Double glass transitions in exfoliated poly(methyl methacrylate)/organically modified MgAl layered double hydroxide nanocomposites

Abstract

A series of nanocomposites based on poly(methyl methacrylate) (PMMA) and organically modified MgAl layered double hydroxides (O-LDH) were synthesized via in situ polymerization. The modification of LDH by sodium dodecylbenzenesulfonate (SDBS) resulted in an enlarged interlayer distance and a nearly complete substitution of the original NO₃⁻ in LDH layers. The polymerization of methyl methacrylate led to a disorderly exfoliated LDH in the PMMA matrix. The results of dynamic mechanical analysis (DMA) showed that there were two tan δ peaks in the PMMA/O-LDH nanocomposites at low frequencies. And the second peak at about 80 °C higher than the main peak (glass transition of PMMA matrix) gradually disappeared with increasing frequency, corresponding to the glass transition of PMMA chains confined on the O-LDH surface. Both of the two peaks shifted to higher temperature with increasing heating rate due to the strain lag of the sample.