Hierarchically structured bicontinuous polymeric microemulsions

We recently described the synthesis and phase behavior of a new type of CECEC-P multiblock copolymer composed of glassy poly(cyclohexylethylene) (C), semicrystalline poly(ethylene) (E), and elastomeric poly(ethylene-alt-propylene) (P) with symmetric (equal volume) CECEC and P sequences (G. Fleury and F. S. Bates, Macromolecules, 2009, 42, 3598-3610). Here we report the formation and characterization of a multicontinuous structure based on the blending of CEC triblock copolymer and P homopolymer with such a hexablock copolymer along the 50: 50 (CEC/P) isopleth. These materials produce a sequence of phases that are correlated with the volume fraction of CECEC-P as evidenced by SAXS and TEM measurements. A percolating bicontinuous mesostructure was identified at volume fractions of hexablock copolymer, f_CECEC-P = 0.10 and 0.125, within the composition range known to result in a bicontinuous morphology in A-B/A/B systems. A solid product was formed by cooling the initially homogeneous ternary mixture from above the melting temperature of the E blocks to room temperature. Crystallization of E leads to microphase separation of C and E and simultaneous ejection of P from CEC (and CECEC) at a larger length scale. The mechanical properties of these materials are inferior to what is anticipated based on pure CEC triblock copolymer, attributable to the low molecular weight and irregular structure of the C/E region sequences. Nevertheless, this study establishes a procedure for producing bicontinuous yet structurally asymmetric materials based on the microemulsion process and extends the concept of a microemulsion to multiblock copolymers.