Ab initio polymerizations

The population balance equations are very general and may be applied to batch, semicontinuous, and continuous emulsion polymerizations. Furthermore, both seeded and ab initio polymerizations are comprehended by Eq. (5) in all (or part) of the three commonly considered polymerization intervals. The following sections show how the different possibilities are reflected in different functional forms of the elements of the matrices O and K and of the vector c. It should be remembered, however, that certain conceivable situations are not comprehended by Eq. (5) for example, if the monomer molecules are not freely exchanged between the latex particles so that the monomer concentration inside each latex particle is determined by its growth history. 

Secondary nucleation can also be used to produce bimodal or multimodal PSDs. This can be done in several ways by means of seeded [170] or ab initio polymerizations [171-178]. Miniemulsion polymerization can also be used to produce broad PSDs [179, 180],... 

Besides seed and feed procedures, batch polymerizations with a free monomer phase are also very popular. In these so-called ab initio polymerizations, water, emulsifier and monomer are charged into the reactor and allowed thermally to equilibrate under gentle stirring. Then, the polymerization is started by adding initiator. The stirrer speed is, compared to suspension polymerization, only of minor importance as both the final particle sizes and particle properties are not governed by the... 

ProCGdures. From a technological point of view heterophase polymerizations can be carried out either batchwise, semicontinuous (or semibatch), or continuous. In the batchwise case the reactor is filled with all ingredients before the polymerization is started and the reactor content is removed at the end of the polymerization. In a semibatch procedure, at the start of the poljunerization the reactor is filled only partially and a stream of either neat monomers or monomer emulsion with constant or deliberately changed composition is fed continuously until the reactor is filled. After a final post-feeding batch reaction period, the reactor is emptied. A continuous procedure means that all necessary ingredients are fed and final latex is removed continuously. In all three cases the poljunerization can be carried out in the absence or presence of preformed particles (so-called seed particles). Reactions in the absence of seed particles are frequently called ab initio polymerizations and require that particle nucleation takes place. Table 7 is an... 

Meier, R.J., Van Doremaele, H.J., larlori, S., Buda, F. Ab-initio molecular dynamics study of metallocene-catalysed ethylene polymerization. J. Amer. Chem. Soc. 116 (1994) 7274-7281. 

The y and mean y values computed at different theoretical levels are given in Table 1. We can see that the hyperpolarizability increases with the extension of the polymeric chain. It is worth noting that our MNDO values agree with the ab initio ones of Kurtz[15] but do not vary in a parallel direction to the CNDO results of Waite and Papadopoulos[7]. Note that the CNDO values are the closest to the experimental data for butadiene and hexatriene, but these latest data have been used to fit the CNDO parameters. Furthermore, the results... 

However, this kind of compounds has not been extensively studied theoretically [12,15], At the semi-empirical level, we point out the MNDO calculations of Williams [12] concerning chains of less than 14 carbon atoms, and the fNDO computations of Kirtman [15[ related to polymeric chains containing up to carbons. To our knowledge no ab-initio evaluation of... 

We note that, as previously, y and increase with the lengthening of the polymeric chain. It is worth noting that the MNDO results vary in a parallel manner with the ab initio... 

Recently, theoretical calculations were done on the olefin polymerization. In particular, an ab-initio molecular orbital calculation was used to optimize the geometry for the ground, transition and product states of model systems, based on gas-phase reactions ... 

Studies on borohydride complexes of post-transition metals are as follows. Theoretical calculations on M(BH4) (M = Cu, Ag, Au) at the ab initio level indicate that Cu(i) and Ag(i) congeners have tetrahydridoborate structures, while the gold complex adopts a hydridoborane structure HAu(BH3).37 MeZn 2 /-BH4) 30 is prepared by addition of B2H6 to ZnMe2 or MeZnCl and Li[BH4]. The X-ray structure shows a polymeric helical arrangement of ZnMe + and [BH4]- fragments—similar to Be(BH4) or H2Ga(BH4) 50.38... 

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