Aqueous solution behaviour of novel water-soluble amphiphilic copolymers with elevated hydrophobic unit content†
A series of water-soluble statistical copolymers poly(OEGMA-stat-styrene) and block copolymers poly(OEGMA-stat-styrene)-b-PDMAPMA have been synthesized via RAFT polymerization. Despite the polymers having a relatively high styrene content they are readily soluble in water, capable of forming transparent solutions at room temperature without resort to conventional solvent-exchange methods. 1H DOSY NMR, dynamic light scattering, transmission electron microscopy and atomic force microscopy indicate that the copolymers containing high styrene content formed nanoaggregates less than 15 nm in diameter. The self-assembly behaviour of the copolymers is significantly affected by copolymer composition. Chain extension of poly(OEGMA-stat-styrene) with a hydrophilic DMAPMA block resulted in formation of larger aggregates; higher contents of OEGMA reduced the aggregate size. 1H NMR in D2O reveals reduced molecular mobility of styrene segments within the core of the block copolymer aggregates compared with the statistical copolymers. However, measurements of the dynamic surface tension of the copolymers at the air–water interface demonstrate the high surface activity of the polymers and that the aggregates are highly dynamic in nature. All of the copolymers are able to form stable foams after agitation of aqueous solutions. The study not only provides a detailed understanding of the limits of incorporation of hydrophobic monomers into aqueous-soluble block copolymers, and how this affects chain dynamics, but also introduces a method for preparing water-dissolvable dynamic aggregates of sizes less than 15 nm. The dynamic nature of the polymers and the relatively high hydrophobic group content makes them promising materials for a number of nanotechnology applications.