Synthesis And Characterization Of Helical Polyacetylene Derivatives Containing Schiff-base Groups

The design and synthesis of optically active polyacetylene and its derivatives has become one hot area of new functional materials research, due to their unique optical and electrical properties. The introduction of functional Schiff-base group into the side chain of polyacetylene as a chiral auxiliary can afford functional helical polymer materials with strong optical activity and metal ion coordination ability, which will find promising applications in the field of assymetric catalysis, molecular recognition, enantioseperation and so forth. In this thesis, we have successfully synthesized a series of novel polyacetylenes containing Schiff-base groups and further studied their secondary structures and optical activities:(1) Novel acetylenic monomers containing Schiff-base and amino groups,(S)-N-(4-ethynylbenzylidene)-1-phenylethanamine(1a),(R)-N-(4-ethynylbenzylidene)-1-pheny lethanamine(lb),N-(4-ethynylbenzylidene)-1-phenylethanamine(lc),(R)-N-(4-ethynylbenzyl)-1-phenylethanamine (1d), and (S)-N-(4-ethynylbenzyl)-1-phenylethanamine (le)were synthesized and polymerized with [(nbd)RhCl]2/Et3N catalyst to afford the corresponding polymers2a-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 that2a,2b,2d, and2e take helical structures with a predominantly one-handed screwsense. 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 of2d and2e 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.(2) Novel optically active acetylenic monomers containing Schiff-base and hydroxyl groups,(R)-4-ethynyl-2-((1-phenylethylimino)methyl)phenol(1f),(S)-4-ethynyl-2-((2-hydroxy-1-phenylethylimino)methyl)phenol (1g),(S)-N-(4-Ethynylbenzylidene)-2-Phenylglycinol (1h) were synthesized and polymerized with [(nbd)RhCl]2/Et3N to afford the corresponding polymers2f-h with moderate molecular weights (Mn=1.5×7.0×105) in high yields (75-96%). Large optical rotations and strong CD intensities demonstrated that2f-h take helical main chains with a predominantly single-handed screw sense. The solvents and temperature dependence indicated that these polymers took dynamic helical structures based on the steric effect of side groups. The CD patterns of2h containing Schiff-base moities and free hydroxyl groups were gradually induced by the addition of hydrogen sulfate suggesting conformational change of2h according to hydroxyl sulfate. We further studied complexations between polymer2a,2e,2f-h and various metal ions with different valence and different particle sizes. Complex of polymer2e and copper ion(II), complex of2e and iron ions(III), complexes of polymer2f and polymer2g and metal ions above were successfully obtained, while polymer2a and2h cannot coordinate with the metal ions mentioned above. All of the complexes were insoluble in common organic solvents, including CH3OH, CH2Cl2, CH3Cl3, THF, and DMF. The structures of these complexes were investigated by IR spectra.