Preparation, Charaterization And Performance Of Novel Polyphosphazene Membranes For Alkaline Fuel Cells

Novel polyphosphazene resin carrying quaternary phospaoniumgroups were prepared from poly（4-methyl phenoxy）phosphazene （P4MPP）by NBS bromination reaction, quaternary phosphonium reaction andalkalization reaction. The structure of all intermediates were characterizedby IR and NMR spectroscopy. Three membranes including purepolyphosphazene alkaline membrane, crosslinking membrane andblending membrane with polyethylene glycol200were preared andcharaterized. The main contents in this thesis are given as follows.1. The reaction condition of polydichlorophosphazene （PDCP） bysolution polymerization was optimized and P4MPP was synthesized. Theoptimum condition for PDCP is that the polymerization temperature is210°C and the reaction time is60min, then following a nucleophilicsubstitution with sodium p-cresol, PDCP was transformed to thecompound P4MPP. The Gel Permeation Chromatograph （GPC） testshowed that the molecular weight of P4MPP is up to105orders ofmagnitude. The thermogravimetric （TG） analysis indicated that P4MPP degrades at370°C.2. The bromination reaction condition of P4MPP by NBS regent wasoptimized to obtain bromination poly（4-methyl phenoxy）phosphazene（BP4MPP） in high yield. The optimum bromination time is2.5h, and thebromination percentage content of the product BP4MPP is up to85.23%.The GPC test showed that the molecular weight of BP4MPP is up to105orders of magnitude. The TG analysis indicated that BP4MPP degrades at150°C which belongs to the activity of the carbon-bromide key.3. Quaternary phosphonium poly（4-methyl phenoxy）phosphazene（QPP4MPP） was prepared via quaternary phosphonium reaction ofBP4MPP and triphenylphosphine. Then QPP4MPP membrane wasobtained by cast method. Finally, alkalization poly（4-methyl phenoxy）phosphazene （P4MPPOH） membrane was obtained through ion exchangereaction. The TG analysis showed that the pure polyphosphazene alkalinemembrane P4MPPOH begins to degrade at210°C. The tensile testindicated that the P4MPPOH membrane elongates1.5%when pressuredat20.511MPa stress. The solubility experiment showed that it is notsoluble in common organic solvents such as chloroform, N,N-dimethylformamide, tetrahydrofuran. The ionic conductivity test made it clear thatthe ionic conductivity of the P4MPPOH membrane increases with thetemperature increases and it reaches the highest of3.3mS cm^-1at90°C.The ionic exchange capacity of the P4MPPOH membrane is0.1876mmol g-1and the water uptake and swelling ratio are9.28%and4.16%respectively.4. The crosslinking polyphosphazene alkaline membrane doped withsodium polyethylene glycol （PEG）200and the blendingpolyphosphazene alkaline membrane doped with PEG were prepared aswell. The performance of the blending membrane in all aspects is betterthan the pure membrane and the crosslinking membrane. Particularly,when the doping amout of polyethylene glycol200is7%, theperformance of the blending membrane is the best. The ionic conductivityof the P4MPPOH&7%PEG blending membrane reaches4.2mS cm^-1andthe ionic exchange capacity is0.1903mmol g^-1. It degrades after210°Cand elongates3.25%when pressured at12.393MPa. The water uptakeand swelling ratio are11.91%and6.54%respectively.