| Abstract: | Thermogravimetric analysis (TGA) has been used extensively to determine the thermal stability of polymers. The present study indicates that the isothermal decomposition of polybutadienes (PBDs) is significantly different from that in the heat mode. The isothermal decomposition of PBDs is an exothermic reaction occurring at 350°–375°C. This decomposition is shown to be rapid and temperature specific. It appears to be related to the cyclization reaction reported previously by several investigators. Decomposition of PBDs in the heat mode (10°C/min) occurs at 447°–461°C. This is about 100°C higher than that observed in the isothermal mode. Further TGA experiments indicate that a period of slow heating stabilizes PBD and can eliminate the exothermic decomposition at about 360°C. This stabilization appears to be related to the ease with which both 1,2- and 1,4-PBDs thermally crosslink. Heating 1,4-PBD for 6 min at 270°C gives rise to 92% gel. 1,2-PBD is shown to crosslink more extensively. It is shown that polymers which do not thermally crosslink or cyclize, such as polystyrene, decompose similarly in the two modes of heating. |
