Chemical Structure of the Growing Species

Recently, a series of works have been published on the cationic po merization of lactones (e.g. p-propiolactone and e-caprolactone ) and various ionic ecies have been reported together with elaborate kinetic treatments and some electrochemical measurements. In our opnion the chemical structure of the growing species in the cationic polymerization of lactones has not yet firmly been established (see also Ref. 190) and, therefore, a more detailed discussion of the% interesting and important systems must wait until these structures are known. 

Correlations of structures and reactivities require for the ring-opening polymerization as well as for other ionic polymerizations approaches differing from these in radical polymerization of the unsaturated monomers. This is because in radical polymerization free radicals are the unique chemical structure of the growing species and double bonds are the only chemical groups involved in polymerization (1), C ). ... 

Anionic polymerization. For some heterocyclic monomers the unique chemical structure of the growing species follows unequivocally from the monomer structure. However, in many cases isomeric structures have to be taken into account. For instance, for symmetrical monomers, like thietane, the carbanion but not the thiolate anion was proposed (4). Unsymmetrically substituted monomers can provide active species by a- or B- ring scission. Unusual structure of activated monomer was proposed for NCA and lactams. These structures can not be distinguished by spectrophotometric methods, and application of H- or 13C-NMR looks more promising. 

Although end-capping methods allow the concentration of the growing species to be measured, but no information about their chemical structures can be obtained in this way. 

In order to terminate a growing polymer chain, it is necessary to effect the removal of the free radical from the polymer chain. This may be accomplished in one of several ways, but all involve either a combination reaction, a disproportion reaction or a transfer reaction. The exact mechanism will be dependent on the chemical structure of the monomer, the polymer chain and the nature of any other species present. 

The structure of the EDL is neither simple nor universal it depends to a great extent on the physico-chemical properties of particles and dispersion medium. In general, it is assumed that some ions from the solvent adhere on the particle surface and partially neutralise the surface charge. This layer of immobile ions is called Stem layer. The other ions spread in the solvent by thermal motion yet are subject to the electric field generated from the charged surface. With growing surface distance the concentrations of the ionic species tend to their equilibrium values of the free solvent. The region adjacent to the Stem layer with excess of counter-ions is called the diffuse layer. In this part of the EDL, the ion distribution results from the balance of electrostatic and osmotic forces. 

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