Preparing cyclic polymers at high concentrations via self-folding cyclization technique by adjusting the contents of hydrophilic units in linear precursors

Abstract

Cyclic polymers are a class of polymers that feature endless topology, and the synthesis of cyclic polymers has attracted the attention of many researchers. Herein, cyclic polymers were efficiently constructed by self-folding cyclization technique at high concentrations. Linear poly((oligo(ethylene glycol)acrylate)-co-(dodecyl acrylate)) (P(OEGA-co-DDA)) precursors with different ratios of hydrophilic and hydrophobic moieties were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization using a bifunctional chain transfer agent with two anthryl end groups. The amphiphilic linear precursors underwent the self-folding process to generate polymeric nanoparticles in water. By irradiating the aqueous solution of the nanoparticles with 365 nm UV light, cyclic polymers were synthesized successfully via coupling of anthryl groups. The effects of the ratios of hydrophilic and hydrophobic moieties in linear P(OEGA-co-DDA) copolymers and polymer concentration on the purity of the obtained cyclic polymers were explored in detail via1H nuclear magnetic resonance (1H NMR), dynamic light scattering (DLS), UV‒visible (vis) analysis, three-detection size exclusion chromatography (TD-SEC) and transmission electron microscopy (TEM). It was found that by adjusting the content of the hydrophilic segments in linear precursors, single chain polymeric nanoparticles (SCPNs) can be generated at high polymer concentrations. Therefore, cyclic polymers with high purity can be constructed efficiently. This method overcomes the limitation of traditional ring-closure method, which is typically conducted in highly dilute conditions, providing an efficient method for the scalable preparation of cyclic polymers.