TABLE OF CONTENTS The elimination process that occurs during the thermal degradation of poly(vinyl acetate) (PVAc) has been studied and it has been found that elimination of acetate groups initially begins slowly, but increases as degradation proceeds due to an additional process. The increase in rate was found to depend on the concentration of unsaturated groups in the polymer chain. The activation energy of the initial step was found to be 190 kJ/mol, while that for the additional process was 130 kJ/mol. The additional process of elimination was considered to be due to a four-membered transition state, activated by double bonds adjacent to the acetate unit {851392}. Scheme 23 shows the free-radical mechanism for PVAc thermal degradation [a.191].
Poly(isopropenyl acetate) (PIPA) is closely related to PVAc, the difference being that PVAc has the major part of its acetate groups attached to tertiary carbon atoms and only a small fraction of them attached to quaternary carbon atoms, whereas the acetate groups in PIPA are exclusively attached to quaternary carbon atoms. Unlike PVAc, PIPA degrades in two stages almost without residue. The first stage of degradation occurs between 150 and 250 C and consists of acetic acid loss, which corresponds to the maximum theoretical yield. At higher temperatures, the remaining methyl-substituted unsaturated backbone gradually breaks down, forming a mixture of aromatic hydrocarbons that make up a slightly volatile higher fraction and relatively...
