Synthesis and properties of polymers from disubstituted acetylenes with chiral pinanyl groups

Disubstituted acetylenes with chiral pinanyl groups, (-)-1-{4-[dimethyl(10-pinanyl)silyl]phenyl)-2-phenylacetylene (1), (-)-1-{3-[dimethyl(10-pinanyl)silyl]phenyl}-2-phenylacetylene(2), (-)-1-{4-[dimethyl(10-pinanyl)silyl]phenyl}-1-propyne (3), and (-)-1-chloro-2-(4-[dimethyl( 10-pinanyl)silyl]phenyl)acetylene (4), polymerized with NbCl5-, TaCl5-, or MoCl5-based catalysts to give high molecular weight polymers in good yields. Poly(1) and poly(a) showed intense circular dichroism (CD) effects in the UV-vis region and large optical rotations, which suggests that these polymers exist in helical conformations with an excess of one-handed screw sense. No significant decrease in the magnitude of CD effects of poly(1) and poly(a) with increasing temperature indicated the relatively high stability of their helical conformations. On the other hand, the intensities of CDs of poly(3) and poly(4) were approximately 1/10 those of poly(1) and poly(a), which means that introduction of two aromatic side groups into the repeating unit is favorable for the induction of helical conformation to disubstituted acetylene polymers. The free-standing membranes of poly(1), poly(a), and poly(3) exhibited characteristic properties as gas-permeable and optical resolution membranes.