Reconstruction Of Block Copolymer Micelles To Ordered Nanopatterns Via Light-tunable H-bonding Association

Self-assembly of block-copolymer micelles has attracted increasing attentions. The recent achievements have showed fascinating potentials for applications in various fields, such as the energy storage, lithography and electronics. Controlling the orientation and long-range order of nanostructures comparable to those in atomic and molecular crystals is still challenging. Vast majority of recent studies focused on selective solvophobic interactions. Clearly, binding directionality is indispensable to achieve the orientation and long-range ordering of assembled nanostructures, and non-covalent dative bonds and hydrogen bonds have been demonstrated for directional self-assembly. These results shed light on long-range ordered reconstruction of block copolymer micelles through H-bonding.Based on comprehensive literature research, we present the reconstruction of block copolymer micelles into long-range ordered nanopatterns by virtue of a light-tunable Hbonding association. It is well known that oximes are easily accessible and ubiquitous in laboratory and large-scale production. A range of crystallographic results have revealed that H-bonding donors(-OH) of E-oximes are linked with nitrogen atoms(C=N) of adjacent molecules predominantly in a dimerization mode in solids. After photoisomerization under ultraviolet(UV) irradiation, hydrogen bonding converted outwardly into chain-like association(Z-type), leading to dramatic increase in a melting point of bezaldoxime solids from 35oC(E-type) to 130oC(Z-type) Inspired by this unique behavior, the transformation of oxime-based block copolymer spherical micelles into long-range ordered nanopatterns was thus attempted on various substances by adjusting E/Z-oxime ratio through photoisomerization.Poly(2-(4-formylphenoxy)ethyl acrylate)-block-poly(n-butyl acrylate)(PFPEA-bPnBA) was synthesized by reversible addition-fragmentation chain transfer(RAFT) polymerization under visible light irradiation at 25 oC. These reactions proceeded fast in a controlled manner and could be started/suspended immediately by turning on/off light, such that the chain lengths were controlled. Thus, oxime functionalized polymers were synthesized. Post functionalization into oxime-based PHMPEA and PHMPEA-b-PnBA was achieved via converting the aldehydes into the oxime derivatives through imine formation with hydroxylamine for further research.Photoisomerization provides a straightforward and versatile approach to convert the hydrogen-bonding association from inward dimerization(E-type oxime motifs, slightly desolvated in ethyl acetate) into outward inter-chain association(Z-type ones, highly desolvated in ethyl acetate). Thus improves the glass transition temperature in bulk and converts swollen micelles into compact spherical micelles in solution. The reconstruction of these micelles on various substrates has demonstrated that the phase transformation enables reconstruction of spherical micelles into mesoscopic sheets, nanorods, nanoworms, nanowires, networks, and eventually into long-range ordered and densely packed textilelike and lamellar nanopatterns to a macroscopic scale by adjusting E/Z-oxime ratio and solvent-evaporation rate.