Brookhart catalysts

Fig. 2 Single-component, well-defined Brookhart catalyst...

Figure 1.12 Proposed mechanism for conversion of ethylene monomer to dendrigraft polyethylene with Brookhart catalyst at low pressure...

Figure 9. Polymerization of propylene (Rq = CH3) by the Pd-bis-imine Brookhart catalysts.

Very recently, Coates et al. used a vinyl-substituted Upy-unit to be part of an olefin polymerization using the Brookhart catalyst. With small amounts of Upy-units incorporated, the polyolefins showed thermoplastic elastomeric properties.120... 

The Addition Polymerization of Cyclic Olefins 1105 Fig. 4.3 Brookhart catalyst for cyclopentene polymerization. 

Compare the properties of the newer polyolefins made with metallocene (Adv Polym Sci 1997 127 143) and Brookhart catalysts with those of plasticized polyvinyl chloride. 

The results (Table 3) clearly indicate that in the case of the Ni-based Brookhart catalyst the polar monomers are bound by the carbonyl oxygen atom, while in the Pd-systems the n-complexes are preferred. Tables 3 and 4. The difference between the Ni- and Pd-systems has mainly a steric origin with larger repulsive interaction between the occupied d-orbitals on palladium and the oxygen lone-pair orbitals. On the other hand, there is practically no difference in the orbital-interaction contribution (between occupied and virtual orbitals ) to the binding energy between Ni- and Pd-based systems, as far as a... 

Polymerization of Olefins in Supercritical CO2 Using Brookhart Catalyst... 

To explore the possibilities of olefin polymerization in SCCO2, several monomer and catalyst systems have been investigated. Initially, the proof of principle was established by the polymerization of 1-hexene using the Brookhart catalyst in SCCO2. Subsequently, the polymerization of ethylene was studied in detail. Finally, the copolymerization of ethylene with methyl acrylate was assessed. 

Polymerization of Olefins in Supercritical CO2 Using Brookhart Catalyst 1169 Table 8.5 Polymerization of 1-hexene in CO2 and in CH2CI2 for 2 h. 

Polymerization reactions of ethylene were carried out in SCCO2 at different pressures, temperatures, and monomer concentrations using the Brookhart catalyst In addition, the pressure decrease upon polymerization was modeled to determine the reaction rate. Moreover, the polyethylenes have been analyzed in detail by differential scanning calorimetry (DSC) as well as hydrogen and carbon nuclear magnetic resonance ( H and NMR) in order to determine the branching of the polymer produced. 

PolYiverization of Olefns in Supercritical CO2 Using Brookhart Catalyst 1179 Table 8.10 Characterization of the polyethylenes by DSC, H and C NMR. 

In this chapter, the possibihty of using late transition metal catalysts to synthesize polyolefins in supercritical carbon dioxide was demonstrated [43]. The multicomponent phase behavior of polyolefin systems at supercritical conditions was studied experimentally by measuring cloud-point curves as well as by modeling polymer systems at supercritical conditions. The cloud-point measurements show that CO2 acts as a strong antisolvent for the ethylene-PEP system, which implies that the polymerization concerned will involve a precipitation reaction. The model calculations prove that SAFT is able to describe the ethylene-PEP-CO2 system accurately. Solubility measurements of the Brookhart catalyst reveal that the maximum catalyst solubility is rather low (in the order of 1x10 mol L ). However, a number of strategies are given to enhance this value. 

Post-metallocene developments include Brookhart catalysts based on nickel and palladium. These catalysts can incorporate polar monomers such as methyl acrylate into polyethylene chains. They possess chain-walking mechanisms that allow synthesis of various stmctures from HOPE to hyperbranched PE, as shown in Scheme Chain topology depends on the... 

Simple adjustment of temperature and pressure could easily control polymer chain topology. Brookhart catalysts are used in DuPont s Versipol system. Another class of post-metallocenes are Gmbbs catalysts. These catalysts are good for incorporation of polar monomers and particularly suitable for production of specialty low-molecular-weight polymers with reactive functionalities. 

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