Globular Hydrophilic Poly(acrylate)s by an Arborescent Grafting-from Synthesis

Functional properties of macromolecules arise out of their chemical composition and their 3D conformation, exemplarily demonstrated by the secondary and tertiary structures of biomacromolecules. In synthetic macromolecules, precise introduction of branching and amphiphilicity are essential concepts to introduce shape-controlled functionality. Here, we report on the advancement of the concept of arborescent or graft-on-graft macromolecules from hydrophobic to hydrophilic polymers and the topologically controlled interfacial activity of such polymers. We synthesized hydrophilic arborescent polymers up to generation three (G3) in a grafting-from procedure. These are globular polymers with a high conformational flexibility, a feature otherwise found for biomacromolecules. Copper-wire catalyzed single electron transfer living radical polymerization (SET-LRP) of ethylene glycol methyl ether acrylate (EGMEA) and hydroxyethyl acrylate (HEA) allowed quantitative grafting initiation and end-group functionality. Degrees of polymerization of the grafts were adjusted around 25, and the total molecular weights varied from 35 × 103 g·mol–1 for G0 to a maximum of 3 × 106 g·mol–1 for G3 at polydispersities Đ ≤ 1.2. In agreement with the sizes determined by dynamic light scattering (DLS) in a tetrahydrofuran solution, dissipative particle dynamics (DPD) simulations demonstrated that the molecules approached a globular conformation with increasingly more flat density profiles. At the same time, the molecules preserved a high conformational flexibility. This unique combination contributed to a strong interfacial activity in toluene-in-water suspensions. The molecules spread at the liquid–liquid boundary and adopt a disc-like conformation. Interfacial activity and molecular spreading were demonstrated by spinning drop tensiometer measurements (SDT) and scanning force microscopy (SFM) imaging of single molecules.