Inhibition of Radical-Initiated Vinyl Acetate Polymerisation by Tobacco Smoke Fractions

Both the vapour and particulate phases of tobacco smoke have been shown to retard benzoyI-peroxide-initiated polymerisation of vinyl acetate by interception of the radicals involved in the polymerisation process. The extent of inhibition of polymerisation by test compounds is estimated by measuring time taken for a mixture of monomer and benzoyl peroxide, immersed in a water-bath at 70°C, to reach a spontaneous boil and comparing it with the time required for a similar mixture with added retarder to reach boiling point. Units are expressed as minutes of inhibition per part per million of inhibitor × 10³. Inhibition by the vapour phase can be attributed to conjugated unsaturated compounds, chiefly isoprene which has an inhibition factor of 788 min. ppm^-1 × 10³ respectively. To trace the groups of compounds responsible for the inhibitory activity of the particulate phase, the particulate matter was fractionated by the method of Stedman et al. The fractions containing the highest activities were ether-soluble weak acids, methanol-soluble neutrals and nitromethane-soluble neutrals with inhibition factors of 83, 122 and 135 min. ppm^-1 × 10³ respectively. Since the nitromethane fraction contains most of the aromatic hydrocarbons produced on smoking and some polyaromatics are known to have high inhibition factors, it was subfractionated after the method of Grimmer but no subfraction with activity appreciably higher than the crude nitromethane fraction was obtained. The distribution of activity in the major fractions of the particulate phase of the smoke from a number of different tobacco types and smoking vehicles has been examined. These results and the mechanism by which smoke inhibits polymerisation are discussed.