Curing Behaviors Of Phthalonitrile-based Resin Containing Benzoxazine And Their Properties

Phthalonitrile containing benzoxazine is a novel phthalonitrile-based resin that was designed and prepared recently,aiming for combining both the outstanding properties of phthalonitrile and benzoxazine.The novel resin exhibited not only the excellent mechanical and flame retardant properties derived from phthalonitrile resin,but also the autocatalytic reaction characteristics of benzoxazine,which obviously made up for the shortage including difficult processing and high post-curing temperature of phthalonitrile-based resins,showing great application potential and values.Thus,to further understand the curing behaviors of phthalonitrile containing benzoxazine monomer and their properties,the reaction kinetics were first studied to reveal the curing process,and then,the model compounds were designed and employed to investigate the polymerization mechanisms of phthalonitrile containing benzoxazine resin;followed,the catalyzed polymerization and co-polymerization of phthalonitrile containing benzoxazine were studied;then,the application values of phthalonitrile containing benzoxazine as one high performance polymer were discussed through the preparation of glass fiber reinforced composites and functional complex.First,the phthalonitrile containing benzoxazine monomer was prepared via solution reaction with amino-substituted phthalonitrile monomer,bisphenol A and paraformaldehyde as the initial materials.The dymatic and non-isothermal DSC tests were performed to investigate the cuirng behaviors of the monomers,and then,isoconversion methods and model-fitting methods were employed to discuss the curing kinetics.Results indicated that thecuring of phthalonitrile containing benzoxazine was consisted of two main autocatalytic polymerizations,corresponding to the ring-opening polymerization of benzoxazine and ring-forming polymerizationa of nitrile groups,and their reaction energy were 90.6KJ/mol and 102.2KJ/mol.The kinetic equations of the two autocatalytic reactions were obtained.Second,it was found that the polymerization of nitrile groups was determined by the ring-opening of benzoxazine rings.Thus,model trials were designed to reveal the curing mechanisms of phthalonitrile containing benzoxazine.Resulting indicated that the Mannich structures with phenol type,containing phenol hydroxyl and imine covalence structure,would significantly promote the polymerization of nitrile groups,while the single phenol hydroxyl couldn't accelevate the polymerization of nitrile directly.Through the investigation and discussion of the curing behaviors and processes between bisphenol A,N,N-dibenzylaniline,benzoxazine dimer and bisphenol A type phthalonitrile resin,the polymerization of nitrile groups were supposed as the Thorpe and Thorpe-Zielger reactions.Then,to understand the catalytic polymerization of phthalonitrile containing benzoxazine and its properties,bisphenol A and allyl bisphenol A were introducted into the matrix.Results of reaction kinetics indicated that phthalonitrile containing benzoxazine/bisphenol A?BA-ph/BPA?system exhibit triple autocatalytic reactions and the reaction energy decreased with the introduction of bisphenol A,as well as the intial curing temperature,which was decreased from 180?C to 120?C.The rheological behavior indicated that the low viscosity and wide processing temperature range were ascribed to the introduction of bisphenol A.Moreover,double glass transition processes were observed during the investigation of therma-mechanical properties,corresponding to the microsphase seperation during the polymerization of benzoxazine and nitrile groups,which were confirmed by SEM images.Results of the curing and rheological behaviors of phthalonitrile containing benzoxazine/allyl bisphenol A?BA-ph/DABPA?indicated that the polymerization of the system was accelerated by DABPA,also,the processing temperature range was widen?50²00?C?.Additionally,the thermal properties of BA-ph/BPA and BA-ph/DABPA polymers were T_5%>410?C and T_5%>410?C,respectively.The copolymerization of phthalonitrile containing benzoxazine with epoxy?EP?and a novel low viscosity phthalonitrile?NP-ph?resin were studied to understand the copolymerization process and their properties of the copolymers.Results indicated that the introduction of epoxy resulted to a triple reaction process,and the polymerization of epoxy firstly occurred at 150²00?C,then the copolymerization of benzoxazine and EP and the ring-forming polymerization of nitrile groups occurred consecutively.Due to the copolymerization and diluent effect,low viscosity and good processing propertities at 180²00?C?1min<tgel<42min?were obtained for BA-ph/EP system,which can be controlled by varying the content of EP and the processing temperatures.In comparison with that of BA-ph/EP,results of BA-ph/NP-ph indicated that the introduction of NP-ph did not significantly hinder the polymerization of both benzoxazine and nitrile groups,and the double curing peak temperature occurred at 225²40?C and 265²73?C.Moreover,BA-ph/NP-ph exhibited a continuous and fragment-free reaction process,alleviating the central heating phenomenon during the polymerization.BA-ph/EP and BA-ph/NP-ph copolymers both showed outstanding thermal stabilities,and the thermal propertiy of BA-ph/NP-ph copolymer(410?C<T_5%<430?C)was better tha that of BA-ph/EP(390?C<T_5%<420?C).The glass transition temperatures of various BA-ph/NP-ph copolymers were higher than 360?C,showing good thermal mechanical properties.Finally,the reinforced and functional composites were obtained by preparing fiber-reinforced lamination and introducing the magnetic hybrid microsphere into the matrix.A series of phthaolonitrile containing benzoxazine based composites with mechanical strength?660MPa?and modulus?28.6GPa?,as well as good thermal performance(T_5%>430?C)were prepared;besides,a kind of electromagnetic materials based on the high performance BA-ph composites with good electromagnetic absorption intensity?25dB?were obtained.In sum,the enhancement and functionalization of BA-ph resin can be implemented.