Accessing block copolymers with independently modulated tacticities using sequential cationic-anionic polymerization...

Tacticity can have profound effects on the physical properties of polymers, such as self-assembly of block copolymers (BCPs). Despite its promise, previous reports on changing tacticity of BCPs have primarily focused on changing a single block or comparing fully isotactic to fully atactic copolymers. Herein, we report a platform to easily access fully atactic, fully isotactic, and mixed tacticity poly(vinyl ether)-block-poly(thiirane) BCPs. Isotacticity was independently accessed via stereoselective polymerization of vinyl ethers and by using enantiopure thiirane monomers, respectively. Thermal analyses of these materials were performed and semi-crystallinity was observed in aryl-containing isotactic blocks. For BCPs with alkyl side chains or atactic aryl side chains, fractionation on the basis of composition was performed to accelerate self-assembly studies. These fractionated BCPs were characterized via small-angle X-ray scattering (SAXS), where we observed hexagonally-packed cylinder or lamellar morphologies for some fractions. The development of this framework of selective tacticity modulation opens up facile access to diverse BCPs with varying thermal, solution-state, and bulk properties.