Study On Novel Phthalonitrile Resins And Wave-transparent Composites

Research on wave-transparent materials for aerospace are aimed to adapt development of modern aerospace communication and anti radar detection.Improved dielectric properties(dielectric constant is lower than 4.0,tan delta of dielectric loss is lower than 0.01)is the basic requirements for these materials.Pneumatic heating,resulting from high-speed aerocrafts,caused higher requirements for these materials with excellent thermal,mechanical and processing properties.So far,they have been divided into inorganic ceramic materials and organic resin-based composites.Compared with the former,organic polymers exhibit good mechanical properties and the advantages to form complex structures.However,applications for more high-speed aerocrafts had been limited since their lower thermostability.In order to improve the heat resistance of such materials,a series of low dielectric thermosetting resins such as bismaleimide,cyanate and polyether imide have been developed and used in wave-transparent materials in recent years.However,due to the introduction of aromatic heterocyclic structure and tight entanglement between the molecular chains,such polymers exhibited high viscosity and poor solubility(it is not conducive to preparing composite prepreg at room temperature.).At the same time,dielectric properties of these polymers also decreased significantly with the increase of temperature.From the point of view of molecular structure design,in order to obtain organic wave-transparent materials with more promoted comprehensive properties and combine the disadvantages of traditional wave-transparent resins and advantages of phthalonitrile resins,the main work was focused on development of novel crosslinked phthalonitrile resins.matrix Subsequently,we prepared organic wave transparent composite material with excellent thermostability based on these resins and used fiber glass cloth as the reinforcement.Meanwhile,novel mixed curing agents of phthalonitrile resins were developed to improve the curing activity.The main contents of this paper are as follows:(1)In order to improve the curing activity of phthalonitrile resin and shorten its curing time,two new Lewis acid/aromatic diamine mixed curing agents-ZnCl2/DDS and CuCl/DDS,were prepared in this chapter.At the same time,biphenyl-type phthalonitrile resin BP-Ph was synthesized to investigate the curing activity of the mixed curing agents.DSC results showed lower curing temperature and narrower processing window were achieved by these mixed curing agents.Rheologic data indicated gel time of the resins were shortened owing to the mixed curing agents.The mentioned mixtures were cured followed by a same procedure and the TGA suggested the condensates were thermally stable below 550 ?.(2)Design and synthesize three kinds of poly(aryl ether phthalonitrile)resins containing diazanaphthalene ketone structure:poly(aryl ether nitrile)phthalonitrile resin PPEN-Ph containing diazanaphthalene ketone structure;poly(aryl ether phthalonitrile)resin PPEBF-Ph containing trifluoromethyl and fluorene structure;and ternary copolymer PPENF-Ph combining the previous resins.Chemical structures of monomers and polymers were determined by FT-IR and 1H-NMR.Solubility tests showed that the three resins showed good solubility in Chloroform and DMF.DSC and rheological data showed that the resins had good processing fluidity and curing activity.After blended with BP-Ph,the results of TGA showed that the cured resin had no obvious mass loss below 525-550 ?.Flexural strength of glass fiber reinforced composites at room temperature was 500?700 MPa,Flexural strength and stiffness retention rate at 400 ? ranged from 55 to 80%.Dielectric constant of PPEBF-Ph and PPENF-Ph resin-based composites at 400 ? in 8-18 GHz electromagnetic wave ranged from 3.56 to 3.95 with dielectric loss tangent lower than 0.02.The dielectric properties of the composites were better than those of cyanate ester and BMI resin-based composites.(3)In order to investigate the effect of imide structure on dielectric properties of the resins,a new type of diazonaphthalene ketone polyaromatic ether phthalonitrile resin with imide structure was designed and synthesized,named PPEIF-Ph.Chemical structures of the polymers were determined by FT-IR and 1H-NMR.The resin was blended with BP-Ph and cured.The results of TGA test showed that the char yield of the cured resin was about 40%at 800 ? in air.Flexural strength and stiffness retention of glass fiber reinforced composites at 400 ? ranged from 65%to 80%.At 400 ?,the dielectric constant of composites remained at 2.91?3.86 from 8 to 18 GHz.Dielectric loss tangent was less than 0.008.The dielectric properties of composites at high temperature were better than those of other phthalonitrile-based composites in this paper.The results show that the dielectric properties of the material can be improved significantly by introducing the imide structure into the main chain of the polymer molecule with promoted thermostability.(4)In order to further improve the processing fluidity of phthalonitrile resins,branched resins THT-Ph and TT-Ph containing cyanate ester structure were designed and synthesized.Bifunctional resins BHPT-Ph and BAF-Ph containing triazine ring and hexafluorobisphenol A structure were also synthesized for comparison.Chemical structure of the resins were determined by FT-IR and 1H-NMR.Solubility tests showed that the resins were soluble in chloroform,DMF and some other solvents.The obtained resins were blended with PPENF-Ph polymer.Rheological data showed that the processing viscosity of the system can be lower than that of the PENF-Ph/BP-Ph system mentioned above by introduction of cyanate ester structure.TGA test results showed that the char yield of co-cured resin in air at 800 ?increased to about 50%.The test results of mechanical properties showed excellent bending properties and high retention rate of bending properties at high temperature.The dielectric constant of the materials in 8-18 GHz electromagnetic wave were kept between 3.67?4.03.Dielectric loss tangent was less than 0.015 at 400 ?.(5)HPN-g-PPEC-Ph resin containing phthalonitrile side chain was synthesized by nucleophilic substitution and esterification reaction.Chemical structure of the resin was determined by FT-IR and 1H-NMR.The rheological data showed that the processing viscosity of the resin decreased significantly during the heating process.After increasing the temperature to 190 ?,the viscosity could be reduced to less than 10 Pa.s,which is superior to other resins in this paper.The results of TGA showed that the thermal stability and thermo-oxidative stability of the resin were similar to those of the poly(aryl ether)phthalonitrile resin mentioned above.Relevant test results show that the flexural strength of the composites at room temperature is lower than that of the composites in other systems in this paper.The dielectric constant of the composites in 8-18 GHz electromagnetic wave was about 3.94-3.99 and the dielectric loss tangent was less than 0.01 at 400 ?.