A homologous series of polymerized ionic liquid (PIL) homopolymers and polystyrene-block-PIL block copolymers derived from [4-vinylbenzyl(alkyl)imidazolium]X (X = Cl, BF4, PF6, and bis(trifluorosulfonimide) (TFSI)) were synthesized by post- polymerization modification of poly(4-vinylbenyl chloride) with an alkylimidazole followed by salt metathesis. Homopolymers having BF4, PF6, and TFSI counterions were generally quite hydrophobic and exhibited temperature-dependent conductivities that correlate with their glass transition temperatures (Tg), wherein higher conductivities are observed for polymers that exhibit lower Tg’s. Polymers containing a chloride counterion were very hydrophilic and exhibited a conductivity that depends sensitively on relative humidity. The temperature-dependent ionic conductivities of hydrophobic polystyrene-block-PIL diblock copolymers were also measured as a function of ionic block content and morphology. In the context of these results, criteria for the design of highly conductive polymerized ionic liquids will be discussed.
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