Termination by Coupling, Disproportionation, and Chain Transfer

For polymerization where termination occms by all three modes, namely, coupling, disproportionation, and chain transfer, one can derive the size distribution as a weighted eombination of the above two sets of distribution functions. For example, the weight distribution can be obtained as (Smith etal., 1966)  

To calculate P and to, and hence Wx, from kinetic and theoretical considerations for any polymer system, it is thus necessary to have the values of transfer constants (Cm, Cj, Cs), k lkt, kt, and 

In as much as polymerization rates are measured at less than 10% conversion, it can be assumed that [M] and [I] in Eq. (6.188) are equal to their initial concentrations. Therefore, 

Since kdlikc + hd) = 0.85 and ktc + kd = h = 2.55X10 Lmol it follows that ktd = 2.167X lO Lmol Therefore, 

Problem 6.35 The bulk polymerization of methyl methacrylate (density 0.94 g/cm ) was carried out at 60°C with 0.0398 M benzoyl peroxide initiator (Smith et al., 1966). The reaction showed first order kinetics over the first 10 15% reaction and the initial rate of polymerization was determined to be 3.93x lO mol/L-s. From the GPC molecular weight distribution curve reported for a 3% conversion sample, the weight fraction of polymer of DPn = 3000 is seen to be 1)7x10 . Calculate the weight fraction from Eq. (6.187) to compare with this value. [Use the following data C 0.02 Cm == 10 , fkd = 

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