Synthesis, Photoisomerization properties and Thermal Degradation Kinetics of Polyesters Containing Azomethine moiety in the main chain

A series of polyesters containing azomethine group in the main chain was synthesized by solution polycondensation of 4-[(4-hydroxy-3-methoxy phenyl)iminomethyl]phenol with various diacid chlorides. The synthesized polyesters were characterized systematically by Fourier transform infrared, UV and H-1 and C-13 NMR spectroscopy. UV analysis revealed that the synthesized polyesters have quite lower band gap than the corresponding monomer. The optical band gap values of monomer and polymer were found to be 2.80 and 2.64 respectively. Thermal properties were studied using thermo gravimetric analysis and differential scanning calorimetry. Thermogravimetric analysis indicated that the aromatic polymers had higher char yield. The self extinguishing property of the synthesized polymers was studied by the limiting oxygen index values. The aromatic polyesters had higher LOI than aliphatic polyesters. Thermal degradation kinetics have been studied using Arrhenius, Broido and Horowitz-Metzger models and calculated the activation energy (E-8) and pre-exponentional factor (A). The photoisomerization property was examined with UV spectroscopy and all these polymers showed in trans to cis isomerization 10-15 s, whereas reverse process took around 90 min in solution.