Preparation And Properties Of Polyphthalonitrile Resin And Its Copolymers

Polyphthalonitrile is a thermoset polymerized by phthalonitrile with curing agents like aromatic amines.Thanks to the excellent thermal stability,outstanding mechanical properties even at elevated temperature,low moisture resistance and great flame retardance,polyphthalonitrile,as a rising high-performance resin,have drawn great attention for its superiority to other conventional high performance polymers such as polyimides,polybenzoxazine,and polyetherether-ketone.Besides,phthalonitrile monomers could be readily processed into highly crosslinked void-free thermosets,rather than generate by-products during polymerization because of its addition polymerization mechanism.Based on those merits,polyphthalonitrile is promised to be widely used for aerospace,marine,and microelectronic areas.In consideration of the status that most of the efforts in study area about polyphthalonitrile were concentrated on improving the processability while neglect to enhance its outstanding thermal stability and stiffness to some extent,In this study,a new kind of pyridine-containing phthalonitrile monomer,namely 2,6-bis[4-(3,4-dicyanophenoxy)benzoyl]pyridine(BCBP),which introduced this quite thermally stable structure into its backbone.Then,the phthalonitrile polymer was prepared by the reaction between monomer and the curing additive 4-(aminophenoxy)phthalonitrile(APPH),which is also a kind of self-catalyzed monomer.The BCBP polymer might form phthalocyanine and isoindoline structures mostly as revealed by Fourier Transform Infrared spectra.The melting point of monomer is high(191 ~oC)and its processing window(64 ~oC)is not ideal enough.Different concentrations of APPH could lead to different crosslinking degrees and thus the properties of the BCBP resin were influenced distinctly.The polymer possessed high storage modulus(2.3 GPa),high glass transition temperature T_g(>400 ~oC),and excellent high temperature stability with low water uptake.All of these advantages prove that the introduction of pyridine take an obvious role of improving phthalonitrile performance.Since T_g and thermal decomposition temperature of epoxy is lower,epoxy is hard to meet the needs of application at high temperature and its more widely use has been limited.To raise the heat resistance of epoxy,a kind of naphthyl-based phthalonitrile with good processability was used to copolymerize with epoxy.DSC results indicated that the two monomers copolymerized successfully.DMA results revealed that addition of little phthalonitrile monomer bring distinct enhancement to T_g of copolymer,which made copolymer show outstanding mechanical and heat-resistance properties.TG measurement demonstrated that thermal stability of copolymer was increased evidently and possess good flame resistance.In order to investigate the influence of difference of molecular structures on phthalonitrile's performance,two sulphur-containing phthalonitrile monomers were synthesized and compared with traditional phthalonitrile monomers containing similar structure.The measurement results indicated that rigid moieties led a higher monomer melting point and a relatively narrow processing window,but flexible groups made an opposite effect.Monomers including electron-withdrawing group polymerized more readily but rapid curing would make reaction time shorter and viscosity higher,which is adverse to processing and aftertreatment.Meanwhile,monomer molecules containing flexible segment tend to achieve more fully polymerization and thus have better thermal stability.