Effect of Vitrification on the Polymerization Rate

When vitrification sets in, there is an overall diffusion control that affects the rate of both stepwise and chainwise polymerizations, because segmental motions are considerably slowed down. 

Let us analyze a particular example where the influence of vitrification on polymerization rate has been clearly established. Wisanrakkit and Gillham (1990) reported the polymerization kinetics for a diepoxide (DGEBA) reacted with a stoichiometric amount of an aromatic diamine (trimethylene glycol di-p-aminobenzoate, TMAB). The reaction rate, measured outside the vitrification region, could be expressed by the following equations  

Equation (5.44) constitutes a particular case where Eq. (5.2) holds. Integrating the generic Eq. (5.2) at constant temperature and taking natural logarithms, leads to 

As discussed in Chapter 4, for many thermosetting polymers a unique relationship may be established between conversion and glass transition temperature, as was also verified for this particular diepoxide-diamine system (Wisanrakkit and Gillham, 1990). So, the left-hand side of Eq. (5.46) may be written as a unique function of Tg, F(Tg) 

With the aid of Eq. (5.47), experimental Tg vs t curves obtained at different cure temperatures may be horizontally shifted to obtain a master curve. Equation (5.47) may be written for a reference temperature, T  

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