Poly(Azomethine-Ester-Si1oxane)s: Synthesis and Thermal Behaviour

Abstract

New siloxane-containing poly(azomethine-ester)s were synthesized by polycondensation reactions in solution, starting from three different azomethine mesogenic bisphenols: 4, 4'-oxo-bis(4-hydroxybenzylideneaniline), 1, 4-bis(4-hydroxybenzylideneamino)-phenylene, and 4, 4'-methylene-bis(4-hydroxybenzylideneaniline), and bis(carboxypropyl)siloxanes of various molecular weights. The reactions were performed at room temperature, activated by dicyclohexylcarbodiimide and catalysed by 4-(dimethylamino)pyridinium 4-toluenesulphonate, which is a novel synthesis method for siloxane polyesters. The polymers obtained were characterized by IR, 1 H-NMR, and UV spectroscopy, as well as by gel permeation chromatography and thermogravimetric analysis. Poly(azomethine-ester)s have good solubility in organic solvents and thermal oxidative stability. Six of the polymers obtained exhibited thermotropic liquid crystalline behaviour, evidenced by polarizing microscopy, differential scanning calorimetry, thermo-optical analysis, and wide-angle x-ray diffraction measurements. The melting and isotropization temperatures decrease with increase of the length of the siloxane spacer.