resonance spectroscopy (1H-NMR) and gel permeation chromatography (GPC).Thermal properties of both sixarm azobenzene containing copolymers were investigated by differential scanning calorimetry (DSC) and polarizing optical microscopy (POM).DSC result showed that ［NP(MPEG550)(AZO)］3 showed reversible thermotropic liquid crystalline (LC) behavior (TS-N=60.5℃; TN-I=104.7℃

by the second heating DSC curve) and was an enantiotropic LC polymer.Nematic droplets texture was observed by POM

but smectictonematic translation was not clear.This might be related to the complex LC phase transition process with the unique molecular structure of ［NP(MPEG550)(AZO)］3.It was not observed the thermotropic LC transition of ［NP(MPEG1100)(AZO)］3 by DSC and POM.This might be the result of the difficulty of crystallization of azobenzene segment linked to the long and flexible PEG chains with big volume fraction in the ［NP(MPEG1100)(AZO)］3.Thermotropic liquid crystalline behavior of such A3B3 polymers was mainly relevant to the chemical property and volume fraction of different arms.