Modified IPDA

If the complex (or chelate) concentration within the Hquid amine or epoxyamine prepolymer was higher than its solubihty Hmit, complexes (or chelates) crystallized. Sharp needle-like crystals were observed with modified IPDA what- 

---

Fig. 7.3 Series of POM images showing evolution during a DGEBA/AI-modified IPDA curing cycle.

In previous studies [3, 4], we had pointed out that the interphase formation mechanisms result from dissolution of the metallic surface layers, concomitantly with ion diffusion through the liquid prepolymer. In order to detect the dissolution phenomenon, pure amine (either DETA or IPDA) was previously applied to chemically etched metallic sheets (either A1 or Ti alloys were used, and had hydroxidic surfaces). After 3 h, the metallic surfaces were scraped with a PTFE spatula. The modified amine (i.e., the amine reacted with the metal) was analyzed. Whatever the natures of the amine and the metal were, metal ions were detected in the modified amines by ICP analysis and new peaks were detected by infrared spectroscopy [5]. To indicate hydroxide dissolution, a very thin layer of liquid amine was applied to chemically etched aluminum, and Infrared Reflection - Absorption Spectroscopy (IRRAS) spectra were recorded every 5 min (the hydroxide band intensity variation at ca. 3430 cm was followed). The OH group peak intensity decreased when the amine-metal contact time increased [5]. Conversely, if pure DGEBA monomer was apphed to the metal surfaces, even after 3 h in contact with the metallic surfaces, no metal ion was detected by ICP in the DGEBA recovered, and the infrared spectra remained identical before and after the contact with the metal. Finally, if pure amine monomer was applied to gold-coated substrates, no chemical reaction was observed (by either IGP or FTIR analyses). 

Finally, the variation of the glass transition temperature for both systems (DGEBA-IPDA or DGEBA-DETA) versus the stoichiometric ratio (a/e) is reported (e.g., see Fig. 7.6) for either pure or modified materials. Usually, as the functionalities of epoxy and amine monomer were well defined, mixing materials at the stoichiometric ratio of 1 led to the formation of the most crosslinked network having the highest glass transition temperature. From Fig. 7.6 it can be... 

---