Polymerization, activation degree

Piers investigated ferrocenylboranes containing pentafluo-rophenyl substituents as potential cocatalysts in Ziegler-Natta polymerization. The bifimctional borane (83) (M = Fe, X = CeFs) was found to effect methide abstraction from Cp2ZrMe2 under mild conditions. However, significantly reduced polymerization activity was observed with the monoborylated species (81) (M = Fe, X = CeFs). This effect was rationalized by a stronger degree of interaction with the electron-rich iron center, which lowers the Lewis acidity of the boron center. 

A comparison of the polymerization behavior of CpTiC and [MesCsJTiCb (Cp TiCb) under equivalent experimental conditions shows that the Cp derivative gives a higher degree of syndiotacticity in the resulting polymer, much higher molecular weights and predominantly an increased polymerization activity. 

DP E F f f. Ha He AG Degree of polymerization Activation energy, enhancement factor for gas-liquid mass transfer with reaction, electrochemical cell potential Faraday constant, F statistic Efficiency of initiation in polymerization Ca/CaQ or na/nao, fraction of A remaining unconverted Hatta number Henry constant for absorption of gas in liquid Free energy change kj/kgmol Btu/lb-mol... 

Dk DP E Knudsen diffusivity Degree of polymerization Activation energy, enhancement factor for gas-liquid mass transfer with reaction. mVs ft"/s... 

A growing body of literature suggests that while the olefin polymerization active site does consist of a cationic metal alkyl, it is not an isolated cationic site.i2.i6,92,105-109 q-p,g counteranion is likely present as a solvent-separated or contact ion pair see parts a and b, respectively, of Figure 8. The mechanism for ion pair formation and the observed crystal structures of a few of these ion pairs also suggest an added degree of complexity. 

Antiviral activity of chitosan was reported to depend on the average degree of polymerization, the degree of A-deacetylation, the positive charge valne, and the character of the chemical modifications of the molecule (Liu and De Yao 2002). 

Some support materials can be rendered Lewis acidic enough to ionize dialkyl metallocenes. Marks and co-workers have reported (33) that alnmina dried at very high temperatures can react at least to some small degree with both thorium-and zirconium-based metallocene dimethyl species to yield active catalysts for polyethylene. The resulting cationic metal center is believed to remain coordinated to the surface through an Al-O-M Lewis acid/base linkage, at least prior to exposure to ethylene. Hybrid surface/cocatalyst systems based on aluminum alkyl-treated clays have been developed (34) in which the solid substrate appears to play some role in promoting polymerization activity far beyond that expected for non-methyl aluminoxane- or trialkylaluminum-activated catalysts. 

Thus, the present chapter results have been shown the applicability and usefullness of fractal analysis and strange (anomalous) diffusion conception for description of polymerization reactions, catalyzed by nanofillers. The nanofiller introduction in reactionary mixtnre results in two-phase system formation, where a decisive role will be played by interfacial interactions. The polymerization conversion degree is defined by its active (fractal) time. Hence, the ability to control active time gives the possibility of reaction conrse operation. 

Metallocene catalysts usually require a large excess of MAO or MMAO to achieve high polymerization activity. The effect of the amount of dMMAO was investigated by the living polymerization of propene with 4-dMMAO, because the turnover-frequency (TOP) can be precisely evaluated from the number-average polymerization degree (Pn) of produced polymer and fp as PJt. The relation between Pn/fp and Al/Ti ratio is displayed in Fig. 7. The PJt value increased exponentially... 

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