Enhanced Block Copolymer Phase Separation Using Click Chemistry and Ionic Junctions
In addition to the traditional parameters of chi (χ) and degree of polymerization (N), we demonstrate that the segregation strength of a diblock copolymer can be increased by introduction of an ionic unit at the junction of the two blocks. Compared to neutral linking groups, the electrostatic interactions between counterions of adjacent domain junctions leads to increased enthalpy, segregation strength, and phase separation. As a result, the order disorder transition temperatures of block copolymers with a 1,2,3-triazolium ionic junction were observed to be significantly higher than the corresponding neutral block copolymers. To demonstrate the potential of block copolymers with ionic junctions for nanopatterning, block copolymers were prepared by click coupling of homopolymers and then used to fabricate well-defined sub-10 nm line features. We believe that the concept of improved thin-film assembly through the introduction of ionic junctions is a powerful tool for block copolymer lithography and complements chi (χ) and degree of polymerization (N) in the design of macromolecular systems with enhanced phase separation.