Design And Preparation Of Heat Resistant Resin System For POSS Modified Phthalonitrile And Its Modifying Mechanism

Phthalonitrile polymers widely used in aerospace,shipbuilding and other fields due to their excellent heat resistance,ablation resistance and flame retardancy highly attracted the attention of scholars at home and abroad.In recent years,researchers committed to improve processing window of phthalonitrile polymer by synthesizing new monomers with flexible groups,grafting to copolymerize or blending with other resin to lower the melting point and to improve fluidity,but this improving is often at the expense of heat resistance and mechanical properties of the resin itself.This subject has systematically studied this problem.The phthalonitrile polymer,the EP0408 and AM0281-phthalonitrile polymers were constructed by using Materials Studio software.Molecular dynamics simulations were carried out respectively from 300 K to 1200 K with the Dynamics of Forcite module.Tg temperature respectively was obtained.The simulation results show that the glass transition temperature of the EP0408 and AM0281-containing polymers was increased dramatically,respectively from original 455°C for the neat polymer to 799°C and 501°C.Two kinds of curing agents,4,4'-bis(4-aminophenoxy)biphenyl(BAPP),3,3'-diamino-4,4'-dihydroxydiphenyl sulfone(AHPS),were selected to prepare and optimize BPH-BAPP and BPH-AHPS polymers and their composites respectively.The kinetic parameters,thermal property,micro-structure of the prepolymers and polymers,dynamic mechanical properties and mechanical properties of the two formulations were studied by using DSC,TGA,DMA,infrared and mechanical tests.The research shows that BPH-BAPP system exhibits higher thermal property.Two kinds of POSS,AM0281(with amine group)and EP0408(with epoxy group),were used to prepare POSS modified BPH-BAPP polymers and composites.And they were characterized by DSC,TGA,DMA,SEM,IR,rheology,water absorption and mechanical tests.The kinetic parameters,thermal properties,mechanical properties,microstructure,surface morphology,rheological properties and water absorbency of two doped systems were studied and compared.The results show that the glass transition temperature of POSS modified phthalonitrile polymers is above 400°C.EP0408 containing polymers have better thermal property,especially when the amount of EP0408 was 0.5%,the retention at 900°C is 48%,better than the value 40% when the amount of AM0281 was 1%,however,the retention at 900°C of the neat polymer is only 31%.Interlaminar shear strength of POSS-containing polymers at room temperature is 86.7MPaand 90.1MPa,much higher than the neat polymer's 77.7MPa.The neat polymers and the EP0408-0.5 polymers were respectively exposed at 500°C,600°C and 800°C for about 3 hours,and the samples before and after aging tests were characterized by TGA,DSC,TGA combined with FTIR,FTIR,XPS,XRD.The results show that the EP0408-0.5 polymers have better thermal stability than that of the neat polymer.The reason why the POSS-containing polymers have improved thermal stability may that the POSS with high stiffness structure improves the overall stiffness of the polymer chain,at the same time,the intermolecular force is also increased by chemical bonds and hydrogen bo nds in the system.These effectively prevent the thermal motion of the polymer chain in the high temperature.Thus the fracture of the bond is suppressed and the thermal stability is increased.In order to improve phthalonitrile resin,POSS modified phthalonitrile polymers blended with cyanate ester resin and composites were prepared and characterized by DSC,TGA,DMA,IR,rheological test,mechanical test for their prepolymers,polymers and composites.The chemical reaction activity of different blends were studied and kinetic parameters,thermal properties,mechanical properties,microstructure and rheological properties were compared.The results show that the glass transition temperatures of the blends were all above 400°C,wherein the resin system containing 20% phthalonitrile polymers has best thermal property,low viscosity at room temperature,and good processing.