Influence of Ionic Species on the Microphase Separation Behavior of PCL-b-PEO/Salt Hybrids

Abstract

The microphase separation behavior of the hybrids of poly(ε-caprolactone)-b-poly(ethylene oxide) (PCL-b-PEO) with different inorganic salts at various doping ratios (r) was studied by temperature-variable SAXS. It was observed that the salts could induce microphase separation to form ordered structure in the originally miscible melt of PCL-b-PEO. The effects of the metal ion and anion were correlated with the competitive interactions of PEO/salt and PCL/salt, which were characterized by FT-IR and DSC, respectively. It was found that at lower doping ratios the salts preferentially interacted with PEO. The larger association number of the metal ion and stronger association between PEO and salt led to a lower onset doping ratio for formation of ordered structure (r0). At higher doping ratios the salt interacted with PCL as well. When the metal ion exhibited a highly selective interaction toward PEO, a more ordered structure with a higher order–order transition temperature (TODT) tended to be formed. The anion in the salt also affected the interactions of PEO/salt and PCL/salt. Weaker Lewis basicity of the anion would result in a stronger interaction of PEO/salt and thus a lower r0. The results showed that the microphase separation behavior of the PCL-b-PEO/salt hybrids was sensitive to the competitive interactions of the salt with the PCL and PEO blocks.