Materials chemistry of chiral macromolecules. 2. Solid-state structures

Molecular organization in the solid state of a homologous series of chiral and achiral polymers was studied by electron microscopy and electron diffraction. All polymers of the series had periodic molecular backbones and some contained a stereocenter substituted by nitrile groups every 16 or 17 atoms along the chain. An aliphatic unit served as a spacer between aromatic units and was part of the repeats in all polymers. This spacer contained either an even or odd number of carbons in order to generate a preference for extended or nonextended conformers, respectively. Enantiomeric enrichment of chains resulted in the formation of crystals but diastereomeric chains with even spacer formed a phase of intermediate order and those with odd spacer formed an amorphous material. Enantiomerically enriched chains are also board-shaped and organize edge-to-edge, a feature definitely not observed in one of the two unsubstituted (achiral) homologous chains studied here. The global conformational traits of chains determined if extended-chain or folded-chain crystals formed.