Thermoset epoxy-clay nanocomposites: The dual role of α,ω-diamines as clay surface modifiers and polymer curing agents

Diprotonated forms of polyoxypropylene diamines of the type α,ω-[NH₃CHCH₃CH₂(OCH ₂CHCH₃)_xNH₃]²⁺ with x = 2.6, 5.6, and 33.1, have been intercalated into montmorillonite and fluorohectorite clays and subsequently evaluated for the formation of glassy epoxy-clay nanocomposites. The intercalated onium ions functioned concomitantly as a clay surface modifier, intragallery polymerization catalyst, and curing agent. Depending on the chain length of the diamine, different orientations of the propylene oxide chains were adopted in the clay galleries, resulting in basal spacings from ∼ 14 Å (lateral monolayer, x = 2.6) to ∼ 45 Å (folded structure, x = 33.1). The initial clay basal spacings were correlated with the formation of intercalated and exfoliated clay-epoxy nanocomposites with improved mechanical properties and high thermal stabilities. In comparison to clay-monoamine intercalates, the use of diamine intercalates greatly reduced the plasticizing effect of the alkyl chains on the polymer matrix, resulting in improved mechanical properties while at the same time reducing the cost and time needed for nanocomposite fabrication.