Depropagation during Copolymerization

In contrast to the kinetic approach, deviations from the terminal model have also been treated from a thermodynamic viewpoint [Kruger et al., 1987 Lowry, 1960 Palmer et al., 2000, 2001]. Altered copolymer compositions in certain copolymerizations are accounted for in this treatment in terms of the tendency of one of the monomers (M2) to depropagate. An essential difference between the kinetic and thermodynamic treatments is that the latter implies that the copolymer composition can vary with the concentrations of the monomers. If the concentration of monomer M2 falls below its equilibrium value [M]c at the particular reaction temperature, terminal M2 units will be prone to depropagate. The result would be a 

In case II, M2 tends to depropagate only when it is attached to a sequence of two or more M2 units  

Thus MiM does not depropagate in case I, while neither - MiM2 nor MiM2M2 depropagate in case II. 

The copolymer composition for case I is given by [Kruger et al., 1987 Lowry, 1960 Szymanski, 1987] 

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