Thermoplastic Interpenetrating Polymer Networks Based On Polybenzimidazole For Anion Exchange Membranes

As the key component of anion exchange membrane fuel cell,high conductivity,good mechanical and chemical stability anion exchange membrane?AEMs?become the research emphasis of anion exchange membrane fuel cell.In this thesis,a new series of thermoplastic interpenetrating polymer network?TIPN?anion exchange membranes with high ionic conductivity and excellent dimensional stability based on poly [2,2'-?p-oxydiphenylene?-5,5'-bibenzimidazole]?OPBI?and has been developed.With 1,2-dimethyl-3-?4-vinylbenzyl?imidazolium chloride?DVIm?polymerization in presence of OPBI polymer chains,two kinds of uncrosslinked polymer chains,PBI/DVIm TIPN membranes were prepared.Optimal preparation proportion was PBI/DVIm=2:1.PBI/DVIm TIPN-4/2 membrane exhibits high hydroxide conductivity(86.7 mS cm^-1)and the swelling ratio is 10.5% at 80 oC.Compared with DAIm membrane in same level alkali uptake,small steric hindrance effect of the DAIm monomer and non-covalent crosslinking interpenetrating polymer chains contribute to better compatibility and chains flexibility in the PBI/DAIm TIPN membranes achieve well-balanced performance between high hydroxide conductivity and dimensional stability because of the dynamically forced compatibility feature of TIPN.With 1,2-dimethy-3-allylimidazolium?DAIm?polymerization in presence of OPBI polymer chains,two kinds of uncrosslinked polymer chains,i.e.PDAIm and OPBI interpenetrate with each other to form a physically crosslinking network.The IEC of PBI/DAIm TIPN ranged form 0.30 to 0.62 mmol g^-1.Especially,the PBI/DAIm TIPN-65/0.5 membrane exhibits high hydroxide conductivity(96.7 mS cm^-1)and low swelling ratio?4.4%?at 80 oC.With very low overall alkali uptake?2.89%?,it exhibits excellent chemical stability in 1M KOH at 60 ? for 96 h?94.0% retention?and high tensile strength?48.2 MPa?in hydrated state.These observations suggest TIPN structure provides a promising solution to the electrochemical-mechanical balance of AEMs.Semi-interpenetrating networks?PBI/DAIm sIPN?and Blend?PBI/DAIm Blend?membranes based on OPBI and DAIm with 0.25wt% initiator dosage and 65wt% monomer initial concentration were prepared.TIPN compared with the blend and semi-interpenetrating networks,which are evidenced by SEM and SAXS,promote the aggregation of hydrophilic groups and induce connective ionic conductive channels.Hydroxide conductivity of TIPN,Blend and s IPN membranes are 59.3 mS cm^-1,47.5 mS cm^-1 and 33.6 mS cm^-1,respectively.Because of the dimensional stability based on interpenetrating networks structure,TIPN and sIPN membranes exhibit lower swelling ratio?2.3% and 3.3%?of Blend membrane?7.7%?.