Pressure-Induced Cis to Trans Isomerization of Poly(o-methoxyphenylacetylene) Polymerized by Rh Complex Catalyst. A Raman, X-ray, and ESR Study

Precise synthesis of monosubstituted polyacetylenes using Rh complex catalysts. Control of solid structure and π-conjugation length

“…Therefore we concluded that 6 c and 6 f as well as other PAP polymers examined, have pseudohexagonal packing structures at room temperature [19][20] . Similar columnar polymers have been reported, e. g., poly(di-n-alkylsiloxane) 39) , poly(dialkylphosphazene) 40) and poly(o-methoxyethynylbenzene) 14) . The dependencies of the columnar diameters on the n-alkyl chain length, n = 3 -14, for the 6 a -l polymers were measured (Fig.…”

“…The line width of the ESR spectra of polymer 1 e showed no motional narrowing, even when the polymer was cooled from room temperature to 77 K, as reported for the case of 2 a 23) and 1 d polymers 14) polymerized with the Rh complex catalyst. This suggests that the radical spins generated during the polymerization and/or after the polymerization are stabilized in the cis-transoid form where the unpaired electrons can not move around along the main chain because of the restricted cis-conjugated chain 14,15,21,23) . It appears that the polymer chains which are packed in the hexagonal column may be helical chains which stabilize the columnar structure.…”

“…1 550 cm -1 was assigned to the naphthalene ring, overlapped with the cis-C2C bond in the cis-transoid. The large peak at 1 330 cm -1 was assigned to the C1C bond, coupled with the C1H bond in the cis-polymer, which is characteristic of aromatic polyacetylene having the cis-form as previously reported 14,23) . The Raman spectra of the PENAP-W polymer (2 b-W) prepared with the WCl 6 catalyst in toluene at 0 8C and 40 8C, respectively, were observed ( Fig.…”

“…Therefore, cyclohexanol, when used as the solvent, may induce a coagulation of the cis polyacetylene chains, giving rise to the columnar structure via a self-organization. This process may involve many radical spins which are stabilized in the cis main-chain as immobile unpaired electrons, as previously reported 14,15,23) . This suggests that, in the hexagonal solid state, the distribution of the radical spins is not homogeneous but heterogeneous.…”

“…However, except for the precise control of the molecular weight and its dispersity, there has been no clear and unequivocal assignment (Scheme 1) of the geometry and/ or regularity of the resulting polymers regarding the C2C bond in the main chain of the polymer, including few stereospecific polymerizations of cis-and/or transmonosubstituted polyacetylenes (i), copolymerization (ii), isomerization (iii) of cis-to-trans geometrical isomer with its mechanism (iv), generation of p-conjugated radicals as solitons through the rotational scission of the cisdouble-bond, and the role of the radical in the conductivity and/or magnetism of the polymer (v). In this report, we describe the stereospecific polymerization to yield selectively the cis-form using the [Rh(norbornadiene)Cl] 2 ([Rh(NBD)Cl] 2 ) catalyst [12][13][14][15][16][17][18] , leading to a control method of molecular orientation and/or spin order in solid polymers, i. e., the formation of pseudohexagonal structures [19][20][21] , aggregation of the radical spins as a source of magnetism [20][21] , pressure-induced cis-trans isomerization [14][15][16] , and generation of the p-radical through rotational scission of the cis-double-bonds (Scheme 1).…”