Pyridine-thiourea based high performance polymers: Synthesis and characterization

Abstract

A novel diamine monomer, pyridine-2, 6-bis((4-aminophenyl)thioureido)carbonyl (PATC) was synthesized efficiently and polymerized with various aromatic dianhydrides. Consequently, poly(pyridine thiourea-imide)s (PPTIs) with good thermal properties and flame retardancy were fabricated. The structures of PATC and PPTIs were characterized by FTIR, ¹H-NMR, ¹³C-NMR spectroscopy along with elemental analysis, crystallinity, organosolubility, inherent viscosity and gel permeation chromatographic measurements. PPTIs containing C=S, CONH and meta substituted pyridine moieties in the polymer backbone showed amorphous nature and were readily soluble in highly polar organic solvents and even in less polar solvents such as tetrahydrofuran (THF). Polymers had inherent viscosities in the range of 0.91–1.16 dL/g and molecular weight was found between 68000–77000 g/mol. The electrical properties of the PPTIs were estimated in terms of dielectric constant over a range of frequencies. Their thermal stability was determined by 10% weight loss temperature found in the range of 519–563 °C under inert atmosphere. The glass transition temperature of the polyimides varied between 247 °C and 267 °C. The flame retardant properties of PPTIs were investigated in terms of limiting oxygen index (LOI) which was found in the range of 38.26–39.95. Introduction of thiourea in the polymer backbone is an effective way to improve the thermal stability and flame retardancy. Thus PATC can be considered as an excellent candidate for the synthesis of high performance polymers.