1 research outputs found
Proton Conduction in Tröger’s Base-Linked Poly(crown ether)s
Exactly 50 years
ago, the ground-breaking discovery of dibenzo[18]Âcrown-6 (DB18C6)
by Charles Pedersen led to the use of DB18C6 as a receptor in supramolecular
chemistry and a host in host–guest chemistry. We have demonstrated
proton conductivity in Tröger’s base-linked polymers
through hydrogen-bonded networks formed from adsorbed water molecules
on the oxygen atoms of DB18C6 under humid conditions. Tröger’s
base-linked polymersî—¸polyÂ(TBL-DB18C6)-<i>t</i> and
polyÂ(TBL-DB18C6)-<i>c</i>î—¸synthesized by the in situ
alkylation and cyclization of either <i>trans</i>- or <i>cis</i>-diÂ(aminobenzo) [18]Âcrown-6 at room temperature have
been isolated as high-molecular-weight polymers. The macromolecular
structures of the isomeric polyÂ(TBL-DB18C6)Âs have been established
by spectroscopic techniques and size-exclusion chromatography. The
excellent solubility of these polymers in chloroform allows the formation
of freestanding membranes, which are thermally stable and also show
stability under aqueous conditions. The hydrophilic nature of the
DB18C6 building blocks in the polymer facilitates retention of water
as confirmed by water vapor adsorption isotherms, which show a 23
wt % water uptake. The adsorbed water is retained even after reducing
the relative humidity to 25%. The proton conductivity of polyÂ(TBL-DB18C6)-<i>t</i>, which is found to be 1.4 × 10<sup>–4</sup> mS cm<sup>–1</sup> in a humid environment, arises from the
hydrogen bonding and the associated proton-hopping mechanism, as supported
by a modeling study. In addition to proton conductivity, the Tröger’s
base-linked polymers reported here promise a wide range of applications
where the sub-nanometer-sized cavities of the crown ethers and the
robust film-forming ability are the governing factors in dictating
their properties