Phenoxyl end-capping method

For the kinetic study of the polymerization, the structure of the propagating spedes should be identified and the instantaneous concentration should be determined by chemical or physical method. Saegusa et al.176"178 observed the propagating species in the polymerization of monocyclic ethers by ]H NMR spectroscopy and used the Phenoxyl End-Capping method to determine the instantaneous concentration of the propagating species, Eq. (5). Both methods give the same concentrations. 

Saegusa et al. [92--4] carried out studies of the polymerization of THF initiated by the system AlEt3—H20(2 l)—promoter. ECH, PO, and 3-propiolactone (BPL) were employed as promoters. The concentration of active sites was determined by the phenoxyl end-capping method in studies after 1968 or was calculated from yield and molecular weight [92]. The former gave more reliable results. Kinetics could be fitted to eqn. (8). The rate coefficients observed are shown in Table 8. The fep values for the three promoters are almost the same. They are compared with fep values using other initiators in Table 6. The data show that the... 

Kinetic analyses of the polymerizations of these exo and endo isomers have been reported by Guisti et al. [112] and by Saegusa et al. [113, 114]. The former made their kinetic analysis on the basis of the initial velocity observed in the conversion—time curve. As usual, the latter group used their phenoxyl end-capping method. The initiator used was the BF3—ECH system. Polymerizations of both isomers were characterized by slow initiation and fairly rapid termination. In contrast to THF polymerizations, the depolymerization reaction was insignificant and the kinetics were analysed on the basis of the kinetic equation... 

Method (3).In determining [P ] during the THF poljnnerizatlon Initiated by superacid esters the phenoxyl end-capping procedure is shown In Scheme 1. The reaction of sodium phenoxide with the... 

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