Termination Studies of Non-Propagating Species

Fischer and Paul [31] have studied the termination rate coefficient for small radicals in solution by means of ESR. The different values of kt measured for these species were closely modelled by the Smoluchowski equation. Although the chain-length dependence of termination reactions involves much larger radicals, the study clearly demonstrates that kt will 

An impressive contribution in the area of mimic reactions was made by Horie, Mita and coworkers [85, 103, 117, 183, 188, 193, 194]. They made an extensive study of the diffusion-limited phosphorescense quenching kinetics of fianctionalised polyst50 enes. Not 

The scaling power was again approximately 0.3 [118]. At small chain lengths of the anthracene chain, the Smoluchowski equation was in good agreement with the data. Finally, at higher polymer concentrations. Rouse dynamics scaling were found to become more and 

When considering the features of excimer formation in somewhat greater detail, some comment on this study seems appropriate. The key issue that one should keep in mind when considering these types of mimic studies, is how the lifetime of a pyrene moiety compares to the lifetime of a free radical. In the case of polystyrene, the polymer that the group of Winnik studied, this comparison is not very favorable. One propagation step of this monomer at a moderate temperature of 30 °C (average temperature used in excimer study) takes about 0.2 to 0.3 milliseconds. Not only can one conclude that a time-dependent Smoluchowski equation 

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In the older literature one can encounter quite a number of papers suggesting that bimolecular termination is not chain-length dependent e.g. 36, 66, 68, 139-143] Experimental evidence, however, has disproved these suggestions and numerous papers have proven termination to be chain-length dependent. The evidence takes several forms and has been obtained employing different experimental approaches, which can roughly be divided in three classes (i) termination studies of free-radical polymerizations, (ii) termination studies of non-propagating species and (iii) diffusion-controlled mimic reactions. 

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