Facile Synthesis of Hybrid Silica Nanoparticles Grafted with Helical Poly(phenyl isocyanide)s and Their Enantioselective Crystallization Ability

In this contribution, we report on the facile synthesis of hybrid silica nanoparticles grafted with helical poly(phenyl isocyanide)s via both grafting from and grafting to strategies. First, triethoxysilanyl functionalized alkyne-Pd(II) initiator was anchored onto the surface of bare silica nanoparticles through silanization coupling reaction. Polymerization of phenyl isocyanide using the Pd(II)-anchored silica nanoparticles lead to the formation of hybrid nanoparticles grafted with helical poly(phenyl isocyanide)s. The surface initiated polymerization was revealed to proceed in a living/controlled chain-growth manner, afforded the hybrid nanoparticles with controlled thickness. P-31 NMR analysis indicated the initiation efficiency of the surface-anchored Pd(II) initiators is very high, and almost quantitative. The grafting density was determined to be similar to 0.89 nm(2)/chain based on the thermal gravity analysis (TGA). Polymerization of optically active phenyl isocyanide bearing an L-alanine with a long decyl chain using the Pd(II)anchored silica nanoparticles formed chiral hybrid nanoparticles grafted with helical poly(phenyl isocyanide) arms in preferred handedness. Second, the hybrid silica nanoparticles were prepared via grafting to strategy. Well-defined triethoxysilanyl terminated poly(phenyl isocyanide) was prepared in controlled manners. The polymer was grafted to the surface of bare silica nanoparticles via the silanization coupling reaction, afforded hybrid silica nanoparticles grafted with helical poly(phenyl isocyanide). TGA indicates the grafting density is similar to 0.76 nm(2)/chain. Taking advantage of this synthetic method, left-handed helical poly(phenyl isocyanide) was grafted to the surface of silica nanoparticles, generated chiral hybrid silica nanoparticles with high optical activity. Such chiral nanoparticle exhibited good performance in enantioselective crystallization of racemic Boc-alanine. The enantiomeric excess (ee) of the induced crystal is up to 95%.