Ordering in Mixtures of a Triblock Copolymer with a Room Temperature Ionic Liquid

Abstract

Well-ordered block copolymer (BCP) morphologies are obtained by blending PEO−PPO−PEO triblock copolymer surfactants with the room temperature ionic liquid (IL) 1-butyl-3-methylimidazolium hexafluorophosphate. The selective association of the IL with the PEO blocks increases the segregation strength by raising the effective interaction parameter between the PEO and PPO blocks. Therefore, the copolymer/IL blends form well-ordered microdomains in the melt, whereas the neat copolymers are phase mixed. The IL is shown to interact with the PEO chains of the copolymers by a depression in the melting point of the PEO crystals with increasing IL concentration. Wide-angle X-ray diffraction and polarized optical microscopy also show a disruption of PEO crystallization in the copolymer/blends. Infrared spectroscopy indicates a favorable enthalpic interaction between the PEO blocks and the IL, which does not exist between PPO and the IL. Small-angle X-ray scattering confirms the enhanced ordering of the copolymers upon addition of the IL, the formation of well-ordered microdomains, and a change in the characteristic spacing with increasing IL concentration.