Internal antiplasticization in diglycidyl ether of bisphenol A diamino diphenyl methane non‐stoichiometric epoxy networks

Abstract

DGEBA‐DDM (diglycicyl ether of bisphenol‐A‐diamino diphenyl methane) networks of various epoxide/amine molar ratios ranging from 0.7 to 1.4, were studied by density, quasi static (10−4 s−1), and ultrasonic (5 106 s−1) modulus, and thermostimulated creep measurements. Any step aside stoichiometry leads to an antiplasticization, e.g. an increase of the quasi static modulus, whereas Tg decreases. The previous interpretations (based on volumetric property considerations), of this phenomenon are questionable. The only common feature of all the antiplasticized systems is an unexplained decrease of the population of macro‐molecular segments involved in beta motions.

Dependence of dynamic mechanical behavior of DGEBA/DDM stoichiometric epoxy systems on the conditions of curing process

“…The variation of that property was also evident at low temperatures for all samples. A clear decreasing of modulus at the -P-relaxation zone happened for all schedules, indicating the usefulness of that relaxation in explaining variations of the stiffness of epoxy networks a t temperatures higher than those of the @-relaxation peak?.8s9.33 Indeed, as has been shown for non-stoichiometric epoxy systems, 9,27 higher values of elastic modulus for low crosslinked systems can be expected a t room temperature as a consequence of a lower magnitude of the P-relaxation. Instead, in the wtransition region solely, the networks which showed this relaxation had an evident decreasing of the modulus throughout the transition, also indicating the significance of w-relaxation on viscoelastic properties.…”

Structure and properties of amine‐hardened epoxy/benzoxazine hybrids: Effect of epoxy resin functionality

“…This is usually accompanied with decreasing intensity of the β‐relaxation process and reduction of the loss modulus in this region 25, 27. The phenomenon, termed ”internal antiplasticization,“ is also known for thermosets and it was observed for example in nonstoichiometric or partially reacted EPs 19, 29. Internal antiplasticization is usually accompanied with decreasing storage modulus in the temperature range of β‐relaxation, enhanced storage modulus in the region between β‐ and α‐transitions, and reduced T g .…”

“…This is because of many factors that should be taken into account during interpretation. For example, size of relaxing groups,28 size and position of substituents, stereochemical microstructures, stoichiometry,29–31 curing procedure,32 hydrothermal and physical ageing,33, 34 additives (either plasticizers or antiplasticizers),25–27, 35 etc. can influence the position and intensity of β‐relaxation.…”

Effect of epoxy–amine stoichiometry on cured resin material properties

“…Bellenger et a1. 16 have reported a decrease in the intensity of the loss peak associated with the p transition for the DGEBA-DDM system cured with nonstoichiometric quantities of amine compared to the system cured at the stoichiometric point. This corroborates the view that a decrease in segmental mobility causes an increase in modulus.…”