Gelation Theory Versus Experiment

Note that % is not very large, nor is it increasing rapidly at the gel point. This means that the proportion of large molecules present at this stage is small, but profoundly affects the viscosity. FIGURE 5-22 Rory s experimental recipe. 

FIGURE 5-23 Flory s experimental results [replotted from the data of P. J. Rory. Principles of Polymer Chemistry, Cornell University Press (1953)]. 

Note that all the OH groups on pentaerythritol are equivalent, so their reactivity is the same. Because this molecule has a functionality/- 4, the theoretical value of a. = 0.333, corresponding to a critical value of p, pc = 0.577 (remember p is the fraction of groups that have reacted and in these experiments p pA = p. Experimentally, the gel point occurred atp- 0.63. These authors then went a step further, arguing that the probability of intramolecular condensation would increase 

Advancing Fronts in Chemistry, S. B. Twiss Ed.. Reinhold, New York, 1945. 

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