Propene polymerisation

Inhibition of a catalytic reaction by impurities present may take place and sometimes this may have a temporary character. If it is permanent one cannot be mistaken in the kinetic measurements. Impurities that are more reactive than the substrates to be studied may block the catalyst if they react according to a scheme like that of Figure 3.7. Only after all inhibitor has been converted the conversion of the desired substrate can start. Another type of deactivation that may occur is the formation of dormant states, which is very similar to inhibition. Either the regular substrate or an impurity may lead to the formation of a stable intermediate metal complex that does not react further. There are examples where such intermediates can be rescued from this dormant state for instance by the addition of another reagent such as dihydrogen (Chapter 10, dormant states in propene polymerisation). 

Another, independent development involves vanadium catalysed propene polymerisation leading to syndiotactic polypropylene [20], see 10.2.1. 

F and B NMR spectroscopy. The rate of propene polymerisation with this system was only three times faster than that of 1-hexene. This slow rate contributes to the high regioselectivity of the polymerisation no 2,1-propene misinsertions were detected. H and NMR spectroscopy also provided information about the chain termination mechanism here this occurred by p-H elimination in a first-order process. Polymer chain-end epimerisation, i.e. chirality inversion at the P-carbon of the polymer chain (Scheme 8.31), proceeded via a zirconium tert-alkyl (rather than tt-allyl) intermediate [96c]. 

Tudor J, Willington L, O Hare D, Royan B (1996) Intercalation of catalytically active metal complexes in phyllosilicates and their application as propene polymerisation catalysts. Chem Commun 17 2031-2032... 

Four new asymmetric ansa-zirconocene dichlorides, rac-[l-(9-ri -fluorenyl)-2-(2-phenyl-l-ri -indenyl)ethane]zirconium dichloride, rac-[(9-ri -fluorenyl)(5,6-cyclopenta-2-methyl-l-ri -indenyl)dimethylsilane]zirconium dichloride, rac-[(9-ri -fluorenyl)(2-methyl-l-ri -indenyl)dimethylsilane]zirconium dichloride and rac-[(9-r -fluorenyl)(2-phenyl-l-ri -indenyl)dimethylsilane]zirconium dichloride, have been prepared and evaluated as propene polymerisation catalysts. The synthesis of the [2,5-diisopropylcyclohexane-l,4-bis(indenyl)]titanium dichloride and [2,5-diisopropylcyclohexane-l,4-bis(tetrahydroindenyl)]titanium dichloride complexes, shown as 20, and their use as catalysts for the enantioselective pinacol coupling of benzaldehyde have been described. ... 

Fig. 9.53 Kinetic model for polymerization including deactivation. (From E Ochoteco, M. Vecino, M. Montes, J.C de la Cal, Kinetics and properties in metallocene catalysed propene polymerisations, Chem. Eng. Sci. 56 (2001) 4169-4179. Copyright 2001 Elsevier).

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