Directed self-assembly (DSA) is a promising approach for extending conventional lithographic techniques by being able to print features with critical dimensions under 10 nm. The most widely studied block copolymer system is polystyrene-block-poly(methyl methacrylate) (PS--PMMA). This system is well understood in terms of its synthesis, properties, and performance in DSA. However, PS--PMMA also has a number of limitations that impact on its performance and hence scope of application. The primary limitation is the low Flory-Huggins polymer-polymer interaction parameter (), which limits the size of features that can be printed. Another issue with block copolymers in general is that specific molecular weights need to be synthesized to achieve desired morphologies and feature sizes. Here we explore blending ionic liquid (IL) additives with PS--PMMA to increase the parameter. ILs have a number of useful properties that include negligible vapor pressure, tunable solvent strength, thermal stability, and chemical stability. The blends of PS--PMMA with an IL selective for the PMMA block allowed the resolution of the block copolymer to be improved. Depending on the amount of additive, it is also possible to tune the domain size and the morphology of the systems. These findings may expand the scope of PS--PMMA for DSA.