Amine/epoxy reaction

In adhesive formulations, aliphatic amines are most commonly used to cure the DGEBA type of epoxy resin. Aliphatic amines are not widely used with the non-glycidyl ether resins, since the amine-epoxy reaction is slow at low temperatures. The reaction usually requires heat and accelerators for an acceptable rate of cure. Aliphatic amines are primarily used with lower-viscosity DGEBA resins because of the difficulty in mixing such low-viscosity curing agents with the more viscous epoxy resins. 

Instrumental analytical methods including HPLC, NMR and FT-IR have enabled the course of the reaction to be delineated by analysing the sol and gel fractions over time. In Section 1.2.1 the individual amine-epoxy reactions were presented, since the first stage of the reaction with a primary amine involves chain extension. This reaction competes with crosslinking since the reaction of the primary amine with epoxide is much faster than the reaction of the secondary amine. It is the latter reaction that results in branching of the chain and thus the formation of the first crosslinks. 

Several epoxy formulations are cured by both step-growth and chain-growth polymerizations occurring sequentially or in parallel. For example, BF3 complexes or tertiary amines may be added as catalysts of an amine-epoxy reaction, leading to different reaction mechanisms taking place whose relative significance depends on the cure temperature (or thermal cycle) and the initial stoichiometry. The structure and properties of the resulting polymer networks depend on the relative contribution of both mechanisms. 

Riccardi, C.C. Williams, R.J.J. (1986). A kinetic scheme for an amine-epoxy reaction with simultaneous. Journal of Applied Polymer Science, Vol.32, No.2, (August 1986), pp. 3445-3456, ISSN 0024-9297. 

DSC thermograms for the uncured epoxies are shown in Figure 3. The uncatalyzed system exhibits two reaction peaks, as observed in our earlier work (12). The lower temperature shoulder is attributable to amine-epoxy reaction and the higher temperature peak is due to hydroxyl and homopolymerization reactions. The... 

Additives containing the phenol group accelerate many amine-epoxy reactions and phenol is often added to amine curatives such as the aromatic amines. Such mixtures sometimes have an objectionable pungent odor and are quite corrosive to the skin. Other accelerators include furfuryl alcohol and salts specific to each type of amine. 

The initial increase in the heat capacity signal corresponds to the reaction heat capacity or the change in heat capacity from reactants to products (see arrow in Rg. 2.112). A thermodynamic analysis of the epoxy-aromatic amine reaction revealed that the primary amine-epoxy reaction contributes less to the increase in reaction heat capacity than does the secondary epoxy-amine reaction (Swier and van Mele 2003b). Information specific to the different steps in the reaction mechanism can therefore be deduced from the heat capacity signal, in contrast to the global conversion evolution obtained from the total heat flow signal. 

Fig. 4.21 Mosaic of rough superhydrophobic surfaces prepared by different techniques (a) PECVD, (b) electropolymerization, (c) grafting by amine-epoxy reaction, (d) electrospinning, (e)...

---