Synthesis of Heterografted Amphiphilic Cyclic Polymers via the Self-Folding Cyclization Technique and Their Application as Oil-in-Water Emulsion Stabilizers

Heterografted amphiphilic cyclic homopolymers were prepared by the self-folding cyclization technique. The reversible addition–fragmentation chain transfer (RAFT) polymerization of amphiphilic N,N′-disubstituted acrylamide with oligo(ethylene glycol) (OEG) and octyl groups (OEGOAM) was performed to afford linear POEGOAM homopolymers with two terminal anthryl groups. After self-folding in water, single-chain polymeric nanoparticles (SCPNs) were produced from the linear precursors via hydrophobic interaction. By irradiating the aqueous solution of SCPNs with 365 nm UV light, heterografted amphiphilic cyclic polymers were synthesized via intramolecular coupling of terminal anthryl groups. Due to the presence of hydrophobic alkyl and hydrophilic OEG side chains, both cyclic and linear POEGOAM homopolymers can be employed as emulsifiers to stabilize oil-in-water emulsions. Compared with the emulsion stabilized by linear POEGOAM, that using cyclic POEGOAM as the emulsifier exhibited higher long-term and high-temperature stabilities. The result could be attributed to the more compact conformation of cyclic polymers compared to linear polymers, which can provide higher stability of the newly created oil–water interface. This work not only enriches the monomer scope of the self-folding cyclization technique but also expands the application fields of cyclic polymers, as well as providing a novel insight for the design of efficient emulsifiers.