Effect of Partial Hydrogenation on the Phase Behavior of Poly(isoprene-b-styrene-b-methyl methacrylate) Triblock Copolymers

We studied the effect of selective hydrogenation of the polyisoprene block in poly(isoprene-b-styrene-b-methyl methacrylate) (ISM) triblock copolymers on nanoscale network phase formation. The morphologies of the resulting poly((ethylene-alt-propylene)-b-styrene-b-methyl methacrylate) (EPSM) triblock copolymers and several EPSM copolymer/homopolymer blends were investigated using a combination of small-angle X-ray scattering and transmission electron microscopy, where well-ordered HEX, S-A, and Q(230) (network) nanostructures were identified. Variations in the nanoscale morphologies and phase boundaries between EPSM copolymers and their corresponding ISM precursors can be attributed to the differences in conformational asymmetry and block interactions. Of particular interest, the growth in the gyroid network region in the EPSM relative to the ISM is highlighted as the expansion of this region could further enable the creation of network-forming nanoporous membranes made from materials that are expected to demonstrate improved resistance against thermal and oxidative degradation.