Enhanced thermal properties of phthalonitrile networks by cooperating phenyl-s-triazine moieties in backbones

The development of phthalonitrile resins is of particular interest for aerospace applications because of their excellent heat resistance. Here, heteroaromatic phenyl-s-triazine moieties have been introduced into the architecture of the phthalonitrile resin as thermally stable segments via a two-step, one-pot reaction. Bis(4-[4-aminophenoxy]phenyl)sulfone was selected to promote the curing reaction, and the gelation time could be readily controlled by the diamine concentration and the curing temperature as evidenced by rheometric measurements. The curing procedure was optimized to give high cross-linking density networks. The resulting networks exhibit high glass transition temperatures at around 400 °C, outstanding thermo-oxidative stability with weight retention of 95% ranging from 539 °C to 552 °C, suggesting an improvement of the thermal properties imposed by phenyl-s-triazine units. Additionally, the CF laminate of the resin possesses high flexural strength of 1722 MPa and interlaminar shear strength of 71 MPa at ambient temperature, and these values retain 255 MPa and 36 MPa at 450 °C, respectively.