Synthesis of Chiral Helical Poly(hydroxyl-containing phenylacetylene) Membranes by in-Situ Depinanylsilylation and Their Enantioselective Permeabilities

Abstract

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.

Transformation from preformed racemic helical poly(phenylacetylene)s to the enantioenriched helical polymers by chiral solvation, followed by removal of the chiral solvents

“…At this stage, the enantiopurity of the preferential helical sense is not clear, although the CD signal intensity of poly(5) in enantiopure PEA was comparable to that of poly(phenylacetylene)s bearing chiral pendant groups at the paraposition. 19,[48][49][50] However, this method is an attractive synthetic method for optically active helical polymers, as is the HSSP method, because the method does not require a chiral moiety in the monomer, thus increasing the flexibility for monomer design. For example, poly(5) has a TEMPO moiety that is a stable radical often used in magnetic and redox materials.…”

“…We have already succeeded in using the above methods to obtain poly(phenylacetylene)s with an induced kinetically stabilized helical bias. [15][16][17][18][19] Another approach is the use of external chiral stimuliinduced or chiral field-induced transformation from a racemic helical or achiral polymer to an enantioenriched helical polymer. In this approach, the chiral helical bias has often been induced by strong interactions such as acid-base interactions [20][21][22][23][24][25] and host-guest interactions [26][27][28][29][30][31] between a chiral molecule and a polymer.…”

Synthesis of a series of soluble main-chain chiral nonracemic poly(alkyl-aryl ketone)

“…Optical rotation was measured on a Rudolph Autopol III polarimeter and a JASCO-J-720 circular dichroism spectroscopy. 1 H NMR spectra were measured with a Bruker AM 250 (250 MHz) spectrometer. 13 C NMR spectra were recorded at 62.9 MHz on a Brucker AM 250 spectrometer.…”

“…The mixture was filtered and recrystallized from methylene chloridebenzene (1:1 mixture) to give the desired product (3.8 g, yield 89.5%). 1 …”

“…Main-chain chiral polymers are of great interest because of their important applications in chiral separation and recognition [1][2][3][4]. In order to achieve such goals materials must be stable and possess functional groups.…”