Internal donors

Yu, G., Gao, J., Hummelen, J.C., Wudl, F., and Heeger, A.J. (1995) Polymer photovoltaic cells enhanced efficiencies via a network of internal donor-acceptor heterojunctions. Science 270, 1789-1791. 

Heterocyclic Systems with Internal Donor Atoms... 

G. Yu, AJ. Heeger, Charge separation and photovoltaic conversion in polymer composites with internal donor/acceptor heterojunctions, J. Appl. Phys. 78 (1995) 4510 1515. 

External donors are introduced together with the organometallic cocatalyst. In the absence of external donor, the organoaluminium component (e. g. Et3Al) rapidly reacts with the internal donor. The external donor reduces the rate of internal donor consumption and/or substitutes its loss [286], Chemically, external donors are very similar to internal donors, and they may even be identical. 

The International Donor Community, Governments and International Financial Institutions should ... 

A comparison between the productivity trends of binary and ternary catalysts in the presence of an external donor proves to be quite interesting. While the atactic fraction productivity has a similar behavior for both catalysts, the binary catalyst shows a decrease of isotactic productivity with increased D/Al ratio the ternary catalyst, on the other hand, shows a maximum (see Fig. 40). This is still in agreement with the Burfield model. In fact, these results can be accounted for by assuming that the internal donor gives rise to the formation of a new type of isospecific center, characterized by kA and kD values different from those present in binary catalysts. The presence of a maximum in productivity is consistent with the formation of complexes between the aluminum alkyl and the donor and the resulting modification of the adsorption equilibrium, as suggested by Burfield1S6>. 

Although intermolecular interaction is stronger, the use of an internal donor is reasonable as it is easier to keep in place and simultaneously provides steric protection. 3 should be sufficiently stable to prevent fast dimerization and should enable the isolation of a diaminosilylene with perpendicular arrangement of the amino substituents. 

Most recently, a further family of MgCl2-supported catalysts has been developed,344 345 in which the internal donor is a succinate rather than a phthalate ester. As is the case with the phthalate-based catalysts, an alkoxysilane is used as external donor. The essential difference between these catalysts is that the succinate-based systems produce PP having much broader molecular mass distribution, discussed in Section 4.09.3.4. 

A Guide to Competitive Vouchers in Health is directed to international donors and health care providers and policymakers in developed and developing countries. 

Analytical studies have indicated that a monoester internal donor such as ethyl benzoate is coordinated to MgCl2 and not to TiCLj. In the search for donors giving catalysts having improved performance, it was considered that bidentate donors should be able to form strong chelating complexes with... 

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