Inhibition of Radical-Initiated Polymerisation of Vinyl Acetate by Tobacco Smoke and Some Polycyclic Hydrocarbons

A wide range of organic compounds, which are capable of intercepting free-radical intermediates formed during radical-initiated vinyl-acetate polymerisation, have a marked impact on the rate of polymerisation of vinyl acetate. The efficiency with which a compound retards polymerisation can be estimated by measuring the time it takes 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. We have tested the efficiency of smokes from various sources as inhibitors as well as a range of polycyclic hydrocarbons. Smoke vapour is strongly inhibitory, and the activity has been attributed to conjugated dienes chiefly isoprene. Smoke condensates from different tobacco types can be differentiated by their relative efficiencies in retarding polymerisation. Flue-cured tobacco smoke has the highest activity; smoke from reconstituted tobacco has the lowest; air-cured, stem and perique tobacco have intermediate values. The effect of the smoking vehicle was measured by testing cigar and pipe-smoke condensates. The former has a value similar to air-cured tobacco but the latter has a very low activity. Of the polycyclics which we scanned, carcinogenic substances generally showed higher activities than non- carcinogens. Some weak carcinogens such as anthracene were, however, unexpectedly active inhibitors. A polyaromatic-hydrocarbon-enriched fraction of smoke did not appear any more active than a crude condensate. The mechanisms by which smoke inhibits polymerisation are discussed. All three possible mechanisms - substitution reactions, atom transfer and radical coupling - probably occur. It is not possible at this point to suggest which is the dominant one.