Effects of phenyl-based pendent groups on helical conformation of poly(<Emphasis Type="Italic">N</Emphasis>-propargylamides) |
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Authors: | Xiaoqing Liu Bo Chen Kang Zhou Jianping Deng Wantai Yang |
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Affiliation: | (1) State Key Laboratory of Chemical Resource Engineering, Beijing, 100029, China;(2) College of Materials Science and Engineering, Beijing University of Chemical Technology, Beijing, 100029, China |
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Abstract: | 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 (M
n ≥ 10 000). 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. |
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