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 /Et 3 N catalyst to afford the corresponding polymers 2a – c with high molecular weights ( M n   =   2.6–7.2   ×   10 5 ) 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 HSO 4 − , whereas these polymers did not exhibit responsiveness to other anions, such as F − , Cl − , and Br − .