| Abstract
| - A disk-shaped molecule, N-(5-sorbyl-pentyl)-N‘,N‘‘-di(n-octyl)benzene-1,3,5-tricarboxamide (1),has been synthesized and assembled into a columnar stack in cyclohexane. Using a photoinitiated process,we polymerized monomer 1 in its self-assembled state and analyzed the resulting poly-1. On cooling aboiling cyclohexane solution of 1, the molecules aggregate via amide hydrogen bonds, as supported bythe position of the N−H stretching band in FT-IR spectroscopy. Evidence of helical columnar stacking of1 in the aggregate is provided by an induced CD effect upon blending 1 with a chiral side-chain homologue3 in a so-called “sergeants and soldiers” experiment. The columnar assembly in cyclohexane waspolymerized by UV light (365 nm) irradiation in the presence of 2,2-dimethoxy-2-phenylacetophenone asradical photoinitiator. The polymerization occurs selectively to give 1,4-polymer with isolated trans CCbonds, as shown by FT-IR, and 1H and 13C NMR spectroscopy. Lack of polymerization of methyl sorbate(4) under identical conditions, and low incorporation of 4 in copolymerizations with 1 in cyclohexane, suggeststhat the polymerization preferentially occurs within the columnar assembly. Size exclusion chromatographyshows that the degree of polymerization (Xn) based on number average molecular weight is approximately65. Incorporation of small amounts of nonpolymerizable derivatives 2 and 3 into the columns has no effecton Xn and conversion. Molecular models show that the polymerizable sidearm of 1 is long enough to spanthe distance between the monomers in the chiral stack. Under the atomic force microscope (AFM), purifiedsamples of polymerized 1 displayed nanometer-sized fibrous morphologies with a high-axial-ratio (>150),uniform width (60 nm), and a thickness (1.0 nm) which corresponds to the width of the benzenetricarboxamide core of 1, whereas aggregates of nonpolymerized 1 yield a featureless image due to theirinstability.
|
