Rare-earth coordination catalysts

Also, divalent TiPh2 activated with [Al(Me)0]x appeared to be a catalyst for syndiospecific styrene polymerisation [71]. Even 5-TiCh or (Acac)3TiCl3, when activated with [Al(Me)0]x, could yield a mixture of isotactic and syndiotactic polystyrenes. Some other catalysts, such as rare-earth coordination catalysts, have been successfully used to obtain syndiotactic-rich polystyrenes [72],... 

Yang et al. examined rare earth coordination catalysts. The Nd(naph)3/ y4/(fBu)3 catalyst system was found to produce syndiotactic-rich polystyrene [8]. They proposed that the catalytically active species might be an ionic complex because the addition of CCI4 increased the catalytic activity. 

Yang, M., Cha, C., Shen, Z. Polymerization of styrene by rare earth coordination catalysts. Polytn. 22, 919-923 (1990). 

RARE EARTH COORDINATION CATALYSTS IN STEREOSPECIFIC POLYMERIZATION... 

Features in the polymerization of dienes, olefins, and acetylenes with rare earth Coordination catalysts... 

Active species of rare earth coordination catalysts References... 

In later work in the Changchun Institute of Applied Chemistry, the correlation between stereospecifidty, catalytic activity and catalyst composition, polymerization mechanism and kinetics with rare earth coordination catalysts, as well as the structure and physical properties of the raw and vulcanized rubbers obtained therewith, have been studied. The results of these investigations have been reviewed in several articles (Shen, 1980 Shen et al., 1980 The Fourth Laboratory, Changchun Institute of Applied Chemistry, 1974,1981 Ouyang et al., 1981 Ouyang, 1981 Ouyang et al., 1983). 

Meanwhile, Throckmorton (1969) reported the polymerization of butadiene with rare earth catalysts in 1%9. The Russians (Rafikov et al., 1976 Monakov et al., 1977a,b Berg et al., 1978) and the Itahans (Mazzei, 1980 Wang Fosong et al., 1981) are also engaged in diene polymerization with rare earth coordination catalysts. 

Since 1981 Shen and coworkers (Shen et al., 1982b, 1983 Shen and Farona, 1983a,b, 1984) have been extending the study of using rare earth coordination catalysts toward polymerization of acetylene, phenylacetylene and some terminal alkynes. Thus, a new area of usage of rare earth coordination catalysts has been opened. Using rare earth catalysts, acetylene can be polymerized at room temperature into polyacetylene film, with a cis content as high as 98%, with metallic sheen. 

The discovery of rare earth coordination catalysts in stereospecific polymerization not only contributes to the development of Ziegler-Natta catalysts and stereospecific polymerization from the usual d-orbital transition elements to... 

Table 1 summarizes the rare earth coordination catalysts developed. 

Polymerization of propylene has not been successful with rare earth coordination catalysts under mild conditions for quite a long time. Cai et al. (1984) reported that propylene can be polymerized by a supported neodymium catalyst NdClj L/MgCl2 at 60°C and 9 atm with catalytic activity of 1077 g PP/gNd. Cogrinding NdClj L/MgClj with AlClj raised the catalytic activity, but the isotacticity of the polymer is only about 30%. 

Polyacetylenes obtained by rare earth coordination catalysts are silvery grey films with a metallic luster which are not soluble in organic solvents or inorganic acids and bases. It is worth noting that the PA so obtained is comparatively stable and isomerizes only slowly when it is stored in air at room temperature. 

In order to have more insight into the characteristics of these catalyst systems, the kinetics and mechanism of polymerization of acetylene in rare earth coordination catalysts were investigated (Yu Luping et al., 1985a). It was shown that the initial rate of the reaction, R, is first order with respect to the overall concentration of catalyst and the pressure of acetylene in the system. The kinetic equation can be written as ... 

Fig. 3. The mechanism of acetylene polymerization by rare earth coordination catalysts.

In the present case, no matter what kind of catalytic system was chosen, the butadiene content in the copolymer is always greater than that in the feed. Values of the reactivity ratios (and their product) found with different catalysts are listed in table 20. Generally, if the reactivity ratio of Bd is greater than that of isoprene, the copolymerization process is assumed to be by a coordination anionic mechanism. Thus, rare earth coordination catalysts again exhibit a coordination-anionic mechanism in the polymerization of diene. 

Wang Shenlong et al. (1984) prepared a copolymer of ethylene and butadiene with rare earth coordination catalysts. Factors affecting the copolymerization reaction, such as the variation of the monomer ratio, aluminum alkyl, ligand and rare earth element, have been investigated. It was found that the catalytic activity of various ligands and rare earth elements in copolymerization have the following order ... 

RARE EARTH COORDINATION CATALYSTS monomer have been observed and the former predominates ... 

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