Highly Heat‐Resistant Phenylethynyl‐Terminated Thermoset Imide Oligomers Based on 4,4′‐(Hexafluoroisopropylidene)diphthalic Anhydride

A series of thermoset imide oligomers with a molecular weight of 1250 g/mol were prepared by a two‐step polymerization method using 4,4′‐(hexafluoroisopropylidene)diphthalic anhydride (6FDA) as the dianhydride, p ‐phenylenediamine ( p ‐PDA) and 2,2′‐bis(trifluoromethyl)benzidine (TFDB) as diamines, and 4‐phenylethynylphthalic anhydride (4‐PEPA) as the end‐capping reagent. The effect of the chemical structure of the imide oligomers on the processing properties, thermal stability, and mechanical properties was systematically investigated. The experimental results showed that the imide oligomer PI‐1 exhibited good solubility in common solvents with more than 33 wt%, and the other imide oligomers were soluble in heated N ‐methyl‐2‐pyrrolidone(NMP) with more than 33 wt%. All of the imide oligomers showed good processability, with minimum melt viscosities of less than 20 Pa s. After heat curing at 371°C for 2.5 h, the cured polyimide sheets showed T g s of 438°C–455°C, and 5% weight loss temperatures in air or nitrogen ( T d5% s) more than 530°C, and good toughness with an elongation of 7.2%–8.8%.