On the polymerization of vinyl acetate

The rate of thermal polymerization of vinyl acetate has been examined by Starkweather and Taylor (1930) and by Breitenbach and Raff (1936). Whilst the former obtained consistent unimolecular velocity constants except in toluene solutions where the 4 ‘ constants ” showed a progressive fall, the latter found that their results were not reproducible and believed that the reaction might be heterogeneous. Observations by Cuthbertson, Gee and Rideal (1937) led to the conclusion that both the velochy and extent of polymerization was associated with the presence of an aldehyde peroxide, since freshly prepared material, when aldehyde free, did not polymerize even when maintained at 100° C for 24 hr. In contact with air and moisture however, together with traces of alkali from the glass, slow hydrolysis occurs and subsequently the aldehyde formed, detected with Schiff’s reagent, combines with oxygen to form a peroxide catalyst, detected by ammonium thiocyanate and ferrous ammonium sulphate (Kharasch and Mayo 1933). Preliminary experiments by Wood (1935) and Campbell (1937) with packed vessels containing glass wool and glass chips revealed, apart from the effects of alkali on the hydrolysis, no evidence of a surface polymerization. In this communication an account is given of an attempt to establish the mechanism of the kinetics of the polymerization in the liquid phase. In order to mask the effects of possible traces of foreign catalysts in the monomer it was considered preferable to study the rate of the reaction catalysed by the addition of reasonable quantities of benzoyl peroxide. This procedure has the further advantage of enabling the rate of the initiation process to be controlled.