Bulk Polymerization of Vinyl Chloride: Nucleation Phase

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Abstract
Techniques are presented to follow the formation of the first polymer structures. The instrumentation is based on the use of a turbidimetric device equipped with a 1-liter glass autoclave and special sampling procedures. First particles appear as conversion reaches a value of approximately 10–5; they are spherical at 50 or 60°C, but somewhat more complex at lower temperatures. Their number, related with the free radical formation rate, remains constant up to a critical conversion rate, which depends strongly on stirring speed. Above this critical rate, a second nucleation begins and simultaneously the submicronic primary particles (“granules”) agglutinate to form “grains,” the size of which is not lower than 20-30 Mm. Some kinetic data, as well as molecular characteristics, are indicated.

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