Preparation Of Core/Shell Polymer Nanoparticles Based On Substituted Helical Polyacetylene

Five achiral N-propargylamide monomers with various phenyl-based substitutents, [HC=CCH2NHCOR, R for M1:C6H4CH3; M2:C6H4CH2CH3; M3:C6H4(CH2)2CH3; M4: C6H4(CH2)3CH3; M5:C6H4C(CH3)3], were synthesized and polymerized with a rhodium catalyst, (nbd)Rh+B-(C6H5)4 (nbd= 2,5-norbornadiene). The corresponding five homopolymers were obtained in high yields of 90-95%and with moderate molecular weights (Mn≥10000). All the polymers possessed high cis contents (≥95%). Poly(1)-poly(3) exhibited UV-vis absorption peaks at approx.350 nm, which indicates that the three polymers formed helical conformations, while no UV-vis absorption peaks could be observed in poly(4) and poly(5) in the wavelength range of 320-500 nm, demonstrating that these two polymers could not adopt helical structures under the examined conditions. To confirm the helical structures formed in poly(1)-poly(3), a chiral monomer, M6, was utilized to copolymerize with M2, which was used as the representative for M1-M3. M6 was utilized since its polymer could form stable helices under suited conditions. The resulting copolymers exhibited remarkable CD effects, however, the maximum wavelength in the copolymers varied remarkably, mainly depending on the composition of the copolymers. It is concluded that in the formation of ordered helical conformations, the substitutents of varied bulk led to different steric repulsion and varied synergic effects among the neighboring pendent groups.In order to explore the effects of solvents on the polymerization of propargylamide, polymerization of M7 was carried out with Rh catalyst in various solvents with different polarity, including toluene (C7H8), chloroform (CHCl3), tetrahydrofuran (THF), methylene dichloride (CH2Cl2), and dimethylformamide (DMF). The obtaining polymers can reach high yields. According to the CD and UV-vis spectroscopy, the polymers can adopt helical conformation and present optical activity in these five solvents, even in DMF with high polarity. With an increase in the molecular weight of polymers, the CD signals and UV-vis absorptions of the five polymers in the same solvents increased. As the polarity of solvents increased, the the CD signals and UV-vis absorptions of one polymer in the five solvents have a decrease.A novel methodology is reported about preparing a new class of core/shell nanoparticles. The nanoparticles consist of a unique core (composed of an optically active helical-substituted polyacetylene) and a shell (composed of a vinyl polymer) and thus exhibit optical activities. Such nanoparticles were synthesized by combining aqueous catalytic microemulsion polymerization and free radical polymerization in one specific system. The shell and core could be further cross-linked for improving the properties of particles by using multifunctionalmolecule. The investigations are of high importance not only in polymer chemistry due to the combination of catalytic polymerization and free radical polymerization in one system but also in materials due to the integration of "chirality" and "nano" concepts in one single material.