Controlling static and dynamic properties of imine vitrimer networks by changing epoxy amine stoichiometry

This study investigates the effect of epoxy amine stoichiometry on the static properties and dynamic behaviour of a para substituted epoxy imine vitrimer ( p VAPI). The p VAPI is synthesised and cured with diethyltoluene diamine (DETDA) over a range of stoichiometries from epoxide to amine excess. The imine group catalyses chain growth polymerisation, establishing a dual curing mechanism consisting of homopolymerisation and epoxy amine addition. Increasing amine content reduces the glass transition temperature ( T g ), increases modulus and strength, while leaving strain to failure largely unaffected. The thermal stability and thermomechanical behaviour were not greatly impacted. The p VAPI vitrimer networks display the greatest dynamic behaviour at stoichiometric extremes, amine and epoxide excess, while balanced stoichiometric formulations exhibit the least. In the case of amine excess, transimination is identified as the most likely source of dynamic behaviour, while in the case of the epoxide excess networks, the low T g and heterogenous nature of the epoxy network is considered most likely origin. For these networks, stress relaxation is fastest, and malleability and creep the highest. In the case of weldability, amine excess provided the greatest polymer chain diffusion across network interfaces which is attributed to transimination across disconnected softened interfaces.