Phosphynated polymers

Since the late 1990s, new approaches to the dispersion of noble metal particles in polymer matrixes by means of chemical, photochemical and radiation-chemical reduction, the evaporation of metal atoms (including solvated ones) into different supports, etc. have been developed (see Section 8-1) [44]. Nevertheless, catalysts prepared from individual immobilized metal clusters have more definite, mostly predetermined, structures. For these purposes derivatives of Oss, It4, RU4, Rh4, Rh6, etc. clusters are most often used. Earlier studies [46] showed that the rate of ethylene hydrogenation promoted by tetrairidium or tetraruthenium carbonyl clusters bound to phosphynated polymers decreased with an increase of the number of donor... 

The dispersivity of Rh° particles formed on the surface of phosphynated CSDVB (2% DVB) and their fractions in relation to the total metal content also depends on the P/Rh ratio. The general tendency is as follows. The rate of butadiene-1,3 hydrogenation reaches a maximum at P/Rhj 1, and does not depend on this ratio at P/Rhs >2. A decrease in the phosphorus content in the polymer as well as the P/Rhs ratio leads to an increase of Rhj particle size at low phosphine-group content and P/Rhj values approaching the Rhs particle size formed on the unfunctionalized polymer (nonmodified CSDVB) (Table 12-3). 

A particularly interesting phenomenon is the conformation of the polymer matrix that provides the favored configuration for the catalytic center. To illustrate this point let us describe the abnormal Arrhenius dependence of the ethylene hydrogenation rate in the gas phase by rhodium complexes immobilized on phosphynated polystyrene [41], A sharp increase of hydrogenation rate has been observed when the temperature increases across the glass transition point, Tg, of the polymer (341 K Fig. 12-4). 

Let us briefly summarize the state of the art in the polymerization of other monomer groups in the presence of polymer-boxmd metal complexes. Considerable progress has been achieved in polymerization of dienes, namely, butadiene and isoprene, catalyzed by macromolecnlar complexes based on rare earth halides [114], Co-oligomerization of 1,3-butadiene and CO2 with immobilized palladium complexes (phosphynated PS as macromolecnlar ligand) [115] and polymerization of acetylene monomers with immobilized complexes of Mo(V), W(VI), and Pd(II) have been developed though they have not been investigated intensively. 

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