The Preparation And Properties Of Biphenyl-type Phthalonitrile-based Resin And Their Reinforced Composites

4,4’-bis(3,4-dicyanophenoxy)biphenyl(BPh)is an important high performance thermosetting resin,which is mainly through the polymerization of cyano groups to form of a stable polymer network.The resin has outstanding thermal resistance,mechanical properties,flame-proofed property and moisture resistance.It is in great demand in aerospace and marine applications.Thermosetting resins have high glass transition temperature(Tg),excellent electrical performance,small volume shrinkage,low water absorption and superior thermal stability which are called high performance thermosetting resins.The most common state-of-the-art high performance thermosetting resins are cyanate,benzoxazine,polyimides and phthalonitrile.Cyanate and benzoxazine resin are the resins which can cure at low temperature and easy to process,but due to the influence of ether bond,the Tg is not too high and almost around 300 oC.The high processing temperature of polyimides limited its applications to a great extent.Phthalonitrile resins,in recent years,as a class of high performance thermosetting resin has attracted increasingly attention due to the outstanding thermal stability and excellent mechanical property.Similarly,as traditional phthalonitrile-based resins,the high processing temperatures and inert reactions are still the key problems for the further applications.On this basis,the research basises on modification of BPh by thermoplastic resin toughening,molecular design and copolymerization.Spcecific methods are as follows:(1)In order to solve the toughness of BPh,hydroxy-terminated poly(arylether nitrile)(PEN-OH)is selected as the toughten matrix,the research on tougtening and modification effect of BPh on PEN-OH is conducted.At different curing temperature,the study has shown the interrelationship between PEN-OH and BPh,which provide a new idea for toughening research.(2)In order to avoid the drawback of high melting temperature of BPh,we synthesized bisphthalonitrile oligomer with arylether nitrile linkages(n=1)between the terminal phthalonitrile groups(EN-BPh),which has low melting temperature(150oC)and low curing reaction rate.(3)The aromatic amine curing agents for phthalonitrile resin have low decomposition temperature,which will cause defects in the internal sturcture of resin at high curing temperature,and the mechanical properties will certainly be influenced.In order to solve this problem,the benzoxazine-containing phthalonitrile(BA-Ph)is adopted to blend with EN-BPh so as to improve the performance of the resin.The results show that the copolymer system had low viscosity at 120 oC and the processing temperature window is 60 oC indicates a good processing performance.(4)EN-BPh/BA-Ph/glass fiber compistes are prepared and its mechanical properties,dynamic mechanical properties,water absorption and dielectirc properties are studied.The results indicated that the EN-BPh/BA-Ph/GF 55 exhibits good mechanical properties and dynamic mechanical properties.