Polymerisation of vinyl chloride initiated by the tri‐<i>n</i>‐butylborane‐oxygen system

Abstract

Abstract The bulk polymerization of vinyl chloride was studied kinetically at 25°C. using the Bu 3 B/O 2 system as initiator. The dilatometric conversion‐time curves show an autocatalytic behaviour and a discontinuity in the 4–8% conversion range at which a coagulation of the polymer particles occurs. The Bu 3 B reaction order was 0.56. This value, slightly higher than the theorically expected 0.5, is explicable by the occlusion of the chain radicals in the precipitated polymer. The apparent activation energy was obtained from a set of polymerizations carried out at different temperatures and resulted to be 9.6 kcal/mole. From this value the initiation activation energy was calculated to be 16 kcal/mole. A number of polymerizations were carried out in the temperature range +25 to −78°C. The average molecular weights of the products firstly increase and then decrease with increasing polymerization temperature, passing through a maximum at about −30°C.