Facile synthesis and properties of a new generation of soluble and thermally stable polyimides

A new diamine, 1,4-phenylene bis((E)-1-(4-chloro-3-aminobenzylidene) thiourea) (PCABT), containing phenylthiourea and azomethine groups was prepared from the reduction of dinitro compound, 1,4-phenylene bis((E)-1-(4-chloro-3-nitrobenzylidene)thiourea), PCNBT. The structures of resulting monomers were characterized by elemental analysis, FTIR, 1H and 13C NMR techniques. Afterwards, this diamine was reacted with various aromatic dianhydrides (ODPA, BTDA and 6FDA) in glacial acetic acid to afford poly(phenylthiourea azomethine imide)s (PPTAIs) with ηinh of 1.59-1.66 dL/g, depending on the dianhydride used. The ensuing PPTAIs exhibited ample solubility in organic solvents (DMAc, DMF, DMSO and NMP) and were obtained in quantitative yields. Also, all polyimides were amorphous according to wide-angle X-ray determination. GPC measurements of polymers revealed Mw around 69,000-72,000. Moreover, thermogravimetric analyses indicated that PPTAIs were fairly stable up to 550 °C, and 10% weight loss temperatures were recorded in the range of 563-578 °C (N2 atmosphere). Ultimately, these polyimides own high glass transition temperatures about 281-285 °C.