Novel flame retardant poly(thiourea-sulfone-imide)s for high temperature applications: synthesis and characterization

The synthesis and polymerization of a novel diamine monomer, 1,1-(sulfonylbis (4,1-phenylene)) bis (thiourea) (SPT), with various aromatic dianhydrides were carried out. In addition, the fabrication of poly(thiourea-sulfone-imide)s (PTSIs) with noble thermal properties and flame retardancy was conducted. The structures of SPT and polymers were characterized by FT-IR, ^1H NMR, and ^{13}C NMR spectroscopy along with elemental analysis. Crystallinity, organosolubility, inherent viscosity, and gel permeation chromatographic measurements were taken as well. The amorphous nature was exhibited by PTSIs containing C=S and --SO_2- moieties in the backbone that were readily soluble in highly polar organic solvents. The inherent viscosities of PTSIs were 0.89--1.13 dL g^{-1} and molecular weights were 87,000--96,550 g mol^{-1}, respectively. Their thermal stability was studied in terms of temperature at 10% weight loss, which ranged between 478 and 526 °C under inert atmosphere. Polyimides had a glass transition temperature around 253--268 °C depending on the dianhydrides used. The flame retardant properties of PTSIs were studied in terms of limiting oxygen index values and were measured in the range of 50--56.