Structural studies of thermally stable, combustion-resistant polymer composites

Composites of the industrially important polymer, poly(methyl methacrylate)(PMMA), were prepared by free-radical polymerization of MMA with varyingamounts (1–30 wt. %) of sodium dioctylsulfosuccinate (Aerosol OT or AOT) surfactantadded to the reaction mixture. The composites with AOT incorporated show enhancedresistance to thermal degradation compared to pure PMMA homopolymer, andmicro-cone combustion calorimetry measurements also show that the composites arecombustion resistant. The physical properties of the polymers, particularly at low concentrations of surfactant, are not significantly modified by the incorporation of AOT,whereas the degradation is modified considerably for even the smallest concentrationof AOT (1 wt. %). Structural analyses over very different lengthscales were performed.X-ray scattering was used to determine nm-scale structure, and scanning electron microscopy was used to determine �m-scale structure. Two self-assembled species wereobserved: large phase-separated regions of AOT using electron microscopy and regionsof hexagonally packed rods of AOT using X-ray scattering. Therefore, the combustionresistance is observed whenever AOT self-assembles. These results demonstratea promising method of physically incorporating a small organic molecule to obtain ahighly thermally stable and combustion resistant material without significantly changingthe properties of the polymer.