Chain-Length-Dependent Hydrogen-Bonded Self-Assembly of Terminally Functionalized Discrete Polyketones.

Here, we report the synthesis and the chain-length-dependent self-assembling behaviors of discrete di-, tetra-, and hexaketones terminally functionalized with hydrogen-bonding carboxyl (, , and ) and 3-acylaminopyridine groups (, , and ). These polyketones were prepared by the coupling reactions of silylated analogues of 3,3-dimethylpentane-2,4-dione and -butyl 2,2-dimethyl-3-oxobutanoate and the subsequent hydrolysis or amidation with 3-aminopyridine. Single-crystal X-ray diffraction analysis revealed that and form helical assemblies in which the components are connected by the dimerization of terminal carboxyl groups, whereas the longer showed infinite hydrogen-bonded chains mediated by 1,4-dioxane used as a crystallization solvent. Pyridine-terminated exhibited a three-dimensional hydrogen-bonded network owing to multiple NH···N-(pyridine) hydrogen bonds in the solid state. generated a double-helix-like fiber structure in the crystalline state. Among the pyridine-terminated polyketones -, only showed gelation behavior in chloroform (100 mM concentration) at 25 °C. The scanning electron microscopy measurement of xerogel revealed the formation of rod-like structures with a thickness of approximately 0.5-3.5 μm. These results demonstrate that the precise control of the polyketone chain length can significantly alter hydrogen-bonded self-assembly in the solid state and in solution even with the same terminal structures.