Soluble polymer-supported materials

In a differing approach to the development of insoluble, supported catalytic materials, the use of soluble polymer supports offers a possible method to facilitate the separation, subsequent recovery, and reuse of catalyst complexes. It is important to note that this often requires relatively large quantities of a non-solvent for the precipitation and recovery of the catalytic material. This is an obvious limitation, as the excess waste generates an environmental concern however, other techniques can be employed to facilitate the recovery. Examples of this include liquid/liquid phase separations or the selective precipitation of the product or catalyst from the reaction media through the use of different stimuli, such as temperature or pH. 

Ten millilitres of the standard catalyst used previously in this section is mixed with different soluble reducing agents. An even, homogeneous layer of catalyst which is obtained by mixing 10 ml of catalyst, such as I ml of nBuLi, is applied to a flat carrier consisting of a polymer-supporting material (HOPE or polypropylene films). Acetylene is then introduced and allowed to react with this modified catalyst to give a new (CH) film. 

Among the earliest studies was that of Moffat (105). Poly-2-vinylpyri-dine, cross-linked with 4-8% divinylbenzene, was used as the coordinating support. The amount of cross-linking was found to be critical too little gave a soluble polymer, while too much gave an intractable material which absorbed little metal. Cobalt was used as the catalyst, and the reaction was conducted at 150°-200°C and 2000-3000 psi of 1/1 H2/CO. 

In a cryptate complex, the cation is enclosed wholly or partially in a hydrophobic sheath, so that not only are salts of this complexed cation soluble in nonpolar organic solvents but also extractable from aqueous solutions into organic solvents immiscible with water (144). Specific cryptands may be used to selectively complex metals from crude materials or wastes, particularly if they are immobilized on a polymer support (101, 114, 145). 

Reichert and Mathias prepared related branched aramids, to those of Kim,t5-34] from 3,5-dibromoaniline (23) under Pd-catalyzed carbonylation conditions (Scheme 6.7). These brominated hyperbranched materials (24) were insoluble in solvents such as DMF, DMAc, and NMP, in contrast to the polyamine and polycarboxylic acid terminated polymers that Kim synthesized, which were soluble. This supports the observation that surface functionality plays a major role in determining the physical properties of hyperbranched and dendritic macromolecules J4,36 A high degree of cross-linking could also significantly effect solubility. When a four-directional core was incorporated into the polymerization via tetrakis(4-iodophenyl)adamantanc,1371 the resultant hyperbranched polybromide (e.g., 25) possessed enhanced solubility in the above solvents, possibly as a result of the disruption of crystallinity and increased porosity. 

Metallocenes immobilized on solid support materials have been successfully introduced in industry as polymerization catalysts for the production of new application-oriented polymer materials. Industrial polymerizations, which are carried out either as a slurry process in liquid propylene or as a gas-phase process (Section 7.2.3), require that catalysts are in the form of solid grains or pellets soluble metallocene catalysts thus have to be supported on a solid carrier. 

---