Chiral Microspheres Consisting Purely of Optically Active Helical Substituted Polyacetylene: The First Preparation via Precipitation Polymerization and Application in Enantioselective Crystallization

This article reports on a novel type of microspheres (similar to 720 nm in diameter) prepared via precipitation polymerization and constructed by optically active helical substituted polyacetylene (PSA). The microspheres were obtained in high yield (>80%), with regular morphology and narrow size distribution. PSA forming the microspheres was found to adopt helices with predominant one-handed screw sense, according to circular dichroism and UV-vis absorption spectroscopies and specific optical rotation measurements. The helical conformations of PSA endowed the microspheres thereof with considerable optical activity. The chiral microspheres feature in combining in one entity the advantages of both chiral polymers and the micrometer-sized particles in scale and spherical morphology and thus are expected to find some significant applications. This is well exemplified by successful induction of enantioselective crystallization with the chiral microspheres. Such chiral microspheres efficiently induced enantioselective crystallization of alanine enantiomers: (S)-PSA preferably induced L-alanine to form octahedral crystals while (R)-PSA toward D-alanine forming needle-like crystals, with a remarkably high ee (85%). This is the first precipitation polymerization of substituted acetylenes for preparing chiral polymeric microspheres. The present chiral microspheres represent a new type of advanced functional chiral materials.