Marta Pacovská

Polybenzimidazole-supported [Rh(cod)Cl]2 complex: Effective catalyst for the polymerization of substituted acetylenes

The first heterogeneous catalyst which affords polymerization of substituted acetylenes into readily available high molecular weight polymers is reported. The catalyst (Rh/PBI) has been prepared by supporting di-mu-chloro-bis(eta4-cycloocta-1,5-diene)dirhodium(I), [Rh(cod)Cl]2, on commercial polybenzimidazole (PBI) porous beads by means of a simple quantitative adsorption from THF solution, and tested in polymerization of phenylacetylene, 4-fluorophenylacetylene, and 4-pentylphenylacetylene. The polymer molecules formed were found to be released from the Rh/PBI to surrounding solution during the polymerization performed in THF. Formation of high molecular weight ((M)w values up to 325,000) polymers in prevailing cis-transoid configuration has been observed with all monomers. In a comparison with free [Rh(cod)Cl]2 used as the homogeneous catalyst, the Rh/PBI can be used repeatedly, exhibits somewhat lower polymerization activity but almost no oligomerization activity, and provides polymers of higher molecular weight.

Poly(p-iodophenylacetylene): synthesis, characterization, polymer stability and photoelectrical properties

Abstract New functional acetylene, 1-ethynyl-4-iodobenzene, ( p -iodophenylacetylene) was prepared, characterized (i.r., n.m.r., u.v. and mass spectra) and transformed into high-molecular-weight polymers. Various WOCl 4 -based and MoCl 5 -based catalysts were used in the polymerization, the former leading to the red soluble and the latter to dark red insoluble poly( p -iodophenylacetylene) (PIPA), respectively. Both types of PIPA are non-crystalline and they differ in the configurational structure which, however, could not be assigned with certainty. A too high molecular weight and/or cross-linking is suggested as a reason of insolubility of PIPA prepared on Mo-based catalysts. The soluble PIPA was found to degrade autoxidatively in tetrahydrofuran solution at room temperature obeying the kinetic laws of polymer random degradation. The determined value of the rate constant of degradation, 2.6 × 10 −6 min −1 , is slightly higher than that found for unsubstituted poly(phenylacetylene) (PPA), under the same conditions. PIPA was found to possess a higher photo-conductivity than PPA at low and moderate electric fields. The Onsager model offers an adequate explanation for the measured dependence of the photogeneration efficiency of the applied electric field assuming the Gaussian distribution of the radii of charge-transfer states.

Polymerization of 4-(ferrocenylethynyl)phenylacetylene with transition metal catalysts

A new conjugated polymer carrying organometallic pendant groups, poly[4-(ferrocenylethynyl)phenylacetylene], has been prepared. [Rh(nbd)(OCH 3 )] 2 as a catalyst (nbd = norbornadiene) provides a mixture of an insoluble polymer (yield 71%) free of C≡CH groups and soluble oligomers (yield 22%, MW ca. 1100). WOCl 4 /2Me 4 Sn as a catalyst provides almost exclusively a polymer (yield 60%, M w = 32. 10 3 ) containing a small amount of C≡CH groups that is soluble in aromatic and low-polarity solvents. Its solubility, however, decreases upon storage in the solid state, probably due to a subsequent crosslinking. The 13 C NMR, IR, UV-vis and Raman spectra of the monomer and polymers are reported.

Pure WCl4-catalyst for polymerization of norbornene and monosubstituted acetylenes

Abstract A suspension of commercial WCl 4 initiates rapid polymerization of norbornene and norbornadiene under mild conditions. If norbornenyl acetate is used as a substrate, WCl 4 is dissolved and homogeneous polymerization occurs. In both cases polymers ( M w = about 80 000 ), the structure of which corresponds to the ring-opening metathesis mode of polymerization, were prepared. WCl 4 has also been found to polymerize monosubstituted acetylenes (benzene, 50°C). Poly( t -butylacetylene) of M w = 600 000 , poly(phenylacetylene) of M w = 200 000 and poly(1-hexyne) of M w = 14 000 were prepared in high yields. When WCl 4 was dissolved in the reaction with oxygen-containing compounds (e.g. methyl acetate, acetylacetone, acetophenone) before substrate addition, catalyst activity increased significantly. WCl 4 in 1,4-dioxane was found to be a very active system for phenylacetylene polymerization; it polymerizes this monomer at the monomer-to-catalyst mole ratio equal to 1000 providing polymer of M w = 400 000 .

Polymerizations Catalyzed with Rhodium Complexes

In the last decade, rhodium complexes are increasingly used as catalysts for a preparation of specialty polymers of diverse functionality, since a use of them brings about important advantages. Rh-catalysts (i) show unusually high tolerance to the reaction surroundings as well as to functional groups of reactants and products, (ii) they often show a precise control of the configurational structure of formed macromolecules (particularly those of polyvinylenes), (iii) they can be transformed to the living polymerization systems, (iv) they can be anchored on various inorganic and organic supports to give effective heterogeneous catalysts, and (v) they can catalyze reactions in the ionic liquid systems. Rhodium complexes are prevailingly used for a preparation of stereoregular (head-to-tail, cis-transoid) polymers of monosubstituted acetylenes, molecules of which easily adopt the helical conformation in the solid state, some of them even in solutions (e.g., molecules of poly(propiolate)s). In addition to it, Rh-complexes are nowadays used as catalysts of (i) atom transfer radical polymerization, (ii) polymerization of arylallenes taking place exclusively via 2,3-addition mode and copolymerization of allenes with carbon monooxide to give alternating copolymers, (iii) cross-dehydrocoupling polymerization of dihydrosilanes and bis(hydrosilane)s with diols, disilanols and dithiols, (iv) silylative coupling polymerization of bis(vinylsilane)s, (v) hydrosilylative addition copolymerization of bis(silane)s and diethynyl monomers, and (vi) ring-opening polymerization of silaferrocenophanes and 1,3-disilacyclobutanes. In spite of a high synthesis potential, a practical application of these expensive catalysts in a medium-to-large scale production of polymers depends on successful solving of questions related to their effective and reliable recycling.

Mesoporous Molecular Sieves Immobilized Catalysts for Polymerization of Phenylacetylene and Its Derivatives

Substituted polyvinylenes, polymers with conjugated polyene main chains, attract attention because of their unique properties implicating applications in electronics and optics [1] (electro- and photoconductivity, electro- and photoluminescence, optic non-linearity). So far, these polymers have been prepared almost exclusively by homogeneously catalyzed polymerization of corresponding substituted acetylenes with transition metal catalysts (most frequently compounds of W, Mo, Rh and Pd) [2, 3, 4]. However, catalyst residues in polymers may undesirably affect the polymer properties (especially those essential for their applications) and polymer purification (e.g. by repeated polymer precipitation) leads often to the decrease of molecular weight and changes in microstructure resulting from polymer degradation [5,6]. Therefore, new polymerization procedures minimizing the content of catalyst residues in the resulting polymers can be of important advantage.