Microphase separation of copolymers is a key technique to produce polymer bulk materials or thin films with ordered nanostructures for applications in various research fields including nanotechnologies, electronic devices, among many others. Herein, we report water-assisted microphase separation of amphiphilic random copolymers bearing quaternary ammonium cations and hydrophobic alkyl or oleyl groups in the solid state and the thin films. We investigated the effects of sample preparation protocols and the hydrophobic pendants (a butyl group: C4 − octadecyl or oleyl group: C18), composition, and molecular weight of the copolymers on the microphase separation behavior. By annealing under humid conditions, the copolymers bearing alkyl groups longer than an octyl group (C8) formed sub-5 nm lamellar structures comprising cationic layers and hydrophobic layers. Water hardly remained in the resulting lamellar materials under ambient conditions. The domain spacing was controlled between 3.7 and 5.3 nm by tuning the length of the hydrophobic pendants and composition and was independent of the molecular weight and molecular weight distribution. The cationic random copolymers carrying amorphous hydrophobic pendants provided transparent or translucent polymer materials containing small lamellar structures. The random copolymers further formed multilayered lamellar thin films on silicon substrates by spin-coating the copolymer solutions, followed by a humid annealing process. The layered lamellae were directly observed as terrace structures with about 4–5 nm steps by atomic force microscopy.

Amphiphilic random and random block terpolymers bearing PEG chains, crystalline octadecyl groups, and amorphous oleyl groups were designed to control crystallization and microphase separation in the solid state.

Building cyclic units into amphiphilic copolymers is promising to produce ring-functionalized and self-assembled materials with unique properties. In this work, we developed versatile self-assembly systems of amphiphilic random cyclocopolymers in organic and aqueous media and the solid state to create nanoaggregates and microphase separation materials functionalized by cyclic oligo­(ethylene oxide) units. For this purpose, random cyclocopolymers consisting of hydrophilic oligo­(ethylene oxide) rings and hydrophobic alkyl groups were synthesized, into which the in-chain ring units were introduced via the cyclocopolymerization of divinyl monomers carrying oligo­(ethylene oxide) spacers. Typically, a cyclocopolyacrylamide bearing hydrophobic butyl groups self-assembled into nanoaggregates in chloroform and recognized a dibenzylammonium salt as a guest molecule with the in-chain rings, while the cyclocopolymer also formed thermoresponsive micelles in water and nanoaggregates and showed lower critical solution temperature-type solubility. Random cyclocopolymers carrying octadecyl groups afforded crystallization-driven microphase separation of their pendants in the solid state, giving sub-5 nm lamellar structure materials with the alternating layers of hydrophilic rings and crystalline octadecyl groups.