Temperature Effects in Radical Polymerization

In the initial stages of polymerization, the temperature dependenee of the rate constants in Eq. (5.3.14) can be expressed through the Arrhenius law  

This representation is completely parallel to the temperature dependence of rate constants for reactions of small molecules, isj, Ep, and are, therefore, the activation energies for initiation, propagation, and termination reactions, respectively. The values are tabulated extensively in the Polymer Handbook [4]. The temperature dependence of and can be easily found by substituting Eq. (5.7.1) in Eqs. (5.3.14) and (5.4.4) to get 

The activation energies are such that the overall polymerization for thermally dissociating initiators is exothermic (i.e., Ep — 0.5 4- 0.5isi) is normally positive, so the rate increases with temperature. On the other hand, Ep — ).5Et — 0.5 i is usually negative for such cases and /r decreases with increasing temperature. 

After the gel point sets in, the temperature dependence of kp and is as follows [14]  

The terms Egp and Eg are parameters to be determined from the data on gel effeet. 

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