Study On Synthesis Of Bisphenol F Phthalonitrile Resin And Properties Of Its Composites

The polyphthalonitrile resin is a high-performance polymer formed by the addition polymerization reaction of a phthalonitrile resin monomer through a cyano group.The cyano group generates an aromatic heterocyclic three-dimensional crosslinked network structure mainly composed of a phthalocyanine ring and a triazine ring under an active hydrogen source.The aromatic heterocyclic ring itself belongs to a conjugated structure and has outstanding temperature resistance properties,giving polyphthalonitrile resin excellent thermal stability,thermal oxygen stability,flame retardancy,chemical resistance and low water absorption,and can be done It is a new type of base resin for heat-resisting and ablative composites.At present,phthalonitrile resins also have the following problems:①Many PN monomers have high melting point,narrow processing window,low curing reaction rate,and require higher curing temperature and longer curing time,even though they pass the molecular structure.The design solved some problems,but increased the difficulty and cost of the synthesis.②The current research mainly focused on the structure and properties of phthalodinitrile resins,the study of phthalonitrile resin-based composite materials,especially ablation resistance,is still less.Based on the molecular structure design,the subject successfully synthesized bisphenol F-phthalonitrile(BFPH)monomer through one-step simple nucleophilic substitution reaction.It has the advantages of simple operation,easy control,etc.,It was characterized by infrared spectroscopy(FT-IR),elemental analyzer and mass spectrometry(MS).The use of bis4-(3-aminophenoxy)phenyl sulfone(m-BAPS)having excellent thermal stability as a curing agent initiates polymerization of bisphenol F type resin monomers.Differential scanning calorimetry(DSC)analysis showed that the BFPH had a melting point of 52 °C and a curing peak temperature of 253 °C with a wide processing window.The rheometer test showed that the complete flow temperature of BFPH was 120 ℃and the gelation time was 31.1 min at 180°C.FT-IR,TGA,universal material testing machine and dynamic thermomechanical analyzer(DMA)were used to study the properties of the cured BFPH at different post-cure temperatures.The results showed that:With the increase of post-cure temperature,BFPH curing more and more complete,its cured glass transition temperature(Tg),thermal stability,mechanical properties have significantly improved.The flame retardancy test showed that the limiting oxygen index of the cured BFPH was greater than 45%,the highest vertical combustion rating was VO,and the smoke density was less than 20.Scanning electron microscopy(SEM)shows that the cured BFPH has a smooth section and is brittle.BFPH/2.5D carbon fiber and phenolic resin/2.5D carbon fiber ablative composites were prepared by the solution method.The mass fraction of the resin in the two composites was about 35%,the density was between 1.4 to 1.45g/cm3,and the porosity was lower 10%.The mechanical properties test shows that the BFPH resin matrix composites are superior to the phenolic resin matrix composites in terms of mechanical properties,especially the interlaminar shear strength(ILSS)is 107%higher than that of the phenolic resin matrix composites.The specific heat capacity,thermal conductivity,mass ablation rate and line ablation rate of BFPH resin-based composites were lower than those of phenolic resin-based composites,indicating that BFPH resin-based composites have better ablation resistance.The BFPH resin-based composite material was subjected to carbonization test.The maximum carbonization temperature was 950 °C,and the residual carbon ratio of the resin was about 62%.