Highly heat-resistant and soluble phenylethynyl-terminated thermoset imide oligomers based on pyromellitic dianhydride

Abstract

A series of thermoset imide oligomers have been prepared by the thermal polycondensation of pyromellitic dianhydride (PMDA) with two different aromatic diamines, bis(4‐amino‐2‐trifluoromethylphenyl)ether (TFODA) and 2,2'-bis(trifluoromethyl)benzidine (TFDB) in the presence of 4-phenylethynylphthalic anhydride (4-PEPA) as an end-capping reagent. The effects of different diamine ratios and different molecular weights on the solubility and melt viscosity of imide oligomers, as well as on the thermal and mechanical properties of cured polyimide sheets were investigated. The experimental results showed that the imide oligomers PI-1, PI-2, PI-3, and PI-4 exhibited good solubility (≥33 wt%) in common solvents. Among them, PI-2 showed the best processing properties with a minimum melt viscosity of 4.8 Pa·s. After thermally curing at 371 °C for 2.5 h, the cured polyimide sheets showed glass transition temperatures (T_gs) of 413-472 °C, 5% weight loss temperatures (T_d5%s) of 560-578 °C in both air and N₂ atmosphere, and good toughness with elongation of 8.6-19.1%.