Olefin polymerization propene

The chain-end stereocontrol for olefin polymerizations leads generally to lower stereoselectivities (differences in activation energy for insertion of the two enantiofaces generally lower than 2 kcal/mol) than the chiral site stereo-control.18131132 For this reason, the corresponding catalytic systems have not reached industrial relevance for propene homopolymerization. However, some of them are widely used for propene copolymerization with ethene. 

The second major topic in the field of olefin polymerization is that of the tacticity of the polymer [28]. If the olefin being polymerized is less symmetrical than ethylene, stereogenic centers will appear at the polymer, and the arrangement of these stereocenters can produce highly organized isotactic or syndiotactic polymers, as depicted in Fig. 5 for the case of propene polymerization. The alternative is an atactic polymer where the distribution of stereocenters is random. 

This olefin polymerizes with TiCl4/Al(i-Bu)3 (Al/Ti = 1/2) to form low molecular weight polymers [185]. Rates are first order in monomer concentration and from the initial values the apparent propagation rate coefficient is ca. 6 x 10 1 mole sec at 50°C, the activation energy being 9.5 kcal mole . This is very similar to the rates observed with propene and butene-1, and suggests that fep has a comparable magnitude. 

Organolanthanides of several classes were examined by Bochkarev et al. as potential styrene and propene polymerization catalysts.891 Developments of rare earth metal catalysts for olefin polymerization have been highlighted by Yasuda et al. 19S... 

De-aluminated mordenites were claimedto give more active and stable catalysts for toluene disproportionation than conventional H-mordenite. Becker, Karge, and StreubeP studied the alkylation of benzene with ethene and propene over an H-mordenite catalyst. Shape-selective catalysis was found because only ethylbenzene, w-diethylbenzene, p-diethylbenzene, cumene, p-di-isopropylbenzene, and m-di-isopropylbenzene were detected in the products neither o-diethylbenzenes nor higher alkylated products were found. The results are in agreement with earlier transalkylations over H-mordenite. Catalyst aging was caused by olefin polymerization. The selectivity of Be-mordenite... 

Whereas ethylene requires a fairly high temperature for polymerization even in the presence of most of the catalysts mentioned above, the higher olefins as propene, butene, etc., are more reactive and polymerize very readily. Sulfuric acid tends to cause polymerization of the olefins to higher... 

Olefin polymerization kinetics are considered and discussed in many reviews [ 1-6]. In this section, the influence of the main parameters such as the concentrations of catalysts and cocatalysts and time of polymerization on polymerization rate, and the main reactions in the olefin polymerization process will be briefly reviewed. We also consider the problems of deviation from the linear law of polymerization rate with changing monomer concentration, the effect of hydrogen in the ethene and propene polymerizations, as well as the nature of the comonomer effect, which are under discussion in the literature and the natures of which are not yet completely clear. 

One of the most important characteristics of the polymerization process is the dependence of the polymerization rate on monomer concentration. A number of investigations have shown a first order reaction rate with respect to monomer concentration for ethene, propene, and other olefins over a broad concentration range, and the overall rate of olefin polymerization is generally described by the equation ... 

One of the features of olefin copolymerization kinetics is the effect of comonomer on the rate of ethene or propene polymerization during ethene/a-olefin or propene/ a-olefin copolymerization, i.e., the so-called comonomer effect (CEF). The rate enhancement of ethene or propene polymerization in the presence of a comonomer is observed for conventional ZN catalysts [80, 113-123] and for homogeneous [124-133] and supported metallocenes [134—136] and post-metallocenes catalysts [137-140]. The increase in activity was remarked in the presence of such comonomers as propene, 2-methylpropene, 1-butene, 3-methylbutene,4-methylpentene-l, 1-hexene, l-octene,l-decene, cyclopentene, styrene, and dienes. 

Alt, H. G. Zenk, R. C2-symmetric bis(fluorenyl) complexes Four complex models as potential catalysts for the isospecific polymerization of propylene. J. Organomet. Chem. 1996, 512, 51-60. Chen, Y.-X. Rausch, M. D. Chien, J. C. W. C2y- and C2-Symmetric an5a-bis(fluorenyl)zirconocene catalysts Synthesis and a-olefin polymerization catalysis. Macromolecules 1995, 28, 5399-5404. Rieger, B. Stereospecific propene polymerization with rac-[l,2-bis(ti -(9-fluorenyl))-l-phenylethane] zirconium dichloride/methylalumoxane. Polym. Bull. (Berlin) 1994,32,41 6. 

Important for the copolymerization are the different ractivities of the olefins. The principal order of monomer reactivities is well known [187] ethene > propene > 1-butene > linear a-olefins > branched a-olefins. Normally propene reacts 5 to 100 times slower than ethene, and 1-butene 3 to 10 times slower than propene. Table 8 shows the reactivity ratios for the copolymerization of ethene with other olefins. The data imply that the reactivity of the polymerization center is not constant for a given transition metal compound but depends on the structure of the innermost monomer unit of the growing polymer chain and on the cocatalyst. 

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