Stabilizer polymer homogeneous dispersion

The entropy of NCs and conjugated polymers mixing is low. Thus, in order to stabilize a homogeneous dispersion of quantum dots in the polymer matrix it is necessary to increase the interactions between the NCs capping ligands and the polymer chains. In this respect, the application of supramolecular chemistry concepts such as, for... 

Highly effective catalysts have been prepared by using the protective properties of some hydrophilic polymers, such as polyvinylpyrrolidone (PVPD), polyvinylmethyl ester (PVME), dextrin and PVA. The protective role of these synthetic polymers is to prevent the aggregation of colloidal metal particles and to stabilize the homogeneous dispersion of small particles. These catalysts possess high activity and selectivity. They are, moreover, easily separated from reaction products and can be repeatedly reused [36, 37]. 

Micron-size particles can also be prepared by polymerization of monomer dispersion in organic solvents (e.g. alcohol) in which the emerging polymer is not soluble. At the beginning of the process, the reaction mixture is homogenous but during the reaction, stabilized polymer particles precipitate. This method offers uniform particles with a diameter of 2-15 pm (40). 

Colloidal metal clusters, which offer a high surface area for better activity, have been stabilized by polymers. Thus, a homogeneous dispersion of a cobalt-modified platinum cluster was stabilized by a coordinating polymer, poly(/V-vinyl-2-pyrrolidone).74 Addition of the cobalt(II) [or iron(III)] doubled the activity and increased the selectivity from 12 to 99% when the catalyst was used to reduce cin-namaldehyde (5.23). 

The introduction of the UV-stabilizer in PUs was made by different ways. The first kind of stabilized polymer (a) was obtained by adding a solution of BHMBE in DMF (cone. = 4.34 g/100 ml) under stirring into the melted prepolymer. The solvent DMF was then removed by vacuum distillation, and the chain extender was added. A polyurethane containing 0.58% BHMBE was obtained (Fig. 4.60). A PU sample obtained by introducing the powdered UV-stabilizer in the macrodiol directly (forming a dispersed phase) presented poor mechanical properties because of their less homogeneous structure [64]. 

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