Modification on phthalonitrile containing benzoxazine with cyaniding diamine-type benzoxazine: Curing reaction and properties of their glass fiber-reinforced composites

Phthalonitrile resin is a kind of high-performance thermosetting resins. Decreasing the curing temperature and accelerating the curing reaction rate have become the focus of research on phthalonitrile modification. Based on the reactivity, thermal and mechanical properties of diamine-type benzoxazine, a monocyano-functionalized diamine-type benzoxazine (MD-cn) was synthesized and applied to modify bisphthalonitrile resin containing bisphenol-type benzoxazine/nitrile phenylenediamine (BA-ph/BAB). Curing reaction properties and curing mechanism of BA-ph/BAB/MD-cn were studied by gelation time, DSC, DRA and in-situ IR. Results showed that MD-cn could significantly boost the curing reaction rate and reduce its curing temperature of BA-ph/BAB. Meanwhile, glass fiber reinforced composites (BA-ph/BAB/MD-cn/GF) was prepared and their properties were studied. Results showed that MD-cn improved the crosslinking density and curing degree of BA-ph/BAB could make the BA-ph/BAB/MD-cn resin matrix possess higher stiffness. Therefore, BA-ph/BAB/MD-cn/GF composites exhibited higher flexural strength (494 MPa, increased 40%) and flexural modulus (26 GPa, increased 13%) as well as good dimensional stability. Compatibility between MD-cn and BA-ph/BAB was investigated by DMA and SEM. Moreover, with the increase of MD-cn content, the good thermal stabilities (T5%>404.5 °C, Yc, 800 °C>66%) of cured BA-ph/BAB/MD-cn were obtained. Besides, interfacial adhesion properties of BA-ph/BAB/MD-cn/GF composite laminates were also studied.