Preparation And Properties Of Polyphthalonitrile Resin And Its Composites

Polyphthalonitrile resin is a kind of thermosetting resin with high performance and high temperature resistance. It is prepared through phthalonitrile monomer with curing agent under addition polymerization reaction. With excellent thermal stability, thermal oxidative stability, flame resistance, moisture resistance and good mechanical properties, the resin is expected to be widely used in aerospace, shipbuilding, electronics packaging and other fields. However, due to the high melting point of phthalonitrile monomer, it is difficult to process. Moreover, polyphthalonitrile resin has inherent brittleness because of its generation from crosslinked benzene rings which have rigid structure. Consequently, during these years, domestic and foreign researches have been committed to reduce melting point of phthalonitrile monomer, to improve the processing performance, and to change the structure of the molecular chain so as to improve the toughness of the polyphthalonitrile resin.Based on molecular design, the phosphazene was introduced into the phthalonitrile monomer and polyphthalonitrile resin based on phosphazene was synthesized for the first time. Then the structure of the phthalonitrile monomer is characterized through Infrared Spectrum and Nuclear Magnetic Resonance Hydrogen Spectrum. Afterwards, 4-hydroxyphenoxy phthalonitrile with autocatalytic properties is employed as curing agent to initiate monomers polymerization and form polymer. Differential scanning calorimetric(DSC) analysis shows that the phthalonitrile monomer has lower melting point and a larger processing temperature window. Thermogravimetric analyzer(TGA) shows that initial decomposition temperature(Td5%) of the phthalonitrile resin is higher than 500℃. Dynamic mechanical analysis(DMA) shows that the glass transition temperature of the phthalonitrile resin is higher than 380℃. After a long period of thermal oxidative property analysis, the weight of the resin loses only 2.06%. Besides, the apparent activation energy of the resin was calculated through Kissinger non-kinetic equations.Since the curing agent often volatilizes during heat curing, which will reduce the polymerization rate and influence the processing properties of the resin, a new kind of naphthyl-based autocatalytic phthalonitrile monomer was prepared. The monomer can polymerize automatically without curing agent. The thermal properties and thermal stability of the monomer was analyzed through DSC and TGA. Even at 800℃, the char yield of the polymer is still high, indicating that it has good heat resistance. By extending curing time, the polymerization reaction is further carried out and the degree of crosslink gradually increases and that improves the thermal oxidative stability of the polymer.Besides changing the molecular structure, micro-nano-particles are also used to improve the toughness of the resin. A new composite material through adding boron nitride with high performance into phthalonitrile resin was prepared. Analysis indicates that after the addition of boron nitride, the performance of the resin, especially the thermal conductivity remarkably increases. In addition, for the first time the boron nitride is modified with nanodiamond and the interfacial interaction between boron nitride and the matrix resin is improved. Adding the modified boron nitride, the thermal conductivity of phthalonitrile resin is much better than before.