Impact of Macromolecular Design on Self-assembly Properties of Block copolymers: Effect of Tunable Chain Flexibility and Chain Topology

The generation of well-ordered complex structures from constituent block copolymeric building blocks by the spontaneous process of self-assembly is useful in various technologies. The well-defined 3D structures are dictated by complex energetic interplays and their shape is controllable by both preparative conditions and macromolecular design. This dissertation work aims at exploring the effect of chain flexibility and chain topology design changes on phase behavior of block copolymers in solution. Further, we exploit the tunable flexibility of the semiflexible polymers in studying dispersion and controlling macroscale thermal properties in polymer nanocomposites.

The experimental design is based on two model systems: The first is based on polystyrene-b-poly1,3-cyclohexadiene (PS-b-PCHD). Here, the semiflexible nature of PCHD is tunable through alteration in the chain microstructure of the polymer backbone. As altered flexibility impacts the ability of chains to pack, which is shown to affect micelle morphology in solution. Further, we exploit the entropic contributions due to changes in chain configuration of PCHD (controlled through microstructure to control the dispersion of silica nanoparticles in matrices varying flexibility. Because we leave the monomer type unchanged, studying PCHD-based materials enables us to draw links between chain configuration and phase behavior. The second system is based on polystyrene-polyisoprene, (PS-PI), where multiple star copolymers were studied in a PI selective solvent. The study highlights how architecture and composition influence self-organization of the topologically-complex polymers in solution. The topological constraints introduced through architecture and composition were unable to induce any morphological changes, however design variation was successful in inducing changes in micelle size.

These studies help understand the self-assembly properties of semiflexible and topologically-complex systems and provide means to control micelle properties through macromolecular design. Additionally, the macromolecular design changes also provide an opportunity to control and enhance desired properties in polymer nanocomposites. Thus, the work conducted as a part of this dissertation is very valuable to understand design-structure-property relationships by providing insights into the physics principles operating at the nanometer length scale.