Two new chiral helical poly(hydroxyl-containing phenylacetylene) membranes without the coexistence of any other chiral moieties were prepared in the following manner:  (1) synthesis and homo- or copolymerization of two new chiral pinanylsiloxy-containing phenylacetylenes, (2) preparation of self-supporting membranes from the (co)poly(chiral pinanylsiloxy-containing phenylacetylene)s by a solvent-casting technique, and (3) depinanylsilylation of the preformed polymer membranes in situ. Complete depinanylsilylation was successfully achieved by treating with trifluoroacetic acid. The resulting membranes exhibited circular dichroism despite the absence of the chiral substituents, a fact indicating that the main chains of the polymers retained their chiral helicity. This is the first method to synthesizing such chiral poly(phenylacetylene) membranes. Since the membranes maintained their self-supporting properties, we were able to use them as enantioselective separation membranes in the permeation of an aqueous solution of a racemate. As a result, the importance of the contribution of the chiral main chain on enantioselective permeation was directly confirmed for the first time. In addition, since some of the depinanylsilylated membranes were insoluble in organic solvents, we could use them as an separation membrane for a toluene solution of a racemate.

A novel phenylacetylene (1) having two hydroxyl groups and a chiral pinanyl group together with the other three related phenylacetylenes has been synthesized and (co)polymerized by using an achiral catalytic system. Among the four monomers, only 1 is suitable to the asymmetric-induced polymerization (AIP). Chiral amplification phenomenon is only observed in the copolymerization of 1 with an achiral phenylacetylene having two hydroxyl groups (3). The tight helical cis-cisoidal main chain formed by making intramolecular hydrogen bonds between the hydroxyl groups in the copoly(1/3) enhances the efficiency of chiral induction and as a result chiral amplification phenomenon is observed during the copolymerization.

An insoluble chiral membrane of one-handed helical multihydroxy poly(phenylacetylene) without the coexistence of any other chiral moieties has been synthesized by in situ complete removal of a one-handed helical poly(phenylacetylene) having multihydroxymethyl groups and chiral pinanyl groups in each polymeric unit in the membrane state. Although the enantiopermselectivity was decreased, the permeability increased four times by removing the chiral groups. In comparison with the corresponding poly(phenylacetylene) having no hydroxymethyl groups and chiral pinanyl groups, the loss of enantiopermselectivity was much lower. It is believed that the multihydroxy groups could maintain the main-chain chirality or enhanced interaction with permeant.

No abstract