Polyacetylenes substituted polymers highly permeable

Typical functions of substituted poly acetylenes are based on their (i) high gas permeability and (ii) electronic and photonic properties. The former originates from the rigid main chain and bulky substituents. Though electrical insulators, substituted polyacetylenes are more or less conjugated polymers, and this feature has been utilized to develop their electronic and photonic functions such as photoconductivity, electrochromism, optical nonlinearity and ferromagnetism. 

Terminal alkynes substituted with chiral substituents have been polymerized by using a rhodium catalyst, [RhCl(NBD)]2 (NBD = norbomadiene) [6]. As shown in Scheme 3, polymerization of a chiral (carbamoyloxy)phenylacetylene 4 forms a cis-substituted polyacetylene 5. Due to the bulkiness of the substituents, these polymers show a helical conformation with no extended conjugation in the polymer chain. These materials are potentially useful as enantioselective permeable membranes to separate racemic amino acids and alcohols in water or in methanol. They can be also used as chiral stationary phase for enantioselective high-performance liquid chromatography (HPLC) analysis. 

Since polymers of substituted PA have good solubility and good air stability, they make good membranes. Even though substituted PA do not possess very high conductivity, some of them exhibit excellent gas and liquid permeability. These two factors combined imply that substituted polyacetylenes could potentially be used for the oxygen enrichment of air and the separation of ethanol-water mixtures [111]. 

Poly(DPA) is, thermally, the most stable substituted polyacetylene, but it is insoluble in any solvent, and hence it is impossible to fabricate a membrane from it by solution casting. In order to prepare this polymer membrane, desilylation of poly[l-phenyl-2-p-(trimethylsilyl)phenylacetylene] (PTMSDPA) membrane has been examined by use of trifluoroacetic acid as catalyst in hexane. The desilylation reaction proceeds to completion, as evidenced by IR spectroscopy and the anticipated weight decrease (eqn [a] in Scheme 4). As expected, the poly (DPA) membrane produced is insoluble in any solvent and possesses high thermal stability. This polymer shows fairly high gas permeability irrespective of the absence of any spherical substituent, as described below. The pinanylsilyl-containing poly(DPA) in eqn [b] is soluble, membrane-forming, and CD-... 

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