Cationic Ring-Opening Polymerization-Induced Self-Assembly (CROPISA) of 2-Oxazolines: From Block Copolymers to One-Step Gradient Copolymer Nanoparticles

In recent years, polymerization-induced self-assembly (PISA) has emerged as a powerful method for the straightforward synthesis of polymer nanoparticles at high concentration. In this study, we describe for the first time the synthesis of poly(2-oxazoline) nanoparticles by dispersion cationic ring-opening polymerization-induced self-assembly (CROPISA) in n-dodecane. Specifically, a n-dodecane-soluble aliphatic poly(2-(3-ethylheptyl)-2-oxazoline) (PEHOx) block was chain-extended with poly(2-phenyl-2-oxazoline) (PPhOx). While the PhOx monomer is soluble in n-dodecane, its polymerization leads to n-dodecane-insoluble PPhOx, which leads to in situ self-assembly of the formed PEHOx-b-PPhOx copolymers. The polymerization kinetics and micellization upon second block formation were studied, and diverse nanoparticle dispersions were prepared, featuring varying block lengths and polymer concentrations, leading to dispersions with distinctive morphologies and physical properties. Finally, we developed a single-step protocol for the synthesis of polymer nanoparticles directly from monomers via gradient copolymerization CROPISA, which exploits the significantly greater reactivity of EHOx compared to that of PhOx during the statistical copolymerization of both monomers. Notably, this approach provides access to formulations with monomer compositions otherwise unattainable through the block copolymerization method. Given the synthetic versatility and application potential of poly(2-oxazolines), the developed CROPISA method can pave the way for advanced nanomaterials with favorable properties as demonstrated by using the obtained nanoparticles for stabilization of Pickering emulsions.