SUMMARY: Stereospecific polymerization of monosubstituted acetylenes was successfully performed using a Rh complex, [Rh(norbornadiene)Cl] 2 , as a catalyst, and the resulting polyacetylenes were characterized in detail by 1 H NMR, ESR, laser Raman, diffuse reflective UV, and wide-angle X-ray diffraction. The Rh complex was found to yield selectively the cis-transoid isomer even at room temperature in high yields when alcohol or triethylamine was used as the solvent. Additionally, the resulting cis-polyacetylenes were found to form a pseudohexagonal, columnar self-assembly or superstructure. Further compression of the cis-polymers induced cis-trans isomerization even at room temperature under vacuum, breaking rotationally the cis-C2C bonds and, thus, giving p-radicals as the origin of magnetic properties.

KEY WORDSLong-Lived Propagating Species / Rhodium Complex Catalyst / m-Chlorophenylacetylene / In recent years there has been a growing interest in the polymerization of aromatic acetylenes using transition metal catalysts. Several investigations have been described in the literature, 1 -4 including the living polymerization of ortho substituted phenylacetylenes by Mo-based catalyst. In our preliminary experiments, the polymerization of chlorinated phenylacetylenes, for example, o-chlorophenylacetylene ( o-CPA), m-chlorophenylacetylene (m-CPA) and pchlorophenylacetylene (p-CPA) in the presence of Rh complex-TEA catalyst was examined. Among their monomers, m-CPA was readily polymerized to quantitative conversion and the polydispersity of the resultant polymer, Poly-(m-CPA) soluble into common solvents was rather narrow. Therefore, the polymerization of m-CPA was studied using three kinds of Rh-based catalysts, i.e., Rh-TEA

Stereoregular polymerization of (o-ethoxyphenyl)acetylenes (OEPA) was performed using a [Rh(norbornadiene)Cl]2 catalyst in the presence of triethylamine to give poly((o-ethoxyphenyl)acetylene) (POEPA) bearing a cis-transoid form under mild conditions. The polymer underwent isomerization from the predominant cis form to the trans form when compressed at 200 kg/cm2 at room temperature. The polymers, obtained before and after the compression, were characterized in detail using laser Raman, diffuse reflective UV, ESR, and X-ray diffraction. The data suggested that the isomerization of the resulting polymer from the cis-transoid to the trans-transoid form was induced to give rise to the conjugated trans-planar zigzag structures, where unpaired electrons are stabilized as mobile electrons called solitons. The formation of the soliton radicals was confirmed by the motional narrowing of the line width observed in the ESR spectra of the compressed polymer. The trans conjugation length, n, (CC) n generated by the compression was estimated as n = ca. 22−45 using UV and laser Raman. The studies show that the compression of the cis-transoid POEPA form is the preferred method to isomerize it to the trans-transoid form. The compressed polymer contains a higher degree of conjugation compared with that of the thermal isomerization of the pristine polymer.

Phenylacetylene and its homologues bearing methoxy or chloro groups in the para position of the phenyl ring were stereoregularly polymerized by Rh complex catalysts, e.g., [Rh (norbornadiene) Cl]2, in the presence of various solvents. The 1H‐NMR and UV study of the Rh complex showed that the activity of the Rh catalysts greatly depends upon not only the ligand in the Rh catalyst but also on the solvent used, e.g., polyphenylacetylene with a highly cis‐transoidal content was quantitatively obtained when norbornadiene was coordinated as the ligand, and triethylamine (TEA) was used as solvent, whereas tetrahydrofuran (THF) and benzene reduced the cis content. It was also found that the Rh catalyst as a dimer complex dissociates into the monomeric species not only when TEA was used but also when alcohol, benzene, and THF were used. The resulting monomeric species was considered as the important propagation species in this polymerization. The sharp line width observed in the 1H‐NMR spectrum of polyphenylacetylene and its homologues which were prepared in ethanol or TEA was interpreted by the narrow chemical shift distribution arising from the high cis content. © 1994 John Wiley & Sons, Inc.

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Stereoregular polymerization of (p-nitrophenyl)acetylene (pNPA) was performed using [Rh(norbornadiene)Cl]2 and [Rh(cyclooctadiene)Cl]2 catalysts to give poly((p-nitrophenyl)acetylene) (PpNPA), with a cis−transoid form under mild conditions. The polymer underwent isomerization from the predominant cis to trans form when compressed at 200 kg/cm2 at room temperature. The polymers, obtained before and after compression, were characterized using IR, CP MAS 13C NMR, ESR, and diffuse reflective UV methods. The data suggest that the isomerization of the resulting polymer from cis−transoid to trans−transoid form gives a conjugated trans planar zigzag structure. The trans conjugation lengths, n, in the polymer chain (CC) n after the compression were estimated as ca. 29 or 50, when polymers obtained with methanol or triethylamine as the polymerization solvents were used. The trans sequence length obtained by thermal treatment of the cis−transoid polymer was also found to have less conjugated sequences than that of the compressed polymer. It is concluded, therefore, that the compression of the predominant cis−transoid PpNPA form gives longer conjugated trans sequences compared with that of the thermal isomerization of the pristine polymer.

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