Shape memory polymers from benzoxazine-modified epoxy

Abstract

Shape memory properties of specimens consisted of aromatic epoxy (E), aliphatic epoxy (N), Jeffamine D230 (D) and BA-a benzoxazine monomer (B) were evaluated. The mole ratio of D/B = 1/0, 0.8/0.2, 0.6/0.4, 0.4/0.6, 0.2/0.8 and 0/1 were used as a mixed curing agent for epoxy system with a fixed E/N mole ratio of 1/1. Effects of BA-a content on thermal, mechanical and shape memory properties of epoxy-based shape memory polymers (SMPs) were investigated by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), flexural test and shape recovery test. The results revealed that the obtained SMPs exhibited a higher flexural strength and flexural modulus than those of the unmodified epoxy-based SMP at room temperature and at 20℃ above glass transition temperature (T[subscript g]). The presence of 1 mole BA-a as a curing agent provided the specimen with the highest T[subscript g])., i.e. about 72℃ higher than that of epoxy-based SMP cured by Jeffamine D230. The results of the shape-memory tests suggested that the obtained SMPs showed outstanding shape recovery and shape fixity performances with an addition of the BA-a. All SMP samples needed only a few minutes to fully recover to their original shape. The samples exhibited high shape fixity (98-99%) and shape recovery ratio (90-100%) which increased with increasing recovery temperature. In addition, recovery stress values increased with increasing BA-a mole ratio from 20 kPa to 38 kPa, when BA-a up to 1 mole ratio was added. All of the SMP samples fully recovered to their original shape at the end of 100 cycles with minimum change on their flexural strength.