Molecular Conformations of Monodendron-Jacketed Polymers by Scanning Force Microscopy

• Published in: Macromolecules 1999-04, Vol.32 (8), p.2653-2660
• Main Authors: Prokhorova, Svetlana A, Sheiko, Sergei S, Ahn, C.-H, Percec, V, Möller, Martin
• Format: Article
• Language: English
• Subjects: Applied sciences; Exact sciences and technology; Organic polymers; Physicochemistry of polymers; Properties and characterization; Structure, morphology and analysis
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/ma981326j

Scanning force microscopy on monodendron-jacketed linear polystyrenes demonstrated unusual conformations and ordering depending on the branching density and interplay between intramolecular and surface interactions of the dendritic coat. Single molecules were visualized as wormlike cylinders, which could be twisted to plectonemic coils or aligned in nematic-like order on the substrate. The attained resolution enabled identification of chain-end stacking, hairpin folds and crossovers of individual macromolecules. The structure of the more densely branched 3,4,5-tris[3‘,4‘,5‘-tris(n-dodecan-1-yloxy)benzyloxy]benzyl was predominantly controlled by the intramolecular repulsion of the crowded dendron substituents which enforced an extended conformation of the molecular backbone. Formation of molecular monolayers was affected by wetting/dewetting events during casting, and the film structure did not depend on the substrate type. In contrast, the less crowded 3,4,5-tris[4-(n-tetradecan-1-yloxy)benzyloxy]benzoate (14-ABG-PS) was demonstrated to undergo conformational transitions upon drying and adsorption, as indicated by the observed built-up of torsional stress in the backbone. On mica, 14-ABG-PS formed a web of intertwined twisted cylinders. On graphite, lattice matching between the crystalline surface and the all-trans conformation of the alkyl side chains caused alignment of the macromolecules according to the 3-fold symmetry of highly oriented pyrolytic graphite. Subsequent annealing resulted in the formation of large domains of parallel aligned macromolecules.