Colloidal and bulk nanostructured materials fabricated via polymerization-induced structural transitions have been used in a host of applications ranging from biomedical to energy technologies. In the previous studies that explore polymerization-induced structural transitions, the starting reagents, such as macro chain-transfer agent (macro-CTA), monomer, and solvent, are initially well solubilized, creating a homogenous mixture. During the macro-CTA chain-extension process, the growing polymer becomes incompatible with the initial polymer segment and/or the solvent, leading to the formation of nanoscale domains. Our group has recently achieved order-order structural transitions by polymer grafting from block polymers that exhibit nanostructured morphologies before polymerization. In our approach, we are able to induce a lamellar-to-hexagonally-packed cylinder transition via the polymerization of styrene, which initially acts as a neutral solvent for the lamellar-forming diblock copolymer, poly(styrene)-block-poly(1,2 butadiene) (PS-1,2PBD). Furthermore, in situ small-angle X-ray scattering (SAXS) experiments during the polymerization process reveal a complex phase path in which the double gyroid phase is an intermediate morphology between the lamellar and hexagonally-packed cylinder phases. The lamellar-to-hexagonally-packed cylinder order-order transition occurs via a PS grafting mechanism in which PS chains are grafted to the 1,2PBD block. The PS grafting leads to an increase in the overall molecular weight and in the PS volume fraction of the PS-1,2PBD copolymer, driving the morphology transitions. The work presented here highlights how the chemical process of converting standard linear diblock copolymers to grafted-block polymers drives interesting and controllable morphology transitions.

Nanostructural transitions driven via in situ polymer grafting in diblock copolymer/monomer blends

256th National Meeting (2018)

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