Cationic polymerization absolute rate constants

Since the determination of absolute rate constants is one of the most urgent problems in cationic polymerization, and the styrene-perchloric acid system seemed to be so clean and simple, Gandini and Plesch set out first to check Pepper and Reilly s results by determining spectroscopically the concentration of carbonium ions during polymerization, and they intended then to extend the method to other monomers. However, their findings were not as expected. A comparison of spectroscopic and conductivity measurements with rate measurements in an adiabatic calorimeter showed [4] that in methylene dichloride solution ... 

These considerations show that the determination of the number and nature of growing species in cationic polymerizations is, in general, not easy, and the alleged determinations of absolute rate constants need to be scrutinised most carefully from this point of view. 

It is the author s hope that the foregoing detailed discussion has helped to clarify some features of cationic polymerizations. Many other aspects, such as co-polymerization and radiation polymerization, which I have not been able to discuss here, deserve equal attention. But perhaps the most urgent task, and one which is much more widely relevant, is the elucidation of details of reaction mechanism, and in particular the identification of the chain-carriers in many widely differing systems. The next problem then is to measure their concentration, its variation throughout the reaction, and, hence, the absolute rate constants. It is essential that the factors which decide whether a polymerization is ionic or pseudo-ionic be determined as soon as possible. 

During the 1970s, when the field of Hving cationic ROP underwent extensive developmenf the absolute rate constants were determined only for THE [106]. Nonetheless, a number of kinetic investigations were conducted with the cationic polymerization of substituted aziridines [121] and 1,3-oxazoHnes [122-124], and this in turn led to the revelation of a variety of attributes of livingness associated with these processes. 

The absolute rate constants of propagation have also been determined in cationic ROP [145-148], although full kinetic analyses have only been performed for THF [146], oxepane [147] and conidine [148] polymerization. 

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