Novel copolyhydrazides and copolyoxadiazoles based on 1,4-phenyl linkage and 1,3,4-thiadiazole moiety in the polymer Main chain to induce glass transition and to improve the thermal stability, solubility, and antimicrobial activity

Abstract

Polyhydrazides (PHs) and polyoxadiazoles (PODs) have broad potential applications, but PHs are generally not high-temperature resistant and PODs are commonly insoluble in organic solvents, degrade before melting, and do not show glass-transition temperature (Tg). These limitations make their processing quite difficult. To overcome these shortcomings, novel copolyhydrazides (CPHs) and copolyoxadiazoles (CPODs) based on 1,4-phenyl linkage and 1,3,4-thiadiazole moiety in the main chain have been synthesized. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) were performed to assess the polymers thermal behavior. Also, the crystalline structure and surface morphology were examined using X-ray diffraction (XRD) and scanning electron microscopy (SEM). In addition, their solubility, viscosity, UV-visible absorption, antimicrobial characteristics were studied. Most of the new CPHs and CPODs showed high thermal stability and good solubility in polar aprotic solvents. Moreover, the CPODs melted and showed Tg and fortunately their Tg values are still high (>227 °C), so they are suitable for use under extreme conditions. It seems that incorporating 1,4-phenyl linkage and 1,3,4-thiadiazole moiety into the polymer main chain enhanced the solubility and suppressed the crystallinity, while kept the thermal stability. Furthermore, the CPODs gave large antibacterial and antifungal activities, confirming the possibility to be used in medicinal fields.