(298c) Self Assembly of Rod-Coil Block Copolymers and Homopolymers

The self-assembly of block copolymers provides an attractive means to control morphology and access a variety of nanostructured phases. Functional polymers such as helical proteins and semiconducting polymers frequently do not follow traditional block copolymer phase diagrams due to their rigid rod-like shape. The self-assembly of rod-coil diblock copolymers is controlled not only by the Flory-Huggins interaction between the blocks but also by the tendency of the rod segments to form anisotropic liquid-crystalline phases such as nematic and/or layered smectic phases. The interplay between microphase separation and liquid crystallinity leads to phase behavior that is distinctly different from classical coil-coil diblock copolymers. We recently demonstrated the self-assembly of a series of monodisperse rod-coil block copolymers in the weak segregation limit. This model polymer system self-assembles into lamellar, nematic, and isotropic phases with changing coil volume fraction and temperature.

Swelling the rod-coil block copolymer with homopolymer provides an alternative way to modify the morphology without additional synthesis. Due to the conformational contrast in the rod and coil, incorporation of homopolymer into the self-assembly process is expected to differ significantly from more traditional block copolymer structures. In fact, molecular weight matched rod-like homopolymers interdigitate with the rod-blocks within their respective lamellae. As a result of the interdigitation, the coil blocks must rearrange to occupy more interfacial area. This results in an unprecedented decrease in domain spacing with increasing rod homopolymer. Conversely when coil homopolymers are incorporated, they are locally solubilized within the coil microdomain resulting in an increase of domain spacing with increasing coil homopolymer. In this talk, we will discuss the self-assembly process of rod-coil block copolymers and blends as well as discuss the unusual stability of the lamellar phase in this system which allows it to persist even with large amounts of homopolymer incorporated.