Well-shaped poly(dimethylsiloxane)-based copolymer nanowires from spherical micelles via kinetic shape evolution

The formation of self-assembled arrays or superstructures from copolymers has attracted intense research interest. Herein, we propose a kinetic approach to form self-assembled nanowires using a PDMS-based block copolymer consisting of poly(dimethylsiloxane)-b-poly[2-(cinnamoyloxy)ethyl methacrylate] (PDMS-b-PCEMA). The copolymer was synthesized by using the macroinitiator PDMS-Br to initiate 2-(trimethylsiloxy)ethyl methacrylate (HEMA-TMS) via ATRP, followed by hydrolysis of the TMS group and gradual esterification with cinnamoyl chloride. PDMS-b-PCEMA presented core-shell spherical micelles in tetrahydrofuran, which transformed into nanowires within 5 days self-assembly via a typical kinetic shape evolution. The diameter of the assembled nanowires with a PCEMA inner core and PDMS shell was about 25-35 nm. The formation of these nanowires reflected a balance between the PDMS and PCEMA components: the PDMS segment was soluble enough to form a corona block, which was beneficial for the transformation of the micellar shape. Meanwhile, the PCEMA segment was able to control the diameter of the nanowire micelles but had no decisive effect on their formation. The effect of solvents on the self-assembled micelles indicated that nanowires were formed in tetrahydrofuran and dichloromethane, while core-shell micelles were formed in acetone. This was due to the different permittivities of these solvents. The nanowires were fixed by cross-linking the PCEMA group under UV irradiation, which enhanced their stability. We believe that this work provides a new strategy for the formation of nanowires and offers a guide for the diversified self-assembly of nanostructures from copolymers.