Preparation of new phenylethynyl terminated imide oligomers from pyromellitic dianhydride

Phenylethenyl end-capped imide oligomers based on pyromellitic dianhydride (PMDA), 2, 5-bis(4-aminophenoxy)-biphenyl (p-TPEQ) and 4-phenylethynylphthalic anhydride (PEPA) were prepared. The thermal properties and melt viscosity of oligomers were investigated by differential scanning calorimetry, thermogravimetric analysis and rheological studies, respectively. The oligomers bearing pendant phenyl groups exhibited much lower melt viscosities than PETI-5, and provided broader processing window. Thermal curing processing was monitored by Fourier transform infrared spectrometry, crosslink reaction of phenylethynyl end group completed at 370°C in 20 min. Glass transition temperatures of cured oligomers determined by DMA were about 273 to 330°C, which was much higher than PETI-5. In addition, these cured imide oligomers exhibited excellent tensile properties with strength about 100 MPa and modulus more than 2 GPa. Finally, the films cured by oligo-6 were aged at 177°C for different times and they still exhibited excellent thermo-oxidative stabilities after aging. It is concluded that using inexpensive PMDA not only lowers the cost, but also increases the glass transition temperature after curing. The excellent properties of these phenylethynyl end-capped imide oligomers demonstrate a promising potential for future aerospace applications.