High-conductivity electrolyte gate dielectrics based on poly(styrene--methyl methacrylate)/ionic liquid

We report self-assembly of a statistical copolymer poly(styrene- co -methyl methacrylate) (P(S- co -MMA)) containing ionic liquid (IL)-philic methyl methacrylate (MMA) and IL-phobic styrene (S) repeating units in IL for fabrication of electrolyte-gated organic transistors. P(S- co -MMA)s with high MMA contents were synthesized by copolymerization of styrene and MMA via a reversible addition-fragmentation chain transfer (RAFT) process, and their behavior in 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([EMI][TFSI]) was investigated. While dynamic light scattering analysis showed formation of a micellar solution at low concentration, the elastic modulus of the viscoelastic solution increased significantly more than the loss modulus at high concentration. Small angle X-ray scattering analysis suggested ill-defined phase separation between PS-rich segments and PS-lean segments swollen in [EMI][TFSI]. The resulting P(S- co -MMA)/[EMI][TFSI] mixture exhibited increased ionic conductivity compared to the PS- b -PMMA- b -PS block polymer gel, as well as superior device performance in transistor gating experiments. Self-assembly of a statistical copolymer in an ionic liquid renders mechanical integrity and ionic conductivity suitable for electrolyte-gated transistors.