Abstract
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 (T S-N =60.5℃; T N-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.
Published Version
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