Polymerization-Induced Morphology Transitions in Diblock Copolymer/Monomer Blends

In situ polymerization within confined spaces to either fix or template desired structures has found uses in numerous applications, but the process typically destroys the original structure. Here, we present on the polymerization-induced nanostructural evolution of diblock copolymer/monomer blends containing a lamellar-forming diblock copolymer, poly(styrene)-block-poly(1,2butadiene) (PS-1,2PBD) and styrene as the monomer. At high PS-1,2PBD volume fractions (φ_PS-1,2PBD > 40%), we are able to access lamellar morphologies, and at decreased volume fractions (φ_PS-1,2PBD ≤ 40%), we achieve a disordered morphology. On polymerization of the styrene within the blends, we are able to induce either a lamellar-to-hexagonal or a disorder-to-hexagonal transition. Interestingly, the order-order and disorder-order transitions occur via an unexpected mechanism in which the polymerized styrene monomer grafts from the pendent vinyl groups on the 1,2PBD. The polymerization of styrene leads to an increase in the overall molecular weight and the PS volume fraction of the PS-1,2PBD copolymer, driving the phase transitions. The work presented here highlights how the in situ process of converting standard linear diblock copolymers to block polymer bottlebrushes drives interesting morphology transitions.