Thermal-oxidation of epoxy/amine followed by glass transition temperature changes

Abstract

Thermal oxidation of three epoxy resins differing by the nature of prepolymer (bisphenol A diglycidyl ether and 1,4-butanediol diglycidyl ether) and hardener (isophorone diamine and 4,7,10-Trioxa-1,13tridecanediamine) was studied by monitoring changes in glass transition temperature using DSC. Results were discussed using the DiMarzio's approach in which parameters are estimated from an additive group contribution. This theory allowed a fair assessment of T g values for unaged networks. During oxidation, epoxy networks were shown to undergo chain scissions occurring in great part in hydroxypropyl ether and isophorone groups. However, the exploitation of T g changes showed the coexistence and even the predominance of crosslinking in materials having linear aliphatic segments. The DiMarzio's approach was used to discuss the possibility of intramolecular cyclization or intermolecular crosslinks which were shown to predominate. Crosslinks were tentatively justified from a mechanistic point of view and quantified depending on experimental conditions.

Thermal oxidation of aromatic epoxy-diamine networks

“…Thermal oxidation of epoxies is documented to induce chain scissions [1,2] and later volatile compounds [3,4]. The subsequent mass loss results in the appearance of cracks favoring the access of oxygen to deeper layers [5].…”

“…Another difficulty is linked to the structural complexity of epoxy-diamine networks family, which is actually constituted by a wide number of prepolymer hardener pairs, where several sites are likely to participate to the oxidation process [9e11]. The glass transition of networks ranges from less than 100 C to more than 200 C [2,12,13] so that a supplementary level of complexity linked to the effect of macromolecular mobility might complicate the comparison of data obtained in glassy state or rubbery one.…”

Origin of epoxies embrittlement during oxidative ageing

“…For this purpose, we have chosen three epoxy networks: two systems having a relatively low T g (DGEBA/TTDA and DGEBU/IPDA, 69 and 60 C respectively) and a system having a high T g (DGEBA/IPDA, 166 C). Furthermore, it has been witnessed that among these systems, one system undergoes mainly chain scission (DGEBA/ IPDA) whereas the other undergoes mainly crosslinking [12]. The final objective is then to propose a common scenario to explain embrittlement induced by oxidation for epoxy networks.…”

Preparation of 4‐(4‐hydroxyphenoxy)phenol diglycidyl ether with improved toughness behavior

“…The first rapid degradation started from circa 320 °C and the T max values were between 364 and 377 °C. This stage could be assigned to the cleavage of ether bond and the dehydration process of secondary alcohol in the polymer network . The second stage attributed to the thermo‐oxidative degradation of chemical entity, and the formation of sufficiently low molecular weight and volatile fraction .…”

“…This stage could be assigned to the cleavage of ether bond and the dehydration process of secondary alcohol in the polymer network. [39][40][41] The second stage attributed to the thermo-oxidative degradation of chemical entity, and the formation of sufficiently low molecular weight and volatile fraction. 42 Under inert environment, it appeared that only the first step of degradation behavior occurred [ Figure 9(a)].…”