Salt-induced microphase separation in poly(ε-caprolactone)-b-poly(ethylene oxide) block copolymer

In the present work, a poly(ε-caprolactone)-b-poly(ethylene oxide) (PCL-b-PEO) block copolymer was doped with LiClO4 at various salt concentrations. The morphology of the hybrids was characterized with time-resolved small-angle X-ray scattering (SAXS). It is observed that LiClO4 can induce microphase separation of the miscible PCL-b-PEO in the melt. With increase in doping ratio, the morphology of the hybrids changes from cylinder into lamella. The order-disorder transition temperature (TODT) and domain spacing increase with doping ratio in the low salt concentration range, but decrease at higher salt concentrations. FT-IR, UV and DSC results show that LiClO4 preferentially interacts with PEO at low doping ratios, but also associates with PCL at high doping ratios. The effective Flory-Huggins interaction parameters (χeff) for the hybrids were calculated. It is found that at low salt concentrations the χeff increases linearly with doping ratio due to selective interaction between PEO and LiCLO4, but the competitive interaction of LiClO4 with PCL and PEO at high salt concentration can lead to decrease of χeff.