Synthesis and ion responsiveness of optically active polyacetylenes containing salicylidene Schiff-base moieties

Acetylenic monomers containing salicylidene Schiff-base groups (1a and 1b) as well as Schiff-base and hydroxy groups (1c) were synthesized and polymerized with [(nbd)RhCl]2/Et3N catalyst to afford the corresponding polymers 2a-c with high molecular weights (Mn = 2.6-7.2 × 105) in high yields (75-97%). Polarimetric, circular dichroism (CD), and UV-vis spectroscopic analyses indicated that the polymers formed helical structures with a predominantly one-handed screw sense. The addition of metal ions to salicylidene Schiff-base-containing polymers 2a and 2b produced insoluble polymer/metal complexes through ionic cross-linking as a result of salicylaldimine-metal ion complexation. Polymers 2b and 2c underwent a helix-coil transition upon the addition of HSO4−, whereas these polymers did not exhibit responsiveness to other anions, such as F−, Cl−, and Br−.