Pairs of sterically hindered and unhindered linear aliphatic and aromatic diamines were synthesized and used as curatives for the diglycidyl ether of bisphenol A (DGEBA). The steric hindrance was caused by methyl group substitution of a hydrogen atom adjacent to the amine. For each pair, the hindered diamine cure had a lower density and a higher glass transition. Another pair of diamines was synthesized for which the methyl group was replaced by ethyl and butyl side chains; for these resins, both the density and glass transition decreased. Torsional pendulum results show that the sub-glass transition for the hindered cures shifts to lower temperatures and has a greater activation energy. Analysis by the Havriliak-Negami dispersion equation shows that the hindered resins have broader and more symmetrical relaxations. The background hysteresis loss outside of the relaxation region was analysed by the Nutting equation and was found to decrease with steric hindrance
Посилання на статтю:
The effects of steric hindrance on sub-glass transitions in epoxy polymers / Edward Balizer* and James V. Duffy // Polymer. – 1992. – Vol 33. – P. 2114-2122.