Synthesis and characterization of novel wholly aromatic azopolyamide-hydrazides

Abstract

The influence of controlled structural variations upon the physical, thermal and mechanical properties of a series of novel wholly aromatic azopolyamide-hydrazides has been investigated. The polymers were prepared by a low temperature solution polycondensation reaction of p-aminosalicylic acid hydrazide (PASH) and an equimolar amount of either 4,4′-azodibenzoyl chloride (4,4′ADBC), 3,3′-azodibenzoyl chloride (3,3′ADBC), or their appropriate combinations in anhydrous N, N-dimethyl acetamide (DMAc) as solvent at −10 °C. The content of para-/ meta-phenylene units was varied within this series between 50/50 and 100/0. Polymer structures were characterized by elemental analysis and infrared spectrometry. Polymer properties were evaluated by intrinsic viscosity, solubility, moisture regain, thermal and thermo-oxidative stability, mechanical properties and X-ray diffraction. The results obtained during the preparation of these polymers, their subsequent structural characterization and their property evaluations are discussed. All the polymers have the same structural formula except the way of linking phenylene units inside the polymer chain. The polymers intrinsic viscosities were ranged from 1.5 to 4.3 dl g −1 in DMAc/3% LiCl at 25 ± 0.1 °C and increased with the increase of para-phenylene units content. The polymers are found to be partially soluble in polar aprotic solvents like DMAc, dimethyl formamide [DMF], and N-methyl pyrrolidone (NMP) at room temperature. Their solubilities in these solvents were found to be enhanced remarkably by adding LiCl and their solutions could be cast into flexible films. All the polymers dissolved freely in concentrated sulphuric acid but with degradation. The polymers having para-linkages in this series are less soluble than the polymers having meta-linkages. The prepared polymers exhibit a great affinity to water sorption. The hydrophilic character increases as a function of meta-phenylene rings content incorporated into the polymer. Thermogravimetric measurements indicated that the perfectly p-oriented type of polymer has better thermal and thermo-oxidative stabilities relative to that of the other polymers. Mechanical properties of the polymers films are improved markedly with introduction of para-phenylene nuclei into the polymers. All these polymers were found to be amorphous as confirmed by X-ray diffraction.