Control over structural dispersity within brushes generated by controlled radical polymerization

Constituted by a polymethacrylate (PMA) backbone and oligomeric ethylene glycol (OEG) side chain, POEGMA brushes find widespread application as functional coatings for various substrates, particularly in the design of biomaterials and biosensors. Tuning key properties, like lubricity and biopassivity, is essential in these applications. It has already been shown that properties of these polymer brushes strongly depend on several parameters like molecular weight, grafting density, and dispersity of the main polymer chain. Despite techniques for precise control over these variables, intrinsic polydispersity persists in POEGMA brushes due to the commercial OEGMA source featuring a broad distribution of macromonomers with varying OEG chain lengths. Therefore, the effect of the dispersity of the side chains on relevant interfacial properties of POEGMA-functionalized surfaces still has not been extensively elucidated. In this work, the macromonomer with m=8 ethylene glycol units in the side chain was isolated through flash silica chromatography of a commercial OEGMA (Mn ~ 500 g mol-1) featuring polydisperse OEG chains (m = 2-15). The corresponding brushes with either discrete or polydisperse side chains, P(OEG)8MA and P(OEG)pMA, respectively, were prepared via atom transfer radical polymerization from flat silicon substrates. Synthesized brushes were analyzed in terms of their physiochemical properties, through spectroscopic ellipsometry, quartz crystal microbalance, contact angle measurements and colloidal probe atomic force microscopy. Collectively, results suggest that POEGMA brushes with non-uniform lateral chains’ lengths exhibit reduced swelling, lower lubricity, and adhesive behavior compared to analogous brushes with uniform side chains. Side-chain heterogeneity therefore emerges as a promising new parameter for the design of functional materials with tailorable interfacial properties.