Understanding Polymerization-Induced Nanostructural Transitions Using in situ Characterization Methods

Polymerization-induced structural transitions have been used to create nanostructured in a host of applications ranging from energy to separation technologies. Recently, our group has achieved order-order and disorder-order structural transitions by polymer grafting from linear block polymers mixed with monomer. In our approach, we are able to induce either a lamellar-to-hexagonally-packed cylinder (LAM-HEX) or a disordered-to-HEX transition via the polymerization of styrene, which initially acts as a neutral solvent for the lamellar-forming diblock copolymer, poly(styrene)-block-poly(butadiene) (PS-PBD). In situ small-angle X-ray scattering (SAXS) and rheological experiments during the polymerization process reveal a complex phase path in which we initially disorder the lamellar morphology at elevated temperatures. During the progression of the polymerization, the disordered phase transitions first to an ordered state, and then converts into the double gyroid phase. We are able to recover the HEX phase after polymerization when the sample is cooled to room temperature. 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.