Morphological dependence on the addition of a soft middle block segment to rigid POSS-containing triblock copolymers for forming cylindrical nanostructures

A series of novel polyhedral oligomelic silsesquioxane (POSS)-containing triblock copolymers that self-assemble into hexagonally-packed cylinders of the POSS domain in a polystyrene (PS) matrix was developed in this study. POSS-containing diblock copolymers prefer to form lamellae as the aggregation of the rigid rods of the POSS-containing polymer chains results in a zero interfacial curvature. Cylindrical structures of the POSS-containing domain could not be obtained even when the volume fraction of the POSS-containing domain was reduced. Therefore, to obtain the cylindrical structures which are desirable for nanofabrication purposes, we designed a novel triblock copolymer with short polyisoprene (PI) middle blocks inserted between PS and poly(polyhedral oligomeric silsesquioxane methacrylate) (PMAPOSS) blocks. Differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) analyses suggested that the short PI block does not form a separate domain but is miscible with the PS and PMAPOSS blocks. This intermixing of the PI block has led to the development of a controlled interfacial region (CIR) between the two domains and a non-zero interfacial curvature required for forming cylinders.