Mayo plot

Figure 6.1 Mayo plots" in which the calculated limiting slopes (triangles,------,...

Fig. 24. Mayo Plots of oeMeSt polymerization using the HSifCH CHjCH CHjQ/Me Al initiating system (See Table 7 for reaction conditions)...

The activation energy differences of My as well as of and M, and k /kp and kt/kp. were calculated from Arrhenius and Mayo plots, respectively, by linear regression analysis using a computer. Hie AEjjw values given in kcal/mole can be converted to kJ/mole by multiplying with 4.18. 

Analysis of Molecular Weight Controlling Events Using Mayo Plots. 138... 

This section concerns studies directed toward an elucidation of relative rate constants, k,./kp and kt/kp, and a mechanistic interpretation of these parameters. The data for the HMWF of PIB samples prepared with 7-BuCl and f-BuBr/Et2AlCl/MeCl systems shown in Table 7 were calculated from Mayo plots (see also p. 56 for Mayo Equation) using M data given in Tables 4 and 5. The data of LMWF of PIB prepared with f-BuBr/Et2AlCl/MeCl system at —50 °C shown in Table 7 were calculated from Mayo plots using M data given in Table 5. 

Fig. 7. Mayo plots based on GPC Mn values of PIB prepared with r-BuX/Et2 AICI/MeCl at -50 °C and -60 °C...

Table 7. Comparative study of kinetic parameters obtained using Mayo plots of Mv and Mn of PIB...

Mayo plot provides relative rate constants of the molecular weight controlling events22. Transfer and/or termination with solvent, polymer and impurities are assumed to be negligible. Although the Mayo equation is strictly valid only for data obtained at low conversion, Plesch23 has shown that the plot provides remarkably reliable information even with data obtained at relatively high conversions. 

The present study concerns the effect of isobutylene concentration on P1B Mv using r-BuCl/Et2AlCl/MeCl and r-BuBr/Et2AlCl/MeCl systems at various temperatures. Figures 14 and 15 and Table 6 contain the data obtained using the r-BuCl initiator system. Significantly, the Mayo plots showed an absence of intercepts, i.e ktr/kp ar 0, and kt/kp = 3.75 x 10"4,3.21 x 10 4 and 2.49 x 10 4 at -40°, -50°... 

Figure 16 shows the Mayo plots obtained with the f-BuBr/Et2AlCl/MeCl system at —30° and —50 °C. These plots exhibit significant intercepts, i.e., ktr/kp =... 

Fig. 14. Mayo plots based on Mv s of PIB s prepared with r-BuCl/Et2AlCl/MeCl...

Comparisons of relative rate constants obtained with Mv s of the total polymer and M s of the HMWF for the same samples show similar trends negligible transfer and termination control of molecular weights for the f-BuCl/Et2AlCl/MeCl system in the —40° to —60 °C range and also for the f-BuBr/Et2AlCl/MeCl at —50 °C (Table 7). For the samples prepared with the f-BuCl/Et AlCl system Mayo plots based on Mv s show zero intercept while that based on Mn s of the HMWF shows a small but finite intercept, z., ktr/kp = 1.91 x 10-5 and 2.14 x 10-s at —50° and -60 °C. Similarly, for the samples prepared with the t-BuBr/Et2AlCl system the Mayo plot based on Mn s of HMWF shows zero intercept while the Mayo plot based on Mv s show a very small intercept, ie., ktr/kp = 5.0 x 10-s at —50 °C. The reasons for this small discrepancy are not known. 

A hypothesis suggesting a relation between the AEmv and molecular weight governing mechanisms has been proposed, which state that AEmv s = —6.6 + 1.0, -4.6 +1.0 and —1.8 1.0 reflect three different molecular weight governing mechanisms transfer to monomer, a combination of transfer to monomer and termination, and termination, respectively. Experimental proofs in support of this hypothesis have been obtained by Mayo plot analyses and model experiments. 

Another innovation is the reinterpretation of the significance of the various chain-breaking constant ratios which several workers had determined by means of Mayo plots. 

The degree of polymerisation. The variation of the DP with the concentrations of isobutene, stannic chloride, and water is best represented in the form of the Mayo plots shown in Figures 10, 11 and 12 which were constructed from Norrish and Russell s... 

Figure 11 The variation of DP with [H20] at -78° in ethyl chloride. [i-C4H8] = 3.22, [SnCl4] = 0.185 mole/l [31]. Mayo plot...

The third Mayo plot, (Figure 12), 1/DP against [SnClJ, has a discontinuity at a stannic chloride concentration corresponding approximately to [SnCl4]/[H20] = 1. The rising branch of the curve can be represented by a line of intercept L = 2 x 10"5 and slope S, = 8 x 10-3 1/mole. 

It is an obvious next step to identify this termination reaction with the second order chain breaking reaction involving the agent X, which was shown up by the Mayo plots. The rate of this is given by the third term of equation ii ... 

The overall rate constant was reported [75a] to have the value 0.35 1 mole 1 min"1 at -78.5°. According to our interpretation this is From the Mayo plots and... 

The slope of the Mayo plots was interpreted again as kjk and the reasons why this is probably invalid have been explained above. 

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