Curing behaviour of epoxy resins with a diamine bearing an azobenzene group

Abstract

Abstract N,N-Diglycidylaniline (DGA) has been cured with the new chromophore 2,4-diamino-4'-methylazobenzene (DMAB). The curing kinetics of this aminophenyl epoxy resin/DMAB system was studied in isothermal experiments by means of differential scanning calorimetry. Autocatalytic behaviour is seen in the first stage of the cure and can be described by a model proposed by Kamal. The later stage is practically diffusion-controlled (beyond the glass transition). The diffusion effect is introduced into Kamal’s equation. Parameters such as rate constants and activation energies are calculated. Good agreement between calculations and experimental data is found. The curing kinetics of bifunctional DGA is compared with that of trifunctional N,N-diglycidyl-4-glycidyloxyaniline (DGOA) with the same tetrafunctional curing agent DMAB. The rate constants for DGA + DMBA are slightly higher than those for the DGOA + DMAB system. The activation energy for the former (E1 = 64.1 kJ/mol, E2 = 56.2 kJ/mol) is lower than for the latter system (E1 = 71.6 kJ/mol, E2 = 70.5 kJ/mol). DGA needs to be cured at a lower temperature than DGOA. The relationships between glass transition temperature, Tg, and rate of conversion and time of curing is discussed as well. DGA cured with DMAB exhibits a lower Tg (220°C) and thermal stability than DGOA + DMAB (Tg = 240°C) because of the lower functionality of the DGA resin. Preliminary investigations of optical grating recording in the new material were carried out. The presence of azobenzene groups in such epoxy systems enables their application as potential materials for holography.