Ordered and Disordered Polymerized Ionic Liquid Block Copolymers: Morphology and Ionic Conductivity

We systematically studied the influence of temperature and relative humidity on morphology and ionic conductivity in polymerized ionic liquid block copolymers (PIL BCP). Poly(methyl methacrylate-$b$-1-[2-(methacryloyloxy)ethyl]-3-butylimidazolium-X$^{\mathrm{-}})$ block copolymers (X$^{\mathrm{-}} \quad =$ OH$^{\mathrm{-}}$, Br$^{\mathrm{-}})$ were characterized by SAXS, dynamical mechanical analysis, and electrochemical impedance spectroscopy. At 25 $^{\mathrm{^{\circ}}}$C, weak microphase separation was observed for the PIL BCP with $\phi _{\mathrm{PIL}} \quad =$ 0.38 and X$^{\mathrm{-}} \quad =$ OH$^{\mathrm{-}}$. Upon increasing the relative humidity to 90{\%}, this polymer exhibited an order-disorder transition (ODT). The ODT was further studied in the PIL BCPs with X$^{\mathrm{-}} \quad =$ OH$^{\mathrm{-}}$ and 0.11 \textless $\phi _{\mathrm{PIL}}$ \textless 0.38 over a range of temperatures and {\%}RH. In contrast, the PIL BCP with $\phi_{\mathrm{PIL}} \quad =$ 0.38 and X$^{\mathrm{-}} \quad =$ Br$^{\mathrm{-}}$ formed strongly microphase separated lamellae at all investigated T and {\%}RH. At elevated temperature and 90 {\%}RH, ionic conductivities of 30 and 6 mS/cm were observed for $\phi _{\mathrm{PIL}} \quad =$ 0.38 and X$^{\mathrm{-}} \quad =$ OH$^{\mathrm{-}}$ and Br$^{\mathrm{-}}$, respectively, surpassing the conductivities of the corresponding PIL homopolymer. By selecting the counterion and relative humidity, we significantly impact the morphology and ionic conductivity of these PIL block copolymers.