Thermodynamics of polymerization.

I. THE CHILING TEMPERATURE CONCEPT A. Thermodynamic Approach The Gibbs free energy of a system at temperature T is defined as were H is the enthalpy and S the entropy of the system. The free energy change for any polymerization will be, therefore, When the polymer has a lower free energy than the initial monomer, a polymerization can occur spontaneously, and the sign of ΔG is negative. A positive sign for ΔG signifies, therefore, that the polymerization is not spontaneous. When the system is in equilibrium at a certain critical temperature, there is no tendency for polymerization, and, hence, ΔG = 0 [1–3]. This temperature is known as the ceiling temperature. These three possible conditions for free energy change of polymerization may be summarized as follows: At the ceiling temperature, Tc, ΔG is zero, so that where ΔHp and ΔSp are the enthalpy and entropy changes per monomer unit.