Polymers containing unsaturated N-heterocyclic cations (i.e., imidazolium) have been synthesized and investigated for various applications, including alkaline fuel cells and batteries. Recently, results have shown higher alkaline chemical stability for polymers bearing a saturated N-heterocyclic cation (pyrrolidinium) versus an unsaturated imidazolium cation. Additionally, several studies on small molecules have reported increasing stability with increasing saturated N-heterocyclic cation size and this was attributed to decreasing ring strain with increasing cation size. However, to date, few studies have systematically investigated polymers containing saturated N-heterocyclic cations, specifically N-heterocyclic cations with larger ring sizes (i.e., azepanium, azocanium, azonanium). In this study, styrene-based saturated N-heterocyclic cationic (SNHC) polymers with various covalent attached cations (methylpyrrolidinium, methylpiperidinium, methylazepanium) were successfully synthesized to investigate the influence of ring size/strain on the properties of SNHC polymers. Functionalization of poly(vinylbenzyl chloride) was employed to covalently attach cations onto polymer backbone, followed by anion exchange metathesis, resulting in polymers with bromide counter anions. Alkaline chemical stability, temperature and humidity dependent water uptake, and ion conductivity of these SNHC polymers were measured and will be reported in regards to the relationship with ring size/strain. This work provides a fundamental understanding of the ring size/strain effect in SNHC polymers and further introduces a promising chemistry for producing highly stable and ion conductive solid-state separators for alkaline fuel cells and batteries.

Saturated N-heterocyclic cationic polymers: Synthesis and stability

255th National Meeting (2018)

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