Niya Ye,Yixin Xu,Dengji Zhang,Jingshuai Yang,Ronghuan He
We employed four radical inhibitors to investigate their influences on the degradation of poly (4-vinylbenzyl chloride-styrene) based anion exchange membranes (AEMs) in alkaline solutions. It is found that the presence of the radical inhibitors could effectively restrain the nucleophilic attack of hydroxide ions to the AEMs according to the conductivity measurements, especially the one p -ethyl phenol (PEP), which could significantly protect the AEMs against the attack. More evidences including water uptake, swelling ratio as well as FT-IR analysis further proved this phenomenon by comparison those properties of the membranes before and after the stability test in 8 M KOH at 80 °C for 24 h. According to the 1 H NMR spectra, the quaternary ammonium groups of the AEMs were mainly degraded into tertiary amines in the hot alkaline solutions; while in the presence of PEP, this degradation was restrained and the quaternary ammonium groups maintained by reaction with PEP. Fenton test results further indicated that high oxidative stability of the AEMs benefited from the presence of a small amount of PEP, which could reduce the generation of the oxidants. Thus an inhibition reaction mechanism of the radical inhibitors preventing the AEMs from alkaline degradation is proposed.
Chao He,Ke-Fei Han,Jing-Hua Yu,Hong Zhu,Zhong-Ming Wang
The introduction of sulfide units is a potential strategy to improve solubility and processibility of polybenzimidazole (PBI) polymer, as well as to enhance antioxidant capacity of corresponding membrane. In this paper, the novel S-PBI- x serial copolymers ( x denotes the percentage of sulfide-containing monomer) were prepared by a microwave-assisted tetracopolymerization with 3,3′,4,4′-tetraaminobiphenyl, 2,6-pyridinedicarboxylic acid, hexanedioic acid and the synthesized methyl 3-((2-methoxy-2-oxoethyl)thio)propanoate as copolymerized monomers in different proportion. The resultant copolymers were characterized by FT-IR, GPC and energy dispersive spectroscopy. These sulfide-containing copolymers exhibit much better solubility in aprotic solvents such as N,N-dimethylacetamide, N,N-dimethylformamide and dimethylsulfoxide than unmodified PBI. The oxidative stability of the membranes was studied by enhanced Fenton test (20% H 2 O 2 and 4 ppm Fe 2+ , 80 °C, refreshed every 3 h). Additionally, the oxidized membranes were further characterized by FT-IR, TGA, and tension test. The experimental results show that S-PBI-7% membrane suffers less than 5% weight loss after 24 h of treatment with enhanced Fenton reagent. Typically, after treated in enhanced Fenton reagent, the oxidized S-PBI-7% membrane still retains considerable thermal stability and mechanical strength. The anti-oxidative mechanism of the prepared membranes was discussed as well.
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