Intercalation of poly(propyleneoxide) amines (Jeffamines) in synthetic layered silicas derived from ilerite, magadiite, and kenyaite

Abstract

The synthetic layered silicates Na⁺-ilerite (Na₂Si₈O₁₇·nH2O), Na⁺-magadiite (Na₂Si₁₄O₂₉·nH₂O), and K⁺-kenyaite (K₂Si₂₀O₄₁·nH₂O) were converted to the corresponding layered silicic acids (silicas) through the stoichiometric replacement of the gallery alkali metal ions with protons. The protonated derivatives were subsequently used as hosts for the intercalation of poly(propyleneoxide) amines that are normally used as curing agents for thermoset polymers. The amines of interest were the commercially available α,ω-diamines known as Jeffamine D-series amines and Jeffamine T-series glycolitic triamines with molecular weights in the range 400–5000. Low molecular weight Jeffamines (MW∼400) intercalate in all three layered silicas as lateral monolayers in which the PPO chains are oriented parallel to the silica sheets and the gallery heights are restricted to values of 4.0–4.9 Å. Amines with MW values of 1000–5000 afford intercalates in which the gallery heights are 2.6–9.0 times as large as the thickness of the host layers and the PPO chains adopt coiled conformations in the galleries. Substantial de-intercalation of the high MW amines occurs upon mild extraction with ethanol–water mixtures, as expected for an intercalation mechanism that involves hydrogen bonding between the amine head groups and silanol groups on the basal surfaces of the host silicas. The ability to control the amine to silica ratios in these intercalates should prove to be advantageous in applying these materials for the preparation of epoxy-layered silicates nanocomposites and other thermoset nanocomposites derived from amine monomers.