Small-Angle X-Ray Scattering Studies of Block Copolymer Nano-Objects: Formation of Ordered Phases in Concentrated Solution During Polymerization-Induced Self-Assembly

We report that polymerization-induced self-assembly (PISA) can be used to prepare lyotropic phases comprising diblock copolymer nano-objects in non-polar media. RAFT dispersion polymerization of benzyl methacrylate (BzMA) at 90 degrees C using a trithiocarbonate-capped hydrogenated polybutadiene (PhBD) steric stabilizer block in n-dodecane produces either spheres or worms that exhibit long-range order at 40 % w/w solids. NMR studies enable calculation of instantaneous copolymer compositions for each phase during the BzMA polymerization. As the PBzMA chains grow longer when targeting PhBD80-PBzMA(40), time-resolved small-angle X-ray scattering reveals intermediate body-centered cubic (BCC) and hexagonally close-packed (HCP) sphere phases prior to formation of a final hexagonal cylinder phase (HEX). The HEX phase is lost on serial dilution and the aligned cylinders eventually form disordered flexible worms. The HEX phase undergoes an order-disorder transition on heating to 150 degrees C and a pure HCP phase forms on cooling to 20 degrees C.

Automated summary

Polymerization-induced self-assembly (PISA) is used to prepare lyotropic phases with diblock copolymer nano-objects in non-polar media. Through NMR and X-ray scattering studies, the copolymer compositions and phase transitions during benzyl methacrylate polymerization are revealed. The hexagonal cylinder phase undergoes an order-disorder transition upon heating to 150 degrees C, forming a pure hexagonally close-packed (HCP) phase upon cooling to 20 degrees C.