Syntheses And Properties Of Nitrogen-containing Heterocyclic Polybenzonitrile Resin Based On Molecular Design

As a high temperature resistant thermosetting resin,phthalonitrile resin has excellent flame retardancy,corrosion resistance,high glass transition temperature and thermal decomposition temperature,excellent thermal stability and thermomechanical properties.Many researchers have a great interest in it,and it is expected to be widely used in aerospace,microelectronics and military fields.At the same time,this type of resin also has the disadvantages of volatile catalyst,high melting point of monomer,narrow processing window and high post-curing temperature.In this paper,aiming at the shortcomings of current phthalonitrile resins,various properties of the monomers are improved by introducing nitrogen heterocycles,active hydrogens and flexible segments into the monomer structure.First,a new type of phthalonitrile monomer containing piperazine nitrogen heterocycle and active hydrogen atoms was successfully prepared（APPN）.APPN was used as a new curing agent to cure m-BDB monomer,and the catalytic performance of m-BDB resin cured with APPH was compared.TGA test shows that T_5%of APPN monomer is367°C,T_10%is 378°C,and the residual carbon rate at 1 000°C is 51.6%.It can exist stably at high temperature,which effectively solves the problem of aromatic amine curing agent volatilizing para-phthalate at high temperature.The question of the effect of dinitrile resin properties.Meanwhile,TGA showed that the T_5%of m-BDB/APPN10%was 524°C under nitrogen atmosphere and 522°C under air atmosphere.According to the calculation,its LOI is 47.3,indicating that the polymer has good flame retardancy.Furthermore,DMA showed E’to be 1 373 MPa at 400°C and T_gabove 400°C.In conclusion,the phthalonitrile resin in the presence of APPN10%has excellent thermal and thermo-oxidative stability as well as good thermomechanical properties.Secondly,using 4,4-dihydroxydiphenyl sulfide,4,4-dihydroxydiphenyl ether,2,6-dichloropyridine and 4-nitrophthalonitrile as raw materials,sulfide-containing ethers were prepared respectively.The phthalonitrile monomer with pyridine structure（PBSDP）and the phthalonitrile monomer with pyridine structure containing oxygen ether bond（PBODP）.The PBSDP monomers were cured with APPH and ODA as curing agents,respectively,and the effects of different curing agents on the thermal and thermomechanical properties of phthalonitrile resin were investigated.PBODP monomers were cured with different curing procedures and the same curing agent APPH,and the effects of curing time and curing temperature on the thermal and thermomechanical properties of phthalonitrile resin were investigated.DSC analysis showed that the melting points of PBSDP and PBODP monomers were 61°C and 69°C,respectively,the processing window was about 170°C,and the processing range was very wide.TGA analysis showed that the T_5%of PBSDP and PBODP monomers were 454°C and 460°C in nitrogen,and461°C and 465°C in air,respectively.The DMA test showed that the storage moduli of PBSDP monomer at 40°C were 3 168 MPa and 2 800 MPa,respectively,and the storage modulus of PBODP monomer at 40°C were 3 468 MPa and 2 818 MPa,respectively.Therefore,PBSDP and PBODP resins have excellent thermal and thermo-oxidative stability as well as good thermomechanical properties.