Solid support catalysts polyethylene

All peptide-catalyzed enone epoxidations described so far were performed using insoluble, statistically polymerized materials (neat or on solid supports). One can, on the other hand, envisage (i) generation of solubilized poly-amino acids by attachment to polyethylene glycols (PEG) and (ii) selective construction of amino acid oligomers by standard peptide synthesis-linked to a solid support, to a soluble PEG, or neat as a well-defined oligopeptide. Both approaches have been used. The former affords synthetically useful and soluble catalysts with the interesting feature that the materials can be kept in membrane reactors for continuously oper-... 

Systems have been developed that allow the recycling of catalysts. The first case study involved simple adsorption of proline onto silica gel [6], but the system suffered from a loss in enantioselectivity. More recently, promising results have been obtained with fluorous proline derivatives [64] used for aldol reactions the recycling of fluorous catalysts has been demonstrated using fluorous solid-liquid extraction. Solid phase-supported catalysts through covalent bonds [65] and through noncovalent interactions [66] were also used for aldol reactions. Proline and other catalysts can be recycled when ionic liquids or polyethylene glycol (PEG) were used as reaction solvents [67]. 

Various polymeric and solid supports, such as polyethylene glycol (PEG), can be used to immobilise these catalysts.[46 48] Exchanging the polymer support on the styrene moiety for charged ionic liquid tags affords complexes 38 and 39, which are retained to a significantly higher degree in the ionic liquid phase (Scheme 7.4). 

The primary products from iron catalysts are linear polyethylenes and aluminum polymeryls. The iron complexes can be prepared in a few simple steps and are not particularly sensitive to air, contrasting with many metallocenes of group 111 and IV or rare earth complexes. A body of literature on ethylene polymerization studies with these complexes allows a picture to be created of the catalytic action [31]. Here, a summary is given oti the catalytic activity of these complexes, also in combination with solid supports, and an outlook towards the preparation of composites. 

The heterogeneous catalyst was prepared by reacting 0.5 g of silica containing MAO within the silica pores with 25 mg of complex 24 and 10 ml of additional toluene and 5 ml of additional MAO/toluene solution. The contents of this slurry were stirred and ethylene was added (1 atm) to initiate a prepolymerization process that was carried out to increase the total solids to 2.06 grams which were isolated by solvent evaporation in vacuo. The silica-supported catalyst was evaluated in a 2-liter reactor containing one liter of isobutane at 80°C, 35 bar total pressure with TIBA as cocatalyst. Linear polyethylene was produced with an M of 1470 and M M of 2.13 with a catalyst activity of 1309 Kg PE/g Cr/hr. These results clearly demonstrate that this particular single-site catalyst could be operated in commercial polyethylene manufacturing operations. 

As discussed above with Chevron-Phillips metallocene-based catalyst which is activated with solid acid catalyst supports, the introduction of low levels of long-chain branching is an important structural feature of polyethylene manufactured for commercial applications with single-site catalysts. Dow s CGC system is able to incorporate low levels of long-chain branching into the polyethylene due to the high level of vinyl-terminated polymer molecules, the relatively high polymerization temperature that is... 

Based on the requirements outlined above, industrial scientists recognized soon after the discovery of single-site catalysts based on zircono-cene/MAO solutions that this type of catalyst needed to be supported on a solid support in order to manufacture polyethylene in commercial reactors based on the slurry process and the gas-phase process. Therefore, suitable supports for the single-site Zr/MAO catalyst systems must meet similar requirements as other catalysts in order to perform satisfactorily as particle-form catalysts. 

A number of other chemical modifications of polymers have been performed under phase transfer conditions Including the cleavage of peptides from a solid support in a Merrlfield solid phase synthesis (Ref. 65), and the hydrolysis of methyl methacrylate in the presence of catalysts such as polyethylene glycol or 18-crown-6 (Ref. 66). Hradil and Svec (Ref. 67) have very recently completed a study of the reaction of hydrolyzed copoly(glycldyl methacrylate ethylene dimethacrylate) with propane sultone in the presence of tetrabutyl ammonium hydroxide. While the reaction gave only 25% yield in the absence of catalyst, a drastic improvement to 68% conversion was observed when a phase transfer catalyst was added. 

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