Solubility, electrochemical behavior and thermal stability of polyimides synthesized from 1,3,5-triazine-based diamine

Abstract

In order to acquire a series of solution-processable polyimides, synthesis of triazine-based diamine monomers 6-phenyl-1,3,5-triazine-2,4-diamine(PTDA) and 6-(4-fluorophenyl)-2,4-diamino-1,3,5-triazine(FPDT) was reported. On the basis of the synthesized diamines and a commercial available diamine, 6-methyl-1,3,5-triazine-2,4-diamine(MTDA), a series of polyimides(PIs), containing benzene or fluorobenzene as pendent group and triazine ring in the skeleton were synthesized. The two-step route constituted of ring-opening polymerization to form poly(amic acid)s (PAAs) and further thermal imidization to obtain the aiming PIs. Fourier transform infrared (FT-IR) was used for chemical structural characterization of the resulting PIs. The crystalline morphology of the PIs powder were explored by X-ray diffraction(XRD) patterns, and the minimum 2θ peak of PI-a split into to two peaks, which can be explained by result of coefficient between the torsion and 1,4 VDW energy with the help of calculation of Chem 3D Pro. Compared with common polyimides, most of the resulting PIs has excellent solubility in polar aprotic solvents, such as NMP, DMSO, DMAc and DMF. Meanwhile, after modification of diamine by the benzene or fluorobenzene as pendent group, PI-b (synthesized from PTDA and PMDA) and PI-c (synthesized from FPDT and PMDA) exhibited more excellent thermal stability compared with PI-a (synthesized from MTDA and PMDA) without sacrificing apparent solubility. Cyclic voltammetry(CV) method was used to investigate the electrochemical behavior of the resulting PIs, showing that electrochemical gap of PI-b and PI-c were 1.360 and 1.217 eV, respectively. By means of the thermogravimetric analysis(TGA) and the differential scanning calorimeter(DSC), the relationship between annealing temperature and thermal behavior of the resulting PI was discussed, revealed that 300–340 °C annealing render the PI best thermal behavior. Based on the performances, the resulting polyimides reveal their broad application prospect in polymer semiconductors.