Sub 10-nm Self-Assembly of Mesogen-containing Diblock Macromonomers and their Graft-through Polymers

We explore the morphology and phase behavior of branched diblock macromonomers and their grafted-through polymers. A library of materials was synthesized based on a recently developed architecture, with each macromonomer in the library consisting of a polydimethylsiloxane (PDMS) homopolymer branch and a branch containing 1, 2, or 3 cyanobiphenyl (CB) mesogens. Each macromonomer was then polymerized to 3 different degrees of polymerization (N=10, 25, or 50). Due to the immiscibility of the two branches, the molecules self-assemble to form classically observed microphase-separated structures, including spheres, hexagonally packed cylinders, bicontinuous gyroid, or lamellae. We report the observation of well-ordered lamellae and cylinders with d-spacings as low as 6.1 and 8.0 nm, respectively. We find that the coil-branch-rod(s) structure leads to an asymmetric phase diagram. Other unique features of the samples in this library include highly birefringent textures observed by polarized optical microscopy and a distortion of microstructure for some samples due to crystallization. The small d-spacings and large grain sizes observed here highlight the versatility and potential utility of this molecular architecture for designing and engineering new functional materials.