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Download fileThermoresponsive Dendronized Poly(phenylacetylene)s Showing Tunable Helicity
journal contribution
posted on 04.11.2019, 12:34 authored by Fang Wang, Congcong Zhou, Kun Liu, Jiatao Yan, Wen Li, Toshio Masuda, Afang ZhangSwitching the macromolecular helicity
of poly(phenylacetylene)s (PPAs) through external achiral stimuli
provides convenient possibilities in designing smart chiral materials.
Herein, a series of PPAs carrying dendritic oligoethylene glycol (OEG)
pendants were synthesized with different linkages between the backbone
and dendron pendants, including benzamide (PPA-AC), inverted acylamide
(PPA-AM), diamide (PPA-dAM), benzoate (PPA-ES), and benzyl ester (PPA-OEG).
The periphery of the OEG dendrons is capped with either an ethoxy
(PPA-ACe) or a methoxy group (PPA-ACm) to afford the PPAs with different
overall hydrophilicity. These dendronized PPAs inherit unprecedented
thermoresponsiveness from the dendritic OEGs and show characteristic
thermally induced phase transitions with cloud points (Tcps) in the range 30–54 °C. Hydrogen bonding
interactions between neighboring repeating units were found to play
a key role in transferring chirality from pendants to polymer backbone.
Dependent on the linkages, these PPAs behave differently about helix–helix
transitions driven by the thermally induced collapse of the pendanted
OEG dendrons. Interestingly, dendronized homopolymer with methoxy
terminals (PPA-ACm) shows radial amphiphilicity in aqueous solutions,
which renders the polymer a different chiroptical property. For comparison,
chiroptical properties of these polymers were also investigated in
organic solvents. Furthermore, coordination with Ba2+ was
found to mediate the chiroptical properties of these dendronized PPAs
in aqueous solutions, which can be surprisingly shielded by OEG dendrons
below their Tcps.