Preparation And Properties Of Quinoxaline-based Maleimide And Its Composites

Maleimide resins,a class of polyimides,have been developed one of the most promising resins by tight structure,excellent thermal stabilities and heat resistance.However,the high cross linking density and rigidity make them reveal extremely stiffness,low impact strength.Thus,pure maleimide resins were often used with other material together to obtain high performance resin based composite.Over the past few decades,polybenzoxazines,as recently developed phenolic resins,have received much interest of academia and industries.They provide various attractive properties that cannot be afforded by traditional phenolic resins and epoxies such as excellent thermal stability,low flammability,near zero shrinkage upon polymerization,and low absorption of water.The polyimide,polyether,and polyester base on quinoxaline,containing a pyrazine ring attached to benzene,have provided with high glass transition temperature?T_g?,excellent mechanical properties and outstanding thermal properties.They have an important application in polymer blend and adhesive area.In this paper,a novel series of mono-,bis-,tri-,and bisphthalonitrile-containing quinoxaline-based maleimides?MQMI,BQMI,TQMI,and PhQMI,respectively?were successfully synthesized by the cyclodehydration of maleic anhydride and the corresponding amines,in which acetic anhydride and sodium acetate trihydrate were used as dehydrating agent and catalyst,respectively.The chemical structure,curing properties,and curing kinetics of the monomers were investigated by Fourier transform infrared?FTIR?,Hydrogen nuclear magnetic resonance?¹H NMR?,and Non-isothermal Differential scaning calorimeter?DSC?.The thermal properties of the cured resins were studied by Thermogravimetric analysis?TGA?.The results indicated that the activation energy of BQMI is lower than that of MQMI,which means the curing reaction of the maleimide ring attached with benzene had priority over the maleimide ring attached with quinoxaline ring.The P-a/MI polymer alloys possessed excellent radiation resistent property.A series of polymer alloys formed by mixing typical benzoxazine monomer,3-phenyl-3,4-dihydro-2H-1,3-benzoxazine?P-a?,and the novel quinoxaline-based maleimide?MI?.The curing behavior,thermal properties,thermal machanical properties,morphological properties,and flexural property were studied by DSC and FTIR,TGA,Dynamic mechanical analysis?DMA?,Scanning electron microscope?SEM?,and universal tensile testing machine,respectively.The results indicated that the curing temperature was decreased gradually with the increase of the quinoxaline-based maleimides loadings.Besides,the incorporation of quinoxaline maleimide improved the thermal properties of pure benzoxazine resin evidently.Besides,the benzoxazine end-capped fluorene-based poly?ether ketone ketone??BPEKK?was prepared.The curing behaviour,thermal properties,and thermal mechanical properties were studied.The BPEKK14 was choosen to modified the P-a/MI alloys,in which the molar ratio of BHK to BPA was 1 to 4.The thermal properties and mechanical properties of the blends were studied.The results indicated that the addition of the BPEEK improves the thermal properties and toughness of P-a/MI resins.The thermal and mechanical properties of BPEEK modified P-a/MI systems increased with the increasing of BPEEK content.Moreover,the improvement of the thermal stability for Poly?P-a/TQMI/BPEKK10?was the best among the blends.The T₅ and char yield was 360 ^oC and 53.8%,respectively.Interestingly,the flexural strength of Poly?P-a/BQMI/BPEKK20?reached 140 MPa.In addition,the introduction of BPEKK improved the toughness of the P-a/MI polymer alloys.Moreover,four types of nano fillers?ZnO,TiO₂,Si₃N₄,and BN?were used to mix with P-a/MI polymer alloys to prepare the P-a/MI-based composites.The curing behavior,thermal properties,thermal mechanical properties,and mechanical properties of the blends and composites were studied.The T_g values of P-a/MI-based composites system increased with lower nano filler content,then it tends to decrease slightly with the increase of the nano filler loadings.The thermal stability and machenical properties of the composites increased straightly with the increase of nano filler contents.Interestingly,the Y_c and flexural strength of Poly?P-a/PhQMI/SN10?reached 64.4%and 145 MPa,respectively.Besides,the composites have a typical toughness fracture structure characteristics.