Amines stoichiometry

Fig. 12 Generalized block diagram of PGAA design structure and structures of the 16-polymer library of PGAAs. These polymers allow the direct comparison of changes in amine stoichiometry, as well as hydroxyl number and stereochemistry, on biological properties. Figure adapted with permission from [186], (C) 2006 John Wiley Sons, Inc...

Table 14.4 presents formulation information for bisphenol A and polyfunctional epoxy resin emulsions that are cured with an aliphatic amidoamine curing agent. Adhesive performance data are also provided for substrates common to the automotive industry. Both formulas are based on a 1 1 epoxy-amine stoichiometry and they are reduced to 45 percent nonvolatiles with water. The working life of each system is several hours at room temperature. 

The single limitation was that the acid chloride could not be present with free amine. When this combination occurred, either by addition of excess acid chlorides or by inadequate mixing so that localized excesses of acid chloride developed, an intense yellow color was produced which could not be dissipated by post reaction or by extraction. Other parameters examined for the sequential reaction included amine stoichiometry, temperature, hold terminal, and reagent purity. 

Amine Stoichiometry (Figure 7). It is necessary that a slight excess of amine be employed to achieve high molecular weight. The reasons for this are not at all clear. [A referee suggests this requirement for excess amine may reflect the effect of dissolved TEA HC1 on the polymerization. It may well be that the ionization of phenolic hydroxyls, viz., [—OH] + [TEA] = [—O"] + [TEA H+] is repressed by the increasing TEA.HCl concentration. Additional TEA would be expected to overcome this effect.]... 

Table III - Data for 1.0 2.0 epoxy-amine stoichiometry. Initial hydroxyl concentration...

Figure 11. Effect of initial epoxy amine stoichiometries on the fractional consumption of epoxy (O) 1.0 1.0, epoxy amine 1.0 2.0, epoxy amine 1.0 3.0,...

Amine stoichiometry was kept at 95% based on prepolymer content. Except where noted, prepolymers were preheated at 93°C and mixed with curatives at desired temperature. The prepolymer, curative and prepolymer-curative mixture were each vacuum degassed prior to pouring the mixture into a preheated mold. Degassing before and after mixing is especially important to achieve optimum cures. The mold was closed when gelation started. Demolding time was one hour or less. The sample was then post-cured for 16 hours at 120°C. The elastomer was conditioned for one week at 50% relative humidity at room temperature prior to physical properties measurement. 

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