Study On The Preparation And Performances Of Sulfonated Polyphosphazenes For Proton Exchange Membrane

Proton exchange membrane fuel cell(PEMFC)is a clean and high-efficiency device.Proton exchange membrane material,as the key component of PEMFCs,is the most urgent issue to solve in the fuel cells.Sulfonated polyphosphazene materials have attain so much attention duo to its some advantages,such as high proton conductivity,low methanol permeability and high thermal stability.Polyphosphazenes are macromolecules,having the alternating-N=P-structures in the main-chain.Due to their high-modification side-chain structures,we could introduce some special property groups into side-chain of polyphosphazene to achieve target materials with special properties.In this article,four novel polyphosphazene-based proton exchange membranes have been designed and prepared on the basis of polymer properties.A series of sulfonated poly(phosphazene)-graft-poly(styrene-co-N-benzylmaleimide)proton exchange membranes have been prepared based on linear polyphosphazene main-chain,followed by grafting with poly(styrene-co-N-benzylmaleimide)in the side-chain and sulfonation reaction.Through the tests of the properties of these sulfonated polyphosphazene membranes,the results show that these obtained membranes have high water uptake,low swelling ratio,high proton conductivity and low methanol permeability.In addition,compared with traditional sulfonated polyphosphazene membrane,the chemical and thermal stabilities of these membranes have been improved significantly.Transmission electron microscopy(TEM)test shows clear phase-separation structures in the membrane,which is effective for the formation of ion-channels.A new sulfonated poly(aryloxycyclotriphosphazene)polymer has been synthesized,taking hexachlorocyclotriphosphazene as monomer.A series of novel crosslinked sulfonated polyphosphazene membranes have been prepared by crosslinking this sulfonated polymer with main-chain sulfonated polyphosphazene.The results of properties tests show that the water uptake,proton conductivity and methanol permeability increase when the content of sulfonated polymer increases.However,the dimensional stability could maintain excellent due to the crosslinking structures,making the membranes low swelling ratio under the high water uptakes.TEM test also shows that these membranes have clear phase separation structures,which could provide ion-channels effectively.A series of sulfonated polyphosphazene with perfluorosulfonic acid/alkylsulfonic acid in side-chain have been prepared based on polyphosphazene main-chain.The results of properties tests of these membranes show that the sulfonated polyphosphazene with perfluorosulfonic acid in side-chain have the better water uptake and proton conductivity.TEM images of sulfonated polyphosphazene with perfluorosulfonic acid in side-chain shows more clear phase separation structures and ion channels,in turn to enhance the proton conductivity effectively.In addition,these membranes also have superiority in oxidative stability and thermal property.To achieve the polyphosphazene proton exchange membrane with high proton conductivity,perfluorosulfonic acid groups have been grafted into side chain of polyphosphazene structures,and crosslinked it with sulfonted(ether ether ketone)(SPEEK)to prepare a series of novel crosslinked sulfonated polyphosphazene membranes.In comparison with the membranes with similar IEC values,these membranes have higher proton conductivities and dimensional stabilities,excellent thermal and chemical stabilities.Compared with perfluorosulfonic acid Nafion membrane,the selectivity values of obtained membranes are higher than Nafion,showing better applications as proton exchange membranes.