Olefin polymerization correlations

In a quest to increase the efficiency of olefin polymerization catalysts and their selectivity in the orientation of the polymerization, the highly effective Group IV metallocene catalysts, M(Cp)2(L)2, have been studied, since they all display high fluxionality. Following methide abstraction, the metallocene catalysts of general formula M(Cp-derivatives)2(CH3)2 (M= Ti, Zr, Hf), were turned into highly reactive M+-CH3 cationic species. The activation parameters for the methide abstraction, derived from variable temperature NMR experiments, establish a correlation between the enthalpies of methide abstraction, the chemical shift in the resulting cation, and the ethylene polymerization activities [149]. 

The catalytic cracking of four major classes of hydrocarbons is surveyed in terms of gas composition to provide a basic pattern of mode of decomposition. This pattern is correlated with the acid-catalyzed low temperature reverse reactions of olefin polymerization and aromatic alkylation. The Whitmore carbonium ion mechanism is introduced and supported by thermochemical data, and is then applied to provide a common basis for the primary and secondary reactions encountered in catalytic cracking and for acid-catalyzed polymerization and alkylation reactions. Experimental work on the acidity of the cracking catalyst and the nature of carbonium ions is cited. The formation of liquid products in catalytic cracking is reviewed briefly and the properties of the gasoline are correlated with the over-all reaction mechanics. 

In the preceding chapter it has been shown that the DFT methods currently available can be used to reproduce relative trends in both reactivities and transition-metal NMR chemical shifts. Thus, NMR/reactivity correlations can be modeled theoretically, at least when relative reactivities are reflected in relative energies on the potential energy surfaces (activation barriers, BDEs). It should in principle also be possible to predict new such correlations. This is done in the following, with the emphasis on olefin polymerization with vanadium-based catalysts. 

Propylene conversion over three SAPO molecular sieves (SAPO-5, SAPO-11, and SAPO-34) was conducted at a variety of operating conditions. Catalyst behavior was correlated with the physical and chemical properties of the SAPO molecular sieves. The objective of this work was to determine the relative importance of kinetic and thermodynamic factors on the conversion of propylene and the distribution of products. The rate of olefin cracldng compared to the rate of olefin polymerization will be addressed to account for the observed trends in the product yields. The processes responsible for deactivation will also be addressed. 

The purpose of this study was to investigate the mechanism of cationic olefin polymerizations by model experiments using alkyl-aluminum/alkyl halide initiator systems and to correlate the results of model experiments with corresponding polymerization reactions. 

Antberg, M. Dolle, V. Klein, R. Rohrmann, J. Spaleck, W. Winter, A. Propylene Polymerization by Stereorigid Metallocene Catalysts Some New Aspects of the Metallocene Stmcture/polypropylene Microstructure Correlation. In Catalytic Olefin Polymerization, Studies in Surface Science and Catalysis-, Keii, T., Soga, K., Eds. Kodansha-Elsevier Tokyo, 1990 p 501. 

This chapter will discuss all known group 3 and 4 doubly bridged ansa-metallocenes made to date. When polymerization data is unavailable, comments will be made on the perceived viability of the compounds as precatalysts for a-olefin polymerization based on their structure and symmetry. For the a-olefin polymerization precatalysts described herein, the correlation between catalyst structure and polymer tacticity will be discussed. Further, the correlation between catalyst structure and regiocontrol, polymerization activity, and polymer molecular weight will be addressed when there is pertinent data present for a given precatalyst. 

At the same time, the fact that the homogeneous catalyst precursors are structurally well-defined has provided an extraordinary opportunity to investigate the origin of stereospecificity in olefin polymerization at a level of detail that was difficult if not impossible with the conventional heterogeneous catalysts. For example, NMR analysis of the isotactic polymer produced with HI revealed the stereochemical errors mmmr, mmrr, and mrrm in the ratios of 2 2 1 (Fig.5). This observation is consistent with an enantiomorphic site control mechanism, where the geometry of the catalyst framework controls the stereochemistry of olefin insertion.6 30,31 These results established unambiguously a clear experimental correlation between the chirality of the active site, which could be established by x-ray crystallography of the metallocene catalyst precursor, and the isotacticity of the polymer produced. 

Advanced multinuclear solid state NMR experiments were developed to probe the structure of two organometallic aluminum derivatives, which are relevant to olefin polymerization processes. For the first time, NMR observation of Al- C covalent bonds in solids is performed with the natural abundance material. Triple-resonance ( H- C- Al) and quadruple-resonance ( H- Li- C- Al) heteronuclear correlation two-dimensional NMR experiments are also introduced to probe Al- C and proximities. ... 

Kennedy, J. P. and Rengachary, S. Correlation Between Cationic Model and Polymerization Reactions of Olefins. Vol. 14, pp. 1 —48. 

S. Rengachary Correlation between Cationic Model and Polymerization Reactions of Olefins. 

Correlations presented in the middle thirties enabled the prediction of octane number improvement resulting from thermal reforming (7, 21). They have continued to appear in the literature (6, 20). Improvement of the octane number of naphthas has been the principal function of thermal reforming, but Egloff (8) discusses its usefulness also for the production of light olefins which provide feed stocks for alkylation or polymerization processes. To show the distinct improvement in the yield-octane relationship realized by the catalytic polymerization of C3 and C4 olefins produced by thermal reforming, Mase and Turner (16) present experimental data at various reforming severities for two naphthas. 

The polymerization of light olefins using copper pyrophosphate is licensed by The M. W. Kellogg Co. under patents of the Polymerization Process Corp. The process is essentially the same as the U.O.P. process but instead uses a copper pyrophosphate catalyst (18). The first plant was built in 1939 (22) and several more have been put into operation since that time. A correlation of operating variables for this process was published in 1949 (21) it shows how conversion is influenced by catalyst activity, temperature, ratio of propene plus n-butene to isobutene, and the space velocity of olefins and of total feed when operating at 900 pounds per square inch gage pressure. A catalyst life of 100 to 150 gallons of polymer per pound of catalyst is claimed (15). 

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