Direct Observation of Poly(macromonomer) by Scanning Tunneling Microscopy*1

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Abstract
Direct observation of a single molecule of poly(macromonomer) adsorbed on a highly oriented pyrolytic graphite was carried out by scanning tunneling microscopy (STM). The poly(macromonomer) studied is multibranched polystyrene possessing very dense polystyrene side chains of uniform molecular weight, which was prepared by polymerization of polystyrene macromonomers. It was revealed that the polystyrene side chains of the poly(macromonomer) extended from the main chain and were observed as an array of parallel lines on the graphite. The interval between the side chains was estimated as 0.42±0.03 nm. This value indicates that the main chain does not have an all-trans conformation but a TG+TG- conformation of the staggered model with alternate arrangement of the side chains, although the main chain is highly extended. We also observed an intramolecular structure, i.e., phenyl groups in the side chain. The distance between the two nearest-neighbor phenyl groups in the same side chain was observed as approximately 0.30 nm, indicating that each side chain is adsorbed on the graphite surface with strong intra- and intermolecular interactions. It was also confirmed by STM that the polymerization of macromonomers took place to form poly(macromonomer) in spite of the extremely high segment density.

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