Synthesis of chiral helical poly(hydroxyl-containing phenylacetylene) membranes by in-situ depinanylsilylation and their enantioselective permeabilities

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.