Temperature and conversion effects

Temperature dependence. If the pertaining reaction constants can be described by the Arrhenius equation with E = energy of activation, then it follows from Equations 2.10 and 2.12, respectively that  

Radical polymerisations are often characterised by a sudden increase of Rp when a certain conversion is reached. The higher the initial concentration [M], the earlier this effect occurs. 

During the gel effect, steady state in radicals is no longer valid the radical concentration will increase. This means that substituting Equation 2.9 for the radical concentration 

With the occurrence of the gel effect both J p and P are higher than predicted. Although the great increase in heat production with increasing viscosity can be dangerous with respect to reaction runaway, in practice, proper use can be made of the gel effect. 

Induction period. In many cases the reaction does not start immediately but after minutes or sometimes even hours. This induction period is caused by preferential reaction of radicals with impurities in the reaction mixture, for example, oxygen. If the radicals reacted with all the impurities, the normal polymerisation reaction starts. Sometimes both the reaction with impurities and the normal polymerisation reaction proceed simultaneously in that case there is a retardation effect (slower overall polymerisation rate). 

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