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.
Particles constructed by chiral polymers (defined as PCPs) have emerged as a rapidly expanding research field in recent years because of their potentially wide-ranging applications in asymmetric catalysis, enantioselective crystallization, enantioselective release, amongst many others. The particles show considerable optical activity, due to the chirality of the corresponding polymers from which the particles are derived. This review article presents an overview on PCPs with emphasis on our group's recent achievements in the preparation of PCPs derived from optically active helical polymers and their applications. PCPs can be prepared via emulsion polymerization, precipitation polymerization, and suspension polymerization by starting from monomers. Emulsification of preformed chiral polymers and self-assembly approaches also can lead to PCPs. Chiral polymer-based core/shell particles, hollow particles, and magnetic particles are also covered because of their remarkable properties and significant potential applications.
Cross-linked microspheres consisting of optically active helical substituted polyacetylenes are reported. For preparing the microspheres, substituted polyacetylene copolymers with pendent polymerizable CC bonds are first prepared and then used as macromonomers to copolymerize with acrylates via suspension polymerization, providing cross-linked microspheres. The helical polymer segments render the microspheres with optical activity, whereas the acrylate-based polymers afford the swelling property. CD and UV-vis spectra demonstrate the optical activity of the microspheres. The microspheres preferably adsorb (R)-(+)-1-phenylethylamine, (R)-(+)-N-benzyl-1-phenylethylamine, and Boc-D-alanine, whereas released Boc-L-alanine rather more rapidly than its enantiomer.
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