Synthesis And Properties Of Polymers Containing Perfluorosulfonic Acids Or Fluoroazobenzenes

Fluoropolymers,introducing fluorine atoms into the chemical structure of the polymers,which have the unique properties because of the existence of fluorine,and have been widely used in the field of functional polymers.In recent years,with the development of “Ullmann” reaction,“Click” reaction,“living”/controlled radical polymerization and other methods,as well as the combination of high-efficiency organic reaction and polymerization,it has been provided a new way for the design of novel fluoropolymers.In this thesis,the unique properties of fluorine were introduced to design two types of functional fluoropolymer materials:On the one hand,utilizing the strong electron-withdrawing and the smaller atomic radius of the fluorine atom,the perfluoroalkyl and the sulfonic acids were connected to form a perfluorosulfonic acids structure(Rf-SO3H),and then introduced to the side-chains of the polymers.Firstly,fluorine is the most electronegative element,the direct connection of perfluoroalkyl and sulfonic acids produces a strong “field effect” and “inductive effect”,which greatly increases the acidity of sulfonic acids.Furthermore,it facilitates to increase the ability of the sulfonic acids to move freely due to the small atom radius of the fluorine and the better flexibility of the perfluoroalkyl.Therefore,the introduction of the strongly acidic,flexible perfluorosulfonic acids into the side-chains of the polymers facilitates the formation of hydrophilic/hydrophobic phase-separated structure within the polymer.The proton exchange membrane prepared by this polymer with excellent comprehensive performance can be applied to a fuel cell system.On the other hand,utilizing the smallmer atomic radius and low surface energy properties of the fluorine atom,the perfluorobenzene and the azobenzene groups were connected to form a perfluoroazobenzene structure,and then introduced to the polymers.Firstly,it improves the stability of azobenzene due to the small atomic radius of fluorine and the harder bend of planar structure of azobenzene.Moreover,fluorine has low surface energy characteristic,a light-regulated wettability surface can be prepared,which combines the hydrophobicity of the chemical structure of the fluoropolymers and the physical structure of the suface relief gratings(SRGs)of the azopolymers.The main research contents and conclusions are as follows:System ?: Synthesis of poly(arylene ether sulfone)bearing perfluorosulfonic acids and its application as a proton exchange membrane for fuel cells.A versatile and facile synthetic approach to poly(arylene ether sulfone)bearing perfluorosulfonic acid groups(PAES-PSA,IEC = 1.78 mequiv g-1)via polymer post-modification(PPM)is described,the structure and molecular weight of the polymers were successfully characterized by 1H NMR,19 F NMR,FT-IR,and GPC.Flexible,tough,and transparent membrane was obtained by polymer solution casting,exhibited excellent thermal stability,mechanical properties and moderate oxidative stability.Morphology observation by atomic force microscopy(AFM)and small angle X-ray scattering(SAXS)revealed that the PAES-PSA membrane held highly hydrophilic/hydrophobic phaseseparation and hydrophilic domains partly connected to each other,which was easy to form ion transport channels,ensuring good proton conductivity of the membrane.The membrane had a higher water uptake(58.6%)with swelling ratio only 23.9%,compared to Nafion(27.1%,12.9%,respectively)in hydrated state at 60 oC.Under full hydrated conditions,the proton conductivity of PAES-PSA membrane increased from 8.4 m S cm-2 to 158 m S cm-2 with the temperature was raised from 30 oC to 80 oC,which was always higher than Nafion membrane under the same test conditions.Applying PAES-PSA membrane to H2/O2 fuel cell system,the maximum power density was 300 m W cm-2 at 40 oC,400 m W cm-2 at 60 oC under 80% RH,with good battery performance but slightly weaker than Nafion.In summary,the PAES-PSA membrane could be used as a proton exchange membrane for fuel cells.System ?: Synthesis and properties of polymers containing fluoroazobenzenes in side-chain or main-chain.Through reversible addition-fragmentation chain transfer(RAFT)polymerization and condensation polymerization,two types of fluoroazobenzene-containing polymers were designed and synthesized,namely,main-chain fluoroazobenzene-containing polymer(Poly(PFAZO-(CF2)n),n = 4,6,and 8)and side-chain fluoroazobenzene-containing polymer(Poly(PFAZO-MA),Poly(PFAZO-MA)-RH,and Poly(PFAZO-MA)-RF),the structure and molecular weight of the polymers were successfully characterized by 1H NMR,19 F NMR,and GPC.Initially,the photoisomerization behavior of two types of azopolymers was investigated,the trans-to-cis isomerization under 313 nm or 365 nm UV light irradiation,the cis-to-trans isomerization under 435 nm purple light irradiation,and no isomerization under 546 nm green light irradiation for a short time,in particular,the photoisomerization process of Poly(PFAZO-(CF2)4)was accompanied by “blue shift” and “red shift”.Additionally,two types of azopolymers had a good surface hydrophobicity,the static water contact angles of the main-chain azopolymer(Poly(PFAZO-(CF2)n))increased from 99.17o(n = 4)to 110.26o(n = 6),138.67o(n = 8),the side-chain azopolymer(Poly(PFAZO-MA),Poly(PFAZO-MA)-RH,and Poly(PFAZO-MA)-RF)were 101.75 o,103.49 o,112.29 o,respectively.However,surface wettability could not be regulated by light irradiation.Finally,Poly(PFAZO-MA))formed a SRG with grating interval of 700-740 nm and modulation depth of 27-34 nm,after exposured to 3600 s with polarization laser interference,and its light-regulated wettability was preliminary investigated.