Aromatic polyesters with photosensitive side chains: Synthesis, characterization and properties

Abstract

New aromatic polyesters with photosensitive groups in their pendant chains were prepared from a diphenol carrying as substituent a cinnamoyl group extended with a flexible oxyethyleneoxy spacer and different aromatic dicarboxylic acids via direct polyesterification reaction in the presence of the tosyl chloride/pyridine/dimethylformamide system as condensing agent. The resulting polyesters were characterized using Fourier-transform IR, proton and carbon nuclear magnetic resonance and ultraviolet spectroscopy, differential scanning calorimetry, thermogravimetric analysis, wide-angle X-ray diffracto­metry, gel permeation chromatography, viscosity measurement and solubility tests. These polyarylates had moderate inherent viscosities ranging from 0.37 to 0.54 dL g-1, good solubility in polar aprotic solvents, and afforded trans­parent, colorless and apparently tough films on casting from their solutions. Their glass-transition temperatures ranged from 136 to 154 °C. None of them showed significant decomposition below 320 °C and all retained 38–47 % of their weight at 700 °C in a nitrogen atmosphere. The presence of cinnamoyl chromophore endowed these polymers with the ability to interact with ultra­violet light, which resulted in photodimerization between the cinnamoyl side groups upon irradiation at l = 365 nm and cross-linking of the polymers chains without the necessity of photo-initiators or photosensitizers. Consequently, the polymer films became insoluble in organic solvents.