Polyvalent hydrogen-bonding functionalization of ultrathin hyperbranched films on polyethylene and gold
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Hyperbranched poly(acrylic acid) and poly(N-isopropylacrylamide) grafts on gold and polyethylene films are good substrates for a new, mild hydrogen-bond-based grafting method. In this chemistry, a hydrogen-bond-donating or -accepting hyperbranched graft couples to a polymeric acceptor or donor in ethanol solution through multiple hydrogen-bonds. In contrast to plain surface-functionalized polyethylene films or to functional monolayers on gold, hyperbranched grafts are more capacious and more tenacious in this hydrogen-bond graft chemistry. Substantial amounts of polyacrylamide or poly(acrylic acid) reversibly bind to the hyperbranched graft based on IR spectroscopy, fluorescence spectroscopy, and ellipsometry. Fluorescence studies using dansyl-labeled soluble polymers that were hydrogen-bonded to hyperbranched grafts show that these hydrogen-bond assemblies are stable to prolonged extraction with protic and aprotic solvents. These interfacial hydrogen-bonded assemblies do not readily disassemble unless the hydrogen-bond donor is deprotonated with base.