Study of Thermo– and Photooxidation of Head-To-Tail and Head-to-Head Polystyrene Films

Abstract

Abstract A study was made on the thermo– and photooxidation of head-to-tail (PS) and head-to-head (H-HPS) polystyrene films. The process was followed by determination of the overall oxygen uptake (conversion), IR spectrum, molecular mass distribution, and carboxyl group concentration. The mechanism of the process depends on the type of initiation (thermal or photo). For either the thermally initiated or photoinitiated process, the mechanism depends very little on the structure of the polymer, but the oxidation of H-HPS is much faster. This can be ascribed to the higher concentration of structural defects (mainly double bonds) in H-HPS and not to the difference in the basic structure of the polymers. In thermal oxidation, at least three carbonyl groups with different structures, phenolic hydroxyl groups, and a small quantity of carboxyl groups could be detected. Plotting the carbonyl concentration against conversion resulted in a more or less linear function. The concentration of phenolic hydroxyl groups was found to increase slightly with oxygen pressure (p). Thus, the rate of oxidation slightly decreases with increasingp (more pronounced autoinhibition). The fragmentation taking place in thermal oxidation and the carbonyl formation are connected. Hydro-peroxide, carboxyl, and (mainly ester) carbonyl groups can be detected in photooxidation. Head-to-tail PS is fragmented very slightly in this process, while oxidized dimers and trimers are eliminated from H-HPS.