Article pubs.acs.org/Macromolecules
Chiral Microspheres Consisting Purely of Optically Active Helical Substituted Polyacetylene: The First Preparation via Precipitation Polymerization and Application in Enantioselective Crystallization Dongyue Zhang, Ci Song, Jianping Deng,* and Wantai Yang State Key Laboratory of Chemical Resource Engineering, College of Materials Science and Engineering, Beijing University of Chemical Technology, Beijing 100029, China S Supporting Information *
ABSTRACT: This article reports on a novel type of microspheres (∼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.
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INTRODUCTION The past decade witnessed large progress in the preparation of chiral materials, in particular micrometer- and submicrometersized chiral polymer particles. As a newly emerging type of advanced materials, polymeric chiral particles have aroused much attention recently.1,2 Such particles can be prepared via monomer polymerization3 or via self-assembly4−6 approaches. They have found significant applications in asymmetric catalysis,7−10 enantioselective crystallization,11 chiral resolution,12,13 etc. However, the chirality of nearly all the chiral polymer particles so far documented in the literature was exclusively contributed by small-molecular chiral entities. The chirality of polymers may be derived from small-molecule chiral configurations or macromolecular helicity as observed in optically active helical polymers.14−19 This unique group of polymers frequently demonstrates “chiral amplification” effects20,21 due to the ordered helical polymer backbones. Regretfully, no other chiral microspheres (micrometer- and submicrometer-sized) constructed purely by synthetic helical polymers have been reported up to date, apart from our earlier nanoparticles22 (
