INDEX precipitation experiments

Experiments conducted with dimethylformamide solutions at 20°C have shown that the "auto-acceleration index" 3 indeed decreases upon dilution and becomes 1.0 in a 40 per cent monomer solution where the polymer still precipitates (18). The data are summarized in Table II. 

A sample of the suspension can then be taken and titrated separately with a double beam spectrophotometer, the reference being the initial solution. The optical density of the solution at X = 650 mn is actually proportional to the amount of S produced in the experiment. This was checked by a gravimetric titration of the precipitate which served as a standard for the optical method. The experience was repeated at all the injection points indexed on Figures 2 and 3. The amount of precipitate is simply additive from one experiment to the next. These amounts (Cg = 10- to 10 2 moles. m 3 per experiment) are very small as compared to the concentration of reactants. CQ can thence be identified to (Ba +)0 and it is not necessary to readjust the reactant concentration as long as the number of sucessive injections does not exceed about ten. It can be noticed from [4] that precipitation is facilitated by the presence of pre-existing precipitate. 

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