Polymerization of Diolefins

First patented by S. Horn (B. F. Goodrich), coordination polymerization of diolefins has yielded several industrially important products, as indicated by the approximate data below (Table II). 

4-polyisoprene (TiCVAlR3) (roughly equivalent to natural rubber from Hevea tree) 100 240 500 700 

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An influence by optically active groups bound to the transition metals on the complexation of the monomers with the same atoms might probably explain also the asymmetric polymerization of diolefins (95). 

For instance, in the polymerization of 1.3-pentadiene in the presence of a catalyst prepared from optically active titanium alcoholates and diethylaluminum monochloride, the diolefin might give a complex with a titanium atom before the polymerization (92) the steric structure of the complexed pentadiene molecule might be determined by the optically active alkoxy groups still bound to the titanium atom. However, the case of. the polymerization of diolefins is much more complex than the case of the polymerization of vinyl monomers owing to the possible... 

Further investigations are necessary to clarify the mechanism of stereoregulation in the polymerization of olefins and diolefins probably the stereoelective polymerization of vinyl monomers and the asymmetric polymerization of diolefinic compounds will give further interesting contributions to the future progresses in this field. 

Some of the alkylhydroperoxides, e.g. cumylhydroperoxide, are used for the polymerization of diolefin (butadiene) with comonomers (e.g. styrene) at low temperatures (5-20 °C). 

Catalytic conversions were experimentally studied in Russia toward the end of the nineteenth century, and especially in the twentieth century, and regularities were empirically established in a number of cases. The work of A. M. Butlerov (1878) on polymerization of olefins with sulfuric acid and boron trifluoride, hydration of acetylene to acetaldehyde over mercury salts by M. G. Kucherov (1881) and a number of catalytic reactions described by V. N. Ipatieff beginning with the turn of the century (139b) are widely known examples. S. V. Lebedev studied hydrogenation of olefins and polymerization of diolefins during the period 1908-13. Soon after World War I he developed a process for the conversion of ethanol to butadiene which is commercially used in Russia. This process has been cited as the first example of commercial application of a double catalyst. Lebedev also developed a method for the polymerization of butadiene to synthetic rubber over sodium as a catalyst. Other Russian chemists (I. A. Kondakov I. Ostromyslenskif) were previously or simultaneously active in rubber synthesis. Lebedev s students are now continuing research on catalytic formation of dienes. 

Medvedev has reported work on the kinetics of polymerization of diolefins and other compounds, as influenced by the number of free radicals in the reaction (230). In the polymerization of styrene, two chain reactions are thought to take place the reaction of free radicals with oxygen leads to oxidation, and the reaction with styrene to polymerization (231). 

The importance of the electrophilic character of the cation in organo-alkali compounds has been discussed by Morton (793,194) for a variety of reactions. Roha (195) reviewed the polymerization of diolefins with emphasis on the electrophilic metal component of the catalyst. In essence, this review willattempt to treat coordination polymerization with a wide variety of organometallic catalysts in a similar manner irrespective of the initiation and propagation mechanisms. The discussion will be restricted to the polymerization of olefins, vinyl monomers and diolefins, although it is evident that coordinated anionic and cationic mechanisms apply equally well to alkyl metal catalyzed polymerizations of polar monomers such as aldehydes and ketones. 

The type of alkylaluminum compound has only a secondary influence on structure in the polymerization of diolefins in contrast to its strong effect on the structure of polypropylene. An exception is AlEtCb, which, apparently in connection with its cationogenic character, with j3-TiCl3 induces polymerization to trans-1,4 polybutadiene and, even without transition metal compound, leads to formation of cyclized polyisoprene. Incidentally, this indicates that poly-butadiene is much more stable towards cyclization than polyisoprene. 

Some of the applications of the organometallic compounds of lanthanides are as catalysts for (i) stereo specific polymerization of diolefins and in particular to obtain high yields of 1,4-ci.v-polybutadiene and 1,4-cw-polyisoprene and copolymer of the two monomers. The order of effectiveness of the rare earths as catalysts is Nd > Ce, Pr < Sm, Eu. The nature of halogen of the Lewis acid affecting the catalytic activity is in the order Br > Cl > I > F. Detailed work on the activity of cerium octanoate-AlR3-halide showed stereo specificity with cerium as the primary regulator. Cerium is thought to form jr-allyl or 7r-crotyl complexes with butadiene. 

Table 6. Classification of morphological changes in polymerization of diolefinic monomers23,61)...

Quite recently, Nakanishi et al. have reported an example of crystalline-state dimerization for which the product matrix is essentially of single-crystal character63. On the other hand, it may be assumed that any solid-state polymerization of diolefinic crystals, which results in an amorphous product, gives a pseudomorph. 

Recent investigations have shown lithium to be a unique catalyst for the polymerization of diolefins to materials of definite and predictable structure, and to have an interesting potential as a direct reducing agent in solvents such as ammonia, amines of low molecular, and ethylene diamine. 

Microcapsules smaller than 10 lm can be formed by the following procedure. The inhibitor is dispersed in an inert gas medium, after which the aerosol is mixed with vapors of a monomer capable of catalytic polymerization of diolefins, triolefins, vinyl esters. Gaseous compounds like NO2, BF3 are used as catalysts. Polymerization runs for about 1-2 min as the suspended inhibitor particles are kept in the reaction zone [27]. 

Ph. Teyssie, M. Julemont, J. M. Thomassin, E. Walckiers, and R. Warin, in The Specific Polymerization of Diolefins by rf-allylie Coordination Complexes (J. C. W. Chien, ed.). Coordination Polymerization A Memorial to K. Ziegler, Academic Press, New York (1975). 

Doi, Y. Tokuhiro, N. Soga, K. Polymerization of diolefins by a soluble vanadium-based catalyst. Kobunshi Ronbunshu 1989, 46, 215-222 Chem. Abstr. 1989, 111, 78655. 

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