Values of the propagation rate constants

A similar technique was used almost simultaneously by Penczek [18, 19] for the polymerisation of bis-chloromethyl oxetan (BCMO) by (i-Bu)3A/-H20 in chlorobenzene. In this system, too, there is termination by reaction of growing centres with polymer, but initiation is slow and the equations are correspondingly more complicated. The authors believe that their value of the propagation rate-constant refers to ion-pairs and is thus k"v, and we see no reason to disagree with their view they also determined k and kt. 

There seems to be no simple correlation between the absolute values of the propagation rate constants given in the literature and the relative reaction rate of the monomers. 

As pointed out in the previous questions many question marks are contained in this equation. Because of many assumptions we are so ignorant about the real value of the propagation rate constant. To the present day not even the magnitude of kp is clear. For the solution of this question kinetic studies with catalyst systems are required for which effyt = 100%. 

From such data it is then possible to derive the absolute values of the propagation rate constants representing the interaction of the growing chain with the incoming monomer unit. These are shown for isoprene and styrene in Table II. Obviously these propagation rate constants are all characterized by a low activation energy as well as an extremely low frequency factor. This is true both for the non-stereospecific polymerization of isoprene in THF as well as for the stereospecific case of isoprene in hexane (although it seems somewhat more extreme in the latter and for the styrene in benzene). 

Number of Active Centers and Values of the Propagation Rate Constants... 

Sawamoto and Higashimura also determined values of the propagation rate constant by measuring at the same time the amount of monomer consumed and the integrated amount of active species. This was done in media of decreasing dielectric con-... 

We have already discussed the work of Sawamoto and Higashimura with p-methoxy-styrene and methanesulphonic acid (Sect. III-E-10). In those same three papers iodine was also tried as catalyst a value of the propagation rate constant was cal-... 

Sawamoto et al. studied the spectroscopic stop-flow behaviour of the polymerisation of styrene and some of its derivatives by triflic acid In ethylene chloride at 30°C. They obtained overall values of the propagation rate constant of about 1 x 10 M s for styrene, p-chlorostyrene and p-methylstyrene. As previously in the same laboratory with p-methoxystyrene, invisible species were held responsible for some or most of the propagation, particularly in media of low dielectric constant, i.e. pseudocationic polymerisation occurs in all these systems and predominates when the polarity of the solvent does not favour ion formation. 

Knowing the forms and orientations of the growing steps, very exact values of the propagation rate constants, /cy. were found for monatomic steps on Ag(lOO) and Ag(lll) faces by this technique. Both constants have the same value within experimental error xv = (1.0 0.05) cm s V... 

The ideal case of the Smith-Ewart treatment actually proposes a rather elegant method for obtaining the absolute value of the propagation rate constant from emulsion polymerization systems, as shown in Eq. (2.26), where N is the number of particles per imit volume ... 

It should be noted that there is a significant discrepancy between the values of 2k determined by the rotating sector method and KESR for some of the radicals in Table VI. At the present time we are inclined to favour the values obtained from hydros carbon autoxidation because values of the propagation rate constant are also obtained by this method, the magnitude of which gives an internal check on the value of 2k. ... 

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