Abstract
We synthesized anion exchange polymers by a reaction of chloromethylated poly(2,6-dimethyl-1,4-phenylene)oxide (PPO) with strongly basic 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD). TBD contains secondary and tertiary amine groups in the guanidine portion. To favor the functionalization with the secondary amine, TBD was activated with butyl lithium. The yield of amine formation via the reaction of the benzyl chloride moiety with TBD was 85%. Furthermore, we prepared polymers with quaternary ammonium groups by the reaction of PPO-TBD with CH3I. The synthesis pathways and ionomer structure were investigated by NMR spectroscopy. The thermal decomposition of both ionomers, studied by thermogravimetry, started above 200 °C, corresponding to the loss of the basic group. The ion exchange capacities, water uptake and volumetric swelling are also reported. The “intrinsic” anion conductivity of PPO-TBD due to the dissociation of grafted TBD was in the order of 1 mS/cm (Cl form). The quaternized ionomer (PPO-TBD-Me) showed an even larger ionic conductivity, above 10 mS/cm at 80 °C in fully humidified conditions.
Highlights
The development of anion exchange membranes (AEMs) for electrochemical devices, such as fuel cells, represents an important challenge for many scientists [1,2,3,4,5,6]
To enhance its nucleophilic properties and to drive the reaction towards the formation of the formation of the tertiary amine, TBD was activated with butyl lithium (BuLi)
The tertiary amine, TBD was activated with BuLi
Summary
The development of anion exchange membranes (AEMs) for electrochemical devices, such as fuel cells, represents an important challenge for many scientists [1,2,3,4,5,6]. The main hindrances for their widespread application are low stability in alkaline conditions, poor hydrophilic/hydrophobic domain separation, the high water content needed to favor the dissociation of the ion pairs, and carbonatation issues that decrease the conductivity, just to mention a few [7,8,9,10,11,12]. These challenges seem very difficult to address, but the benefits of using AEMs justify the efforts. This concept is explored in this work and the properties of PPO-TBD are compared with those of the more classical quaternized PPO-TBD-Me obtained by the methylation of PPO-TBD
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