Novel catechol-derived phosphorus-based precursors for coating applications

Abstract

Depletion of the petroleum resources and poor flame-retardant properties of the epoxy resins drive researchers to develop an epoxy resin with good heat stability from bio-resources. In the current research work, we have reported the synthesis of a novel crosslinking agent for epoxy from the catechol as a bio-resource which can be further modified to form epoxy resin as well. The synthesis of the flame-retardant epoxy resin (TOMPP) was performed in two separate steps which include the reaction of the catechol with phosphoryl chloride followed by the reaction of the remaining hydroxyl groups with the epichlorohydrin. The structures of the synthesized products were confirmed using Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy and hydroxyl and epoxy values. The thermogravimetric analysis and differential scanning calorimetry were performed to analyse the thermal stability of the cured films which showed thermal degradation temperatures of both TOMPP and THPP formulations were decreased as the concentration of the TOMPP and THPP increased, while glass transition temperature (Tg) values increased. The char yield value of the THPP formulations was increased with increasing concentration of the intermediate, but for TOMPP it decreased. 40% THPP showed the least current density in electrochemical impedance spectroscopy suggesting the good corrosion resistance property. Mechanical properties were found to be similar for both THPP and TOMPP formulations. Flame retardancy was checked by LOI and UL-94 tests which revealed 40% THPP formulation had the maximum LOI as 28 and self-extinguishing behaviour.