Pseudoion

Seeded dispersion polymerization was extensively investigated for radical systems [17]. Much less is known about seeded dispersion polymerizations with propagation on ionic and/or pseudoionic active centers. Awan et al. reported seeded ionic polymerization of styrene, which at certain conditions produced particles with narrow diameter size dispersity [18,19]. We presented the first data on the seeded ring-opening polymerization with constant number of microspheres. 

Closely related to the ionic polymerization of heterocyclic monomers is, what we can call, pseudoionic polymerization (or sometimes, perhaps, cryptoionic). We use the preffix pseudo- in the same meaning as it was first used in the vinyl cationic polymerization. It means that propagation actually proceeds on the covalent species that could have been in equilibrium with their ionic counterparts. Several systems falling to this category have recently been described for both anionic and cationic polymerization of heterocyclics. In the anionic processes derivatives of Zn or A1 alkyls or alcoholates are believed to function this way. However, for none of these systems the absence of ionic contribution was shown. Two catalytic systems are of particular interest, namely the -Zn-O-AK systems (20) and>Al-alkyl modified by bulky porphyrin derivatives (21). Both are discussed in this volume and both have been clearly shown to produce living systems. The former with e-caprolactone and the latter... 

The foundation of the "rigid-pseudoion" model is the "rigid-ion" description of the lattice dynamics, which was introduced by Nordheim. In this approximation, the ion-core potential of an atom moves rigidly when the atom is displaced from equilibrium. Thus, the potential seen by an electron due to a lattic of such atoms is justr, 24,27,28... 

However, the agreement which we have obtained through our potential is good and can be taken as a demonstration of the validity of the "rigid-pseudoion" model for calculating EP and HP matrix elements. 

Based on the success of both our calculations and those of Ref. 12 we conclude that the "rigid-pseudoion" model provides a good description of the EP and HP intervalley scattering matrix elements in Ge and Si. One of the questions to be resolved is the difference in the extrapolation of the form factor between our work and that of Ref. 13. This may be due to the empirical nature of the pseudopotential that has been used and suggests that a more self-consistent approach should be tried. Also the extension of the present work to zincblend-type materials is an area of considerable interest. 

A large majority of cyclic monomers polymerize by one of the ionic or coordination (so-called pseudoionic) mechanisms. Moreover, kinetic poiymerizabiiity and the difference in the rates of polymerization depend on the used conditions and may vary dramatically. In CROP there is no difference between the reactivities of ions and ion pairs, but in anionic... 

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