Anionic ring-opening polymerization characteristics

These anionic ring opening polymerizations are usually carried out either in bulk or in solution. A host of catalyst types are active. For synthetic references using specific catalysts, the reader is referred to several excellent sources (4,7,31,32). Representative catalysts include hydroxides, alcoholates, phenolates, silanolates, siloxanolates, mercaptides of the alkali metals, organolithium and potassium compounds, and quaternary ammonium and phosphonium bases and their silanolates and siloxanolates. Some physical characteristics of linear oligomers are given in Table 5 (10). 

The above type of reaction is characteristic of the so-called polymer reactions . The rate itself and the activation parameters may be quite different from those of the conventional anionic ring-opening reaction of epoxides. In the above reaction of a polymeric epoxide, a polymer consisting of 77% THF. diyl units and 16% epoxide units was isolated in a soluble form. If the opening of the epoxide ring by an alkoxide group had occurred in a random fashion, cross-linking would have taken place to produce an insoluble polymer. 

Ionic ring-opening polyerizations show most of the characteristics described in Chapter 8 for cationic and anionic polymerizations of vinyl monomers. Thus they show effects of solvent and counterion, propagation by different species (covalent, ion pairs, and free ions), and association phenomena analogous to those discussed in Chapter 8. 

---