Impact of chain flexibility of copolymer gelators on performance of ion gel electrolytes for functional electrochemical devices

In this study, rationally designed random copolymers containing highly flexible, low glass transition temperature (T_g) segments are suggested as effective polymeric gelators for high-performance ion gel electrolytes. To this end, a series of poly(styrene-ran-butyl acrylate) copolymers (PS-r-PBAs) is prepared by a one-pot reversible additional-fragmentation chain transfer polymerization. Physically crosslinked ion gel electrolytes are produced by self-assembly when blended with ionic liquids of 1-butyl-3-methylimidazolium bis(trifluoromethyl sulfonyl)imide ([BMI][TFSI]). The properties of gels based on PS-r-PBAs and PS-ran-poly(methyl methacrylate)s (PS-r-PMMAs) are compared at similar molecular conditions. As a result, the effectiveness of the high chain flexibility of butyl acrylate is shown by higher ionic conductivity. The gels with PS-r-PBAs are further optimized in terms of the molecular characteristics of copolymers (e.g., the content of Sty and total molecular weight) and gel composition. The versatility of PS-r-PBA-containing gels as practical electrolyte platforms is demonstrated by preparing all-in-one type electrochromic devices, for which electrochromic ion gels are prepared by incorporating chromophores into the gels. To extend the functionality of the electrochromic devices, dot-shaped electrochromic gel arrays are fabricated for actively controllable smart windows that can reduce the window strike of birds.