The experimental determination of copolymerization parameters

The rate constants of propagation, fc, or k22, can be derived and determined, although the procedure may not be simple. On the other hand kl2 or k2l are not directly measurable at present. They are usually inferred from experience with copolymerizing systems or with transfers. To date, copolymerization parameters much more frequently serve as the basis for the calculation of elementary constants than the reverse. For their determination, according to eqn. (66), we have to know the populations of Mj and M2 both in the monomer mixture and in the copolymer. In principle, two approaches are known. 

Fineman and Ross [171] proposed another form of graphical evaluation of eqn. (80) 

Equation (80a) is an equation of a straight line with [y - (y/n] as the ordinate and y2/n as the abscissa. For several known pairs n and y, a straight line of slope r, is constructed whose intercept with the ordinate is equal to — r2 (see Fig. 19). 

Tidwell and Mortimer noted that the Fineman and Ross method does not treat experimental data with equal weight, yielding physically unrealistic results in some cases [172]. In order to remove this drawback, Tud6s et al. [173] proposed a modification of eqn. (80) which can also be evaluated graphically 

The main advantage of this equation is that it is possible to check visually assumptions with which the equation has been derived. When these are not fulfilled, the experimental points deviate from a straight line [the slope is a function of both parameters and a compensation of errors is less probable than with the simpler equation (80a)]. 

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