Self-Coacervation of Oligo(ethylene glycol) and Oligo(2-ethyl-2-oxazoline)-Based Double Hydrophilic Brush Block Copolymers in Aqueous Solution.

Coacervates are a highly relevant class of structures formed via liquid-liquid phase separation and new coacervate-forming polymers are highly sought after. Here, the formation of simple coacervate droplets from a double hydrophilic block copolymer (DHBC) with the combination of poly(oligo ethylene glycol methacrylate) (POEGMA) and poly(oligo 2-ethyl-2-oxazoline methacrylate) (POEtOx) without the use of external triggers or charges is shown. At a high concentration of 25 wt.%, the DHBC forms coacervate droplets with sizes in the low micrometre range. The droplets have relatively high stability over a long period of time with only minor coalescence observed after 4 weeks. At low concentrations, no coacervation is observed. Furthermore, copolymers of the monomers also do not show coacervation clearly indicating that the DHBC architecture is required to form the desired structures. The addition of guest polymers and biomacromolecules at low concentrations shows a specific partitioning behaviour with a preference for the polymer or the aqueous phase. At high guest concentrations, enrichment in the aqueous phase is observed, in line with common water-in-water (w/w) emulsions. These findings constitute a new direction for coacervate systems that are of interest for biotechnology, synthetic cell environment mimics and drug delivery.