Structural effect of phenalkamines on adhesive viscoelastic and thermal properties of epoxy networks

Phenalkamine, the Mannich reaction products from cardanol, formaldehyde, and polyamines were prepared using ethylene diamine, diethylene triamine and triethlene tetraamine. These products were characterized by high-pressure liquid chromatography (HPLC), infrared spectroscopy, and nuclear magnetic resonance spectroscopy (1H NMR). Clearly resolved peaks due to presence of triene, diene, monoene, and saturated side chain containing species of cardanol were observed in HPLC. The presence of characteristic methylene linkages of Mannich bases at delta 3.5-4.0 ppm was observed by 1H NMR. These curing agents were reacted with diglycidyl ether of bisphenol-A at room temperature and the curing times were optimized. The cured resins showed good adhesion with different metal surfaces particularly higher values were observed with copper due to its high surface energy. The viscoelastic properties of the cured samples were determined by dynamic mechanical thermal analysis. The storage modulus (E ') was found to be in the order of 10(9) Pa and tan delta values are around 90 degrees C. A reduction in storage modulus (E ') and an increase in tan delta values on postcuring were observed. Thermogravimetry analysis showed two-stage degradation above 250 degrees C for the cured samples. (c) 2006 Wiley Periodicals, Inc.