Thermodynamics of cationic polymerization

Sawada [406] described the thermodynamics of cationic polymerization as follows The process of protonic acid initiation of cationic polymerization starts with heterolytic bond dissociation of the acid. The energy of this process can be designated by the quantity C2, the affinity of the proton for the olefin. The potential energy between ion pairs separated at a distance r is 

By substituting the above values, the free energy change of initiation, can be written as 

The entropy change and the enthalpy change are negative for the free energy change to be negative. 

In the propagation process, the change in activation entropy is based on two phenomena (a) the entropy change of immobilization of a free-moving monomer into a polymeric chain and (b) the difference of entropy in the solvation between the reactants and the transition state, which can be written as 

AS solvation is a positive term because in the transition state the electric charge is more diffuse and the degree of solvation is lower than that of the more compact dipolar species corresponding to reactants. 

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