Curing Behavior And Functionalization Of Nitrile-based Polymers

Phthalonitrile resin is a type of thermoset possessing phthalonitrile moieties,which could transform into highly crosslinked structures via nitrile additions through high temperature and suitable catalyst treatment.This curing process did not lead to small volatiles releasing,and corresponding cured polymers exhibited excellent heat resistance,flame retardance,chemical and water resistance and good mechanical performance,which showed great potential in aerospace,mechanics,electronics and aviation fields.However,due to nitrile group's intrinsic low reactivity,high temperature and prolonged time were required for the curing of the resins.Which led to the great difficulty of their composite fabrication,then the industrial applications were severly hindered.Besides,these resins were commonly adopted as resin matrix for fiber reinforced composites.Insufficient efforts were devoted to other functional applications.In order to overcome the processability difficulties,acetylacetonate salt catalysts were selected as the curing catalysts for phthalonitrile resin,and resin systems with good processability and thermal properties were also designed and synthesized.Furthermore,various inorganic additives were introduced into the phthalonitrile resins,as a result,the thermal stability and corrosion resistance were siginificantly enhanced,and in addition,processable powder coatings were acquired.Detailed research is stated as follows:(1)Three acetylacetonate salt catalysts were selected as curing catalysts for the curing of phthalonitrile resin,and the curing reactivity and the thermal properties of the cured polymers were studied.The curing mechanism of three catalysts followed the same manner,generating triazine,isoindoline and phthalocyanine structures.Copper acetylacetone(Cu(acac)₂)could lower the reaction temperature,and the corresponding cured polymer exhibited good themal stability and oxidation resistance.The required activation energy for aluminum acetylacetone(Al(acac)₃)was the lowest(69.8 k J/mol),its cured polymers also displayed good thermal performances,which laid good foundation for the further functional application studies.(2)Two kinds of lamelleted inorganic fillers were introduced into phthalonitrile resin,and the thermal stability and corrosion resistance of the hybrid composite/coating were then evaluated.Boron nitride/nitrile based resin(h-BN/MPN)displayed the best thermal stability(higher than 450^oC),and the adhesion and hardness of the cured coating met the demand for high-temperature applicaions.Electrochemical analysis revealed that the protectiove efficiency of h-BN/MPN for SS304 stainless steel reached 98%.(3)The comprehensive performance for h-BN/MPN hybrid coating was achieved by adjusting the contents of h-BN.SEM images indicated that adequate filler connection was formed within h-BN/MPN composite with 30 wt%amount of h-BN hybrid,and at the same time,the adhesion and hardness of the obtained coating reached the maximum.Such hybrid coating could withstand 450^oC treatment for long time under air atmosphere.Correspondingly,the coatings displayed enhanced ion shielding,significantly improving the protection effect for SS304 stainless steel.The study has not only explored the curing catalysts for phthalonitrile resins,but also developed a series of functional hybrid coating with excellent heat and corrosion resistance,which gave a good contribution to the development of phthalonitrile resins.