Low temperature cure of epoxy thermosets attaining highTgusing a uniform microwave field

ABSTRACTIt is demonstrated for the first time that an epoxy thermoset resin can be cured at temperatures well below itsTg∞. This study compared the use of a uniform variable frequency microwave (VFM) field to standard oven curing at temperatures above and belowTg∞. UsingTg, tan δ, modulus, and FTIR measurements, it is shown that the reaction of BFDGE with MDA to attain a product withTg∞of 133 °C is achieved by VFM at temperatures from 100 to 140 °C; in contrast, the thermal cure normally requires 170 °C to attain the sameTg∞and the same extent of cure. By following the pregel cure reaction with13C‐NMR spectroscopy, it was determined that the lower cure temperatures of VFM cure predominately lead to chain extension and smaller amounts of crosslinking compared to the thermal cure. To explain these results, it is suggested that, after gelation, with VFM cure there is higher mobility from dipole rotations that continues the cure to completion without vitrification. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci.2016,133, 44222.