Preparation And Properties Of N-heterocyclic Sulfonated Poly(Aryl Ether Sulfone)s For Proton Exchang Membranes

With the increasing demand for energy in the new century,polyelectrolyte fuel cells（PEMFC）have attracted much attention as a clean energy source with high power density,high efficiency,fast start-up and portability,where the development of novel high-performance proton exchange membrane materials has become a research priority.Perfluorosulfonated membranes are being commercialised for their high proton conductivity and excellent oxidative stability,but they are unable to be used at high temperatures,and their unfavourable dimensional stability with high costs further limits their development.Sulfonated poly（arylene ether）s（SPAEs）are the most promising materials for proton exchange membranes due to their ease of molecular design and modification,excellent thermal and mechanical properties,and low cost.However,existing SPAEs exhibit poor oxidative stability due to their high content of ether bonds in the main chain,and are also limited by their insufficient proton conductivity.In this paper,a series of novel poly（arylene ether sulfone）s containing diphenyl-biphthalazin-dione moieties were designed and synthesized from the perspective of molecular design,and the thermal and mechanical properties of the poly（arylene ether）s were enhanced by introducing diphenyl-biphthalazin-dione moieties.A series of sulfonated poly（arylene ether sulfone）s were modified to reduce the probability of radical attack by reducing the content of ether bonds in the main chain,so as to improve oxidation stability;the ability to construct proton transport channels was enhanced by preparing block sulfonated poly（arylene ether sulfone）s films to improve proton conductivity,while further enhancing oxidation stability.a series of novel poly（arylene ether sulfone）s containing diphenyl-biphthalazin-dione moieties（PPDESs）were prepared by copolymerization of 4,4’-diphenyl-6,7’-biphthalazin-1,1’（2H,2’H）-dione（DBD）,（4-hydroxyphenyl）-2,3-diazanonaphthalen-1-one（DHPZ）and 4,4’-dichlorodiphenyl sulfone（DCS）as monomers.The structure and composition of the PPDESs were characterized by ¹H-NMR,FT-IR,XRD and GPC.The glass transition temperature of PPDESs ranged from 325-388°C and the 5%mass loss temperature in N₂ from 503 to 513°C,showing better thermal resistance with increasing DBD content;the Young’s modulus ranged from 1.95-2.16 GPa,the tensile strength from 107-119 MPa and the modulus retention from51.6-57.2%at 300°C.The diphenyl-biphthalazin-dione moieties conferred excellent thermal and mechanical properties to the PPDESs.The sulfonated poly（arylene ether sulfone）s containing diphenyl-biphthalazin-dione moieties（SPPDESs）were prepared in the IEC range of1.02-1.73 mmol/g,and the respective proton exchange membranes were prepared by the solution casting method.the water absorption of the SPPDESs membranes at 80°C ranged from13.3-35.2%,and the swelling ratio ranged from 6.7×7.2%-12.0×12.5%,with the rigid backbone limiting the swelling behaviour and showing promising dimensional stability.Due to the elimination of partial ether bonds in the backbone,SPPDESs membranes showed better oxidative stability than conventional SPAEs with breaking times ranging from 3.9-5.5h and dissolved times ranging from 8.4-10.3h in Fenton’s reagent at 80°C.The proton conductivity of the SPPDESs membranes was between 11.77 and 175.26 m S/cm and the proton conductivity increased with IEC at the same temperature,with SPPDES-6 membrane showing proton conductivity close to that of Nafion membrane at high temperatures.Block poly（arylene ether sulfone）s containing diphenyl-biphthalazin-dione moieties（Block-PPDES,or B-PPDES for short）were prepared by the"two-pot“method,and the structures of the oligimer and block copolymers were characterized by ¹H-NMR,FT-IR,and GPC.The block sulfonated poly（arylene ether sulfone）s containing diphenyl-biphthalazin-dione moieties（B-SPPDESs）were prepared in the IEC range of 1.00-1.71 mmol/g and the corresponding proton exchange membranes were prepared.The swelling ratio of B-SPPDESs membranes was lower compared to SPPDESs membranes because the hydrophobic phase interconnections counteract some of the plasticising effect of water.The breaking time of B-SPPDESs membranes at 80°C ranged from 4.2-6.6 h and the dissolved time from 8.8-10.9 h.Due to the placement of the ether bond,which is susceptible to radical attack,in the hydrophobic phase,the oxidation resistance was better than that of SPPDESs membranes.The proton conductivity of the B-SPPDESs membranes was also higher at the same temperature and humidity,with a proton conductivity of 187.41 m S/cm measured at 95°C for the B-SPPDES-6 membranes,demonstrating that the preparation of block sulfonated poly（arylene ether sulfone）s can effectively improve the oxidation stability and proton conductivity of the proton exchange membranes.