Preparation And Properties Of Proton Exchange Membranes Based On Side-chain Type Fluorinated Poly(Arylether)S Bearing Sulfonated Naphthanoxyl Pendants

Proton exchange membrane is one of the key components for the polymer electrolyte membrane fuel cell, which requires high conductivity, thermal and chemical stability, mechanical toughness as well as low cost. Borrowing ideas from the unique structure of perfluoro-hydrophobic backbone and sulfonated hydrophilic side chain for perfluorosulfonic acid membranes, several types of side-chain type sulfonated partially fluorinated poly(aryl ether) copolymers were developed. These copolymers were synthesized by introducing sulfonated naphthanoxyl pendants to the partially fluorinated poly(aryl ether) backbone, and subsequently converted into membranes through solution casting and characterized.Firstly, a series of novel side-chain type partially fluorinated sulfonated poly(ether sulfone)s (sSPFAES) copolymers were successfully synthesized by nucleophilic substitution reaction from 4,4’-dihydroxylbiphenyl sulfone,4,4’-biphenol, decafluoro biphenyl and disulfonaphthanol (2-naphthol-6,8-disulfonic acid dipotassium salt or 1-naphthol-3,6-disulfonic acid disodium salt).’H NMR and FTIR spectra confirmed the successful attachment of the disulfonaphthanoxyl pendants to the copolymer backbone. Ion exchange capacities (IECs) of the sSPFAES membranes determined by acid-base titration were about 1.28-1.73 mmol/g, all were tough and ductile, exhibiting Young’s modulus higher than 1.0 GPa, tensile strength of 20-37 MPa and elongation at break of 10-64%. They also showed good thermal and oxidative stability, the weight losses were lower than 5% at 320-360℃ in TGA tests and less than 7%　after treated with Fenton’s reagent at 80℃ for 1 h. The water absorbing and swelling behavior tests indicate that the obtained sSPFAES membranes had rather low water uptakes and good dimensional stability, with water uptake of 30-68%, swelling ratios below 17%　at the testing temperature range of 30-90℃. They all also showed good proton conductivity higher than 135 mS/cm at 80℃.Secondly, a series of novel proton exchange membranes derived from side-chain type partially fluorinated sulfonated poly(aryl ether) (sSPFAE) copolymers were successfully prepared, while the copolymers were synthesized through similar procedure as mentioned above but replacing 4,4’-biphenylsulfone with rigid and bulky 9,9’-biphenylfluorene. The obtained sSPFAE membranes had IECs about 1.27-1.65 mmol/by titration, all were tough and ductile with Young’s modulus higher than 1.0 GPa and elongation at break of 65～105%. They exhibited water uptake in the range of 21-51%, swelling ratios below 7%　at 30-90 ℃, weight losses less than 3% after treated with Fenton’s reagent at 80℃ for 1 h, and high proton conductivity of 50-250 mS/cm. At the meantime, this series of membranes displayed quite good hydrolytic stability, keeping rather high mechanical toughness and proton conductivity after aging in water at 140℃ for 16 d.Finally, a series of proton exchange membranes derived from side-chain type partially fluorinated sulfonated poly(aryl ether) with IECs about 1.20 and 1.50 mmol/g were prepared through similar procedures by altering the aromatic diphenol monomers. The property comparison results indicated that the more flexible the copolymer backbone, the higher water uptake, membrane swelling ratio and proton conductivity for the obtained membranes, while the more rigid the copolymer backbone, the better oxidative stability for the obtained membranes. On the premise of satisfying the proton conductivity requirement, the membranes derived from copolymers with both fluorenyl and biphenyl moieties in the copolymer backbones showed the best comprehensive performance for fuel cell applications.