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 NbCl 5 -, TaCl 5 -, or MoCl 5 -based catalysts to give high molecular weight polymers in good yields. Poly( 1 ) and poly( 2 ) 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( 2 ) 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( 2 ), 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( 2 ), and poly( 3 ) exhibited characteristic properties as gas-permeable and optical resolution membranes.