Synthesis and properties of soluble polyimides containing tert-butyl, ether linkages, and triphenylmethane units

Abstract

A molecular theory design was carried out to synthesize a diamine monomer 1-(4-tert-butylphenyl)-1,1-bis[4-(4-aminophenoxy)] phenylethane containing tert-butyl, ether linkage, and triphenylmethane units. Then it was polymerized with several commercial aromatic dianhydrides, including diphenyl hexafluoroisopropylidene tetraic acid dianhydride (6FDA), diphenyl ether tetracarboxylic dianhydride (ODPA), biphenyltetracarboxylic dianhydride (BPDA), and benzophenone tetraacid dianhydride (BTDA), via the conventional two-step method to afford a series of aromatic polyimides (PIs). The structure and properties of the polymer were characterized by Fourier transform infrared (FTIR) spectroscopy, solubility test, thermogravimetric analysis, differential scanning calorimetry, ultraviolet–visible spectroscopy, and tensile tests. The results showed that there were characteristic peaks of PI around 1776, 1720, and 1378 cm−1 in the FTIR spectra; 6FDA-, ODPA-, and BPDA-based PI are easily soluble in N-methylpyrrolidone (NMP), concentrated sulfuric acid, N,N-dimethylacetamide (DMAc), pyridine, Tetrahydrofuran (THF), Trichloromethane (CHCl3), and other common organic solvents showing excellent solubility. In a nitrogen atmosphere, the glass transition temperature of the PI films are between 246°C and 275°C, the temperature of 5% weight loss is above 501°C, and the residual mass fraction at 750°C is 53–61%. The mechanical properties range from 67.2 MPa to 88.6 MPa. In addition to the BTDA-based PI film, the other three types of PI have good transparency. The simultaneous introduction of tert-butyl, ether linkages, and triphenylmethane units has a synergistic effect, which greatly improves the solubility of PI and maintains good thermal stability, mechanical properties, and optical properties of PI at the same time.