Fig. 2: Tg comparison applications where the retention of mechanical properties in hot and wet conditions is critical. This resin melts at medium temperature (η: 1000-1500 mPa.s @ 85°C) and is easily compatible and processed with other epoxy resins. Liquid epoxy resins with high thermal performances and high modulus Fig. 4 : TGPAP and TGMAP chemical structures Fig. 5 : Higher modulus with TGMAP Fig. 3: Ultimate Tg and water absorption When prepreg formulators think high end performances they often think TGMDA (tetraglycidylether of methylene dianiline) or TGPAP (triglycidylether of para-aminopheno) l. The best known and most proven members of those families of multifunctional epoxy resins are Araldite® MY721, a viscous tetra-functional resin (η: 4000 - 6000 mPa.s @ 50°C) and Araldite® MY0510 , an extremely fluid tri-functional resin (η: 600- 800 mPa.s @ 25°C) that is unique in its capability to dissolve thermoplastics such as polyethersulfones (PES), key ingredients of toughened prepregs. Both resins are characterized by their ease of processing and high cross-linking density of their cured networks. Huntsman recently introduced the triglycidylethers of meta-aminophenol (TGMAP) family of which Araldite® MY 0610 is the most recent product, already qualified for very critical and high end applications. In comparison to TGPAP molecules where the epoxydized hydroxyl group is in the “para” position, a simple change of this group to the “meta” position (figure 4) has very important consequences: TGMAP molecules provide networks with significantly higher modulus than TGPAP (and TGMDA) without drastic decrease in thermal resistance (figures 5). It has also been shown that this asymmetrical structure plays a positive role in the toughness of the cured resin. High thermal performance and reduction brittleness in epoxy networks One way to improve the toughness of thermoset networks is to decrease their cross-linking density, but this is very often it is at the expense of their rigidity Fig. 6: Araldite® MY 0816 No79 March 2013 / jec composites magazine 101