SINGLE-MOLECULE AFM STUDY OF ADHESIVE POLYMERS PREPARED BY COBALT-MEDIATED RADICAL POLYMERIZATION AND NITRONE-MEDIATED RADICAL COUPLING

Well-defined poly(vinyl acetate) (PVAc) chains prepared by CMRP (cobalt-mediated radical polymerization) were coupled using an alkyne-functional nitrone via NMRC (nitrone-mediated radical coupling).1 In all the cases, the coupling efficiencies were close to 90% or higher. The polymers mid-chain functionalized with an alkyne group were then reacted with azide-functionalized atomic force microscopy (AFM) tips via copper-catalyzed azide-alkyne cycloaddition (CuAAC). As a result, polymers having a double-branch architecture were linked to AFM tips via a short linker. The structure and the molecular parameters of the polymers were determined by NMR and GPC, whereas the ‘click’ step onto AFM tips was assessed by performing the same CuAAC reaction onto macroscopic surfaces and characterizing them by ATR FT-IR.

The adhesive properties of these double-branched polymers were studied by AFM single-molecule force spectroscopy. By performing approach-retraction cycles in solution upon a glass surface, the interaction between single PVAc chains and the surface was investigated. The effect of the double-branch architecture on the adhesion forces was under focus. Setting a residence time of the tip on the surface before retraction was found to have a beneficial influence on the adhesion forces. Signs of multiple interactions acting in parallel were detected in the experimental force-distance traces.