Mechanistic study of thermal behaviour and combustion performance of epoxy resins. II. TGDDM/DDS system

Abstract

The kinetics of curing of tetraglycidyl 4,4′-diaminodiphenylmethane (TGDDM) with 50% or 85% of stoichiometric 4,4′-diaminodiphenylsulfone (DDS) was studied by differential scanning calorimetry. It was found that the activation energy of the process increases with advancement of curing, which is caused by concomitant homopolymerisation of TGDDM accompanied by cyclisation. The structure of the cured formulations was characterised by infrared and 13C NMR spectroscopy. The mechanistic study of thermal decomposition of TGDDM/DDS systems was carried out by thermogravimetry and differential scanning calorimetry in inert atmosphere and by thermal volatilisation analysis in vacuo. It was found that above 200 °C elimination of water from secondary alcohol groups takes place with formation of aliphatic unsaturation. Breaking of the resulting weakened allylic CN bonds leads to chain scission with formation of primary amine and quinolin-type chain ends. Scission of non-allylic CN bonds followed by evolution of acetone was observed at about 300 °C. The volatilisation of sulfur-containing species and formation of a thermostable char occurred on further heating to 400 °C. The poorer fire resistance of TGDDM/DDS formulations in comparison with homopolymerised TGDDM is discussed on the basis of a lower yield of char and a higher yield of gases.