Activation Energies and the Effect of Temperature

The influence of temperature on the course of a polymerization reaction depends on initiator efficiency and decomposition rate, chain transfer, and chain propagation, but it is important to have some knowledge of its effect in order to formulate optimum conditions for a reaction. 

The energy of activation of a polymerization reaction is easily determined using an Arrhenius plot when the rate constants have been determined at several temper-amres, but even for a simple reaction, the overall rate is still a three-stage process, and the total activation energy is the sum of the three appropriate contributions for initiation, propagation, and termination. 

Remembering that Vp is proportional to the overall activation energy 

The term (E -jE ) provides a measure of the energy required to polymerize a particular monomer and has been estimated for styrene to be 27.2 kJ mop and for vinyl acetate, 19.7 kJ mol . Initiators have values of E in the range 125 to 170 kJ mol , and this highlights the controUing role of the initiahon step in free-radical polymeriza-don. Consequently, values of E are generally in the range 85 to 150 kJ mol . 

As the temperamre term in the rate equation is exp E -- E - E )IRT, the exponent wih normally be negative so that the polymerization rate will increase as the temperatore is raised. The change in molar mass can also be examined in this 

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Explain the importance of activation energy and the effect of temperature on the rate constant (Arrhenius equation) ( 16.5) (SP... 

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