Synthesis and thermal behavior of novel poly(thiourea-amide)s derived from 1-(4-aminobenzoyl)-3- (3-aminophenyl) thiourea

The novel difunctional monomer, 1-(4-aminobenzoyl)-3-(3-aminophenyl) thiourea (ABAPT), was synthesized by the reduction of NBNPT (1-(4-nitrobenzoyl)-3-(3-nitrophenyl) thiourea). The characterization of the monomers was carried out using spectroscopic and elemental analyses. A series of novel aromatic and aromatic-aliphatic poly (thiourea-amide)s (PAMDs) were obtained through the condensation of ABAPT with various diacid chlorides (terephthaloyl, isophthaloyl, sebacoyl and adipoyl chloride). Structural elucidation of the resulting polyamides was carried out by FTIR, ¹H- and ¹³C-NMR techniques along with solvent miscibility, viscosity, molecular weight, crystallinity, non-flammable and thermal studies. The polymers bearing phenylthiourea moieties in the backbone were obtained in quantitative yield. PAMDs having inherent viscosities of 1.02-1.32 dL g⁻¹ exhibited good organosolubility in amide solvents (N,N-dimethylacetamide, dimethylformamide, dimethyl sulfoxide and N-methylpyrrolidone). X-ray diffraction studies specified crystalline behavior of new polyamides. Gel permeation chromatography measurements disclosed M_w around 34 000-65 000. The thermogravimetric analyses and limiting oxygen index measurements indicated that aromatic polyamides were stable up to 500 °C and were adequately flame retardant. Moreover, their glass transition temperatures were found to be 265-273 °C.