Preparation And Properties Of Phthalonitrile/Hyperbranched Benzoxazine

In the present paper,four novel hyperbranched benzoxazines,which were synthesized by reacting the bisphenol-A,bisphenol-AF,hydroquinone and allyl bisphenol-A with polyether triamine（T-403）and paraformaldehyde,were bisphenol-A based hyperbranched benzoxazine（HB-TBA）,bisphenol-AF based hyperbranched benzoxazine（HB-TBF）,hydroquinone based hyperbranched benzoxazine（HB-TH）,and allyl bisphenol-A based hyperbranched benzoxazine（HB-DBA）,in the meantime,two kinds of phthalonitrile monomers were prepared by reacting the p-methylphenol and nonyphenol as phenol sources with4-nitrophthalonitrile:p-cresol type phthalonitrile（PPN）and nonylphenol type phthalonitrile（NPN）.The structures of HB-TBA,HB-TBF,HB-TH,HB-DBA,PPN,and NPN were characterized using the Fourier transform infrared spectroscopy（FT-IR）and nuclear magnetic resonance spectroscopy（¹H NMR）,while the differential scanning calorimetry（DSC）and FT-IR analyses were carried out to explore the polymerization of hyperbranched benzoxazine,phthalonitrile/phenol-anilinobenzoxazine（P-a）andphthalonitrile/P-a/hyperbranched benzoxazine resin systems.The dynamic thermomechanical and thermal properties of the above cured resin systems were investigated using the dynamic thermomechanical analyzer（DMA）and thermogravimetric analyzer（TGA）.The universal material testing machine and scanning electron microscope（SEM）were performed to undersand the mechanical behavior and morphological properties.By using the anhydrous potassium carbonate as a catalyst and the dimethyl sulfoxide（DMSO）as a solvent,the PPN and NPN monomers were obtained by the nucleophilic substitution reaction at 80℃ for 24 h.The yield of the product was about 80%;The P-a was used as a curing agent and diluent for phthalonitrile monomers to prepare PPN/P-a and NPN/P-a copolymers.The addition of P-a to PPN and NPN promoted the cross-linking reaction of cyano groups at a certain temperature,and the processability of the copolymers was greatly improved.The glass transition temperature（T_g）of the cured PPN/P-a and NPN/P-a resins was in the range of 240～300℃,the initial degradation temperature corresponding to 5 wt%weight loss（T₅）was recorded between 390 and 420℃,and the residual carbon ratio（Y_c）was measured between 53%and 64%at 800℃.Four new types of hyperbranched benzoxazines were synthesized by Mannich condensation reaction using the bisphenol-A,bisphenol-AF,hydroquinone and allyl bisphenol-A,and T-403 as A2 and B3 monomers and chloroform as solvent,respectively.The hyperbranched benzoxazines have an average molecular weight（M_n）between 3000 and 11000,the weight average molecular weight（M_w）between 5000 and 30000,and the molecular weight distribution coefficient（PDI）between 1 and 3.In addition,the synthetic hyperbranched benzoxazines exhibit a good solubility in a variety of polar organic solvents（chloroform,DMSO,tetrahydrofuran,etc.）,among which the HB-TH and HB-DBA were identified to be viscous at room temperature.The hyperbranched benzoxazines were capable of self-curing reactions and the processing window is wider.The as-prepared hyperbranched benzoxazine cured products have the T_g between 200 and 260℃,the storage modulus（E’）between 2000 and 2400 MPa,the T₅ was between 240 and 275℃,and the Y_c measured between 20%and 41%at 800℃.As a modifier of phthalonitrile,the curing peak temperature of phthalonitrile decreased with the increase of hyperbranched benzoxazine content.When the content of HB-TBA,HB-TBF,HB-TH and HB-DBA reached 12 wt%,the curing peak temperature of PPN decreased by 6～10℃,and the curing peak temperature of NPN decreased by 12～16℃.With the increase of hyperbranched benzoxazine content,the Tg of the copolymer gradually decreased.For illustration,the Tg of Poly（NPN/P-a）and Poly（PPN/P-a）decreased,respectively,by 4～14℃,and 14～20℃.At the same time,the initial degradation temepraures in terms of T5,T10,and Yc of the copolymer slightly decreased with the increase of the content of hyperbranched benzoxazines.The bending test results revealed that the flexural strength and modulus of the copolymer showed a decreasing trend.Compared with the phthalonitrile/P-a copolymer,the fracture surface of the phthalonitrile/P-a/hyperbranched benzoxazine copolymer was relatively rough with that the fact that no phase separations took place.In addition,the toughness（in situ toughening）of the phthalonitrile resin is improved.