Helical poly(phenylacetylene)s containing schiff-base and amino groups: Synthesis, secondary structures, and responsiveness to benzoic acid

Abstract

Novel acetylenic monomers containing Schiff-base and amino groups, (S)-N-(4-ethynylbenzylidene)-1-phenylethanamine (1a), (R)-N-(4-ethynylbenzylidene)-1-phenylethanamine (1b), N-(4-ethynylbenzylidene)-1-phenylethanamine (1c), (R)-N-(4-ethynylbenzyl)-1-phenylethanamine (1d), and (R)-N-(4-ethynylbenzyl)-1-phenylethanamine (1e) were synthesized and polymerized with [(nbd)RhCl]2/Et3N catalyst to afford the corresponding polymers 2a-e with moderate molecular weights (Mn = 9000–60,000) in high yields (85–97%). All the polymers were soluble in common organic solvents including toluene, CHCl3, CH2Cl2, THF, and DMF. Large optical rotations and strong CD signals demonstrated that 2a, 2b, 2d, and 2e take helical structures with a predominantly one-handed screw sense. The effects of solvents and temperature revealed that these polymers took dynamic helical structure based on the steric effect of side groups. The CD patterns of 2d and 2e containing free amino moieties were completely inverted by the addition of benzoic acid. Upon further addition of NaOH, the CD pattern returned to the original one, indicating the reversible conformational change of these polymers according to pH. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2013, 51, 5248–5256