Curing of Diglycidyl Ether of Bisphenol P (DGEBP) with Nitro Derivatives of Amine Compounds

摘要

DSC, TGA, DMA, polarized lightmicroscopy (PLM) and advancedisoconversional kinetic analysis were used tostudy the curing reaction of diglycidyl etherof 4,4'-bisphenol P (DGEBP) epoxy resinwith aromatic amines,4-nitro-1,2-phenylenediamine (4-NPDA) and3-nitro-1,2-phenylenediamine (3-NPDA). ForDGEBP/4-NPDA system, the curing processis associated with the first exothermic peak onthe DSC curve. Kinetic analysis suggests thatthe effective activation energy for the curingprocess is ≈50 kJ mol-1. It is consistent withtypical values of activation energy ofepoxy-amine cure that are reported mostfrequently. The curing process is associatedwith the formation of a liquid crystallinephase that can be converted to anothermesophase on cooling if the system is notcompletely cured. The transition between thetwo mesophases becomes irreversible on further heating. For DGEBP/3-NPDA system, the curing reaction is characterized by two processesrepresented by the first two exothermic peaks on a DSC curve. Kinetic analysis suggests that theeffective activation energy for the first process is ≈50 kJ mol-1, and for the second process, is about 100kJ mol-1. The increase is explained by different reactivity of the two –NH2 groups that, in its turn,depends on their position with respect to –NO2. The –NH2 in position 2 is less reactive than that inposition 1 because the -H is highly congested and hindered from nucleophilic effects by electrostaticrepulsion of the -NO2 group. This effect creates an extra energy barrier to the curing reaction and leadsto the increase of activation energy of cure from 50 to constant 100 kJ mol-1. It is proved by curingDGEBP with an aromatic monoamine, 2, 4-dinitroaniline (2,4-DNA). For this reaction, kinetic analysisshows an activation energy around 110 kJ mol-1 which is similar to the activation energy in the secondstep of curing of DGEBP/3-NPDA system.