Researches On The Influences Of The Heteroatoms On Benzoxazine Resins And The Properties Of Polybenzoxazine-based Carbon Materials

As one of brand-new thermosetting resins,benzoxazine resin has been attracted a great deal of attention because of its extraordinary properties.However,there are also many problems unresolved in benzoxazine chemistry,for example the influences of substituents both on curing behaviors of benzoxazine monomer and H-bonds formation of corresponding polybenzoxazine should be considered as a whole,unfortunately,the two problems are often be investigated in a separated manner and lacking of a unified understanding.Furthermore,the application fields of the benzoxazine resin are also in a rather narrowed state.Ever since the start of the 21st century,mankind has been facing the problems of fossil resources depletion and environment deterioration.In this situation,systematically replace the petroleum-based polymers with bio-based ones both demonstrates the economic values and scientific meaning.In this situation,this thesis firstly explored the effects of the heteroatom substituents both on curing behaviors of benzoxazine and on H-bond system in polybenzoxazine,and then carbons rich in heteroatoms were prepared via chemical structure designed benzoxazine precursors.Based on the obtained carbon materials,a type of green energy storage device,supercapapcitor,was successfully fabricated,and thus the application fields of benzoxazine have been expanded successfully.In detail,the primary research contents and conclusions of the thesis are as follows:Firstly,taking advantage of flexibility of chemical structure design of benzoxazine,three model difunctional benzoxazines(BPT-an,BPS-an and BPAF-an)containing different heteroatom substituents(bridge groups)were synthesized to systematically explored the effects of heteroatoms on two core problems in benzoxazine chemistry(curing behavior and H-bond system).The results show that the electron-donating natured heteroatom makes benzoxazine monomer easy to initialize the polymerization but the polymerization proceeds in a rather slow manner,while the influence of electron-withdrawing natured heteroatom is exactly opposite.In addition,electron-withdrawing natured heteroatom can promote formation of phenolic Mannich bonds in polybenzoxazine,while electron-donating natured heteroatom can promote the formation of arylic Mannich linkages.In addition,the results also demonstrate that the electron-withdrawing heteroatom,especially when it can establish H-bond with phenolic hydroxyl group,such as O,F etc.,the heteroatom can effectively diversify and complicate the H-bond systems in polybenzoxzaine,and the thermo-mechanical performances of obtained polybenzoxaine can also be enhanced accordingly.Secondly,taking bio-based monomer vanillin as the raw material,two bio-based benzoxazine monomers(Boz-Va and Boz-bis-VaCN)was carefully designed and synthesized.Moreover,the cyano groups were introduced into the chemical structure of Boz-bis-VaCN via Knoevenagel reaction.Based on Boz-Va and Boz-bis-VaCN,two series of nitrogen and oxygen co-doped carbon materials(NOPC-x and NOPC-bis-CN-x)were obtained after carbonization and activation processes.The results demonstrate that the NOPC-bis-CN-x exhibit higher degrees of graphitization,larger specific surface areas,more desired pore structures and more excellent electrochemical performances than these of NOPC-x.Especially the NOPC-bis-CN-3 displays many distinguished properties,such as high specific surface area(2347 m² g^-1),large number of mesopores,distributed N and O active species on its surface,and so on.In a three-electrode system,the NOPC-bis-CN-3 displays mass specific capacity of 167.3 F g^-1,when 1 A g^-1 of current density is applied.In addition,a symmetrical supercapacitor was constructed using NOPC-bis-CN-3 as the electrodes,and its energy density only decreases from10.8 Wh kg^-1 to 9.0 Wh kg^-1 when the power density increases from 45 W kg^-1 to 4500W kg^-1.In short,by introducing more nitrogen heteroatoms into the chemical structure of benzoxazine,the electrochemical performance of its carbon residue was significantly improved,and finally a green energy storage device with excellent electrochemical performance was prepared in this study,and the purpose of enhancing the electrochemical performances of the carbon residue of the benzoxazine resin has been successfully achieved by doping more nitrogen heteroatoms to benzoxazine resin.Thirdly,a bio-based benzoxazine SA-a containing N,O,and S heteroatoms was obtained using a bio-based monomer furfurylamine as the raw material.Furthermore,with the bio-based benzoxazine,PAN,and Fe(acac)₃,a type of brand-new carbon nanofiber Fe₃O₄@SNOCNFs containing N,O,S and Fe₃O₄ was prepared via electrospinning method.Compared with the nanocarbon fiber CNFs prepared by electrospinning of pure PAN,adding benzoxazine can significantly improve the flexibility of the CNFs,and even after depositing Fe₃O₄ on the surface,the flexibility of the obtained nanocarbon fiber will not be reduced,making it an ideal material for fabrication of flexible supercapacitors.A three-electrode system was established by taking Fe₃O₄@SNOCNFs as the working electrode,Pt electrode as the counter electrode,Hg/Hg O as the reference electrode,and 6 M KOH as the electrolyte.The results show that Fe₃O₄@SNOCNFs display good EDLC characteristics and pseudo-capacitance characteristics at the same time,and with the synergistic effects of EDLC and pseudo-capacitance,the mass specific capacity of Fe₃O₄@SNOCNFs reached to160 F g^-1 when a current density of 1 A g^-1 was applied.Finally,inspired by the H-bonds in benzoxazine can effectively enhance the thermomechanical properties of the polybenzoxazine,a bio-based epoxy monomer EP-F was synthesized from the bio-based platform compound 2,5-furandicarboxylic acid.Moreover,a petroleum-based epoxy monomer EP-B was also prepared as the control.The results demonstrate that with the same curing agent(DDM)and the curing techniques,the EP-F/DDM exhibits more excellent thermo-mechanical properties than the EP-B/DDM,including higher storage modulus,higher glass transition temperature T_g.In addition,it should be noted that although there are more heteroatoms(oxygen atoms)in EP-F/DDM than in EP-B/DDM,the polar component?_s^p of EP-F/DDM is only 16.6,which is lower than that of EP-B/DDM(17.2),indicating that the hydroxyl groups appeared in EP-F/DDM after curing reaction had been shielded via forming the H-bonds with oxygen atoms in furan rings.Moreover,the elimination of H-bonds by bromination also proved that the desired thermo-mechanical properties of the EP-F/DDM were derived from its more and diversified H-bonds.