Thermal Degradation of Epoxy Resins
The thermal degradations of Bisphenol A-based epoxy resins cross-linked with diaminodiphe nylmethane or with phthalic anhydride were studied with the aid of pyrolysis and radiochemical gas chromatography technique [511]. The products of degradation depend upon the temperature. At 400C, the amine cross-linked resins yield hydrogen, methane, and water. The resins cross-linked with phthalic anhydride yield hydrogen, methane, carbon dioxide, and water. The number of degradation products increases with temperature. It was concluded that the most important nonscission reactions in these resins are competing with dehydration and dehydrogenation reactions [511]:
The scission reactions can take place at various weak spots. The breakdown of bisphenol A segments produces phenol [511]:
9.9 Thermal Degradation of Common Step-Growth Polymers
The main differences that were observed between amine-cured and anhydride-cured resins are [511]:
1. The amine cross-linked resin generated more water and hydrogen, because they contained more–CH2–CHOH–CH2– groups.
2. Scissions of anhydride-reacted resins tend to regenerate the anhydride and release CO and CO2 in large quantities
3. The aliphatic segments of the amine cross-linked resins yield more acetaldehyde than acetone. The reverse is true of the anhydride-cured resins. This is thought to be due to preferential rupture of carbon–nitrogen bonds [511]:
The anhydride-cured compositions may tend to break up symmetrically instead:
