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 varying amounts (1–30 wt. %) of sodium dioctylsulfosuccinate (Aerosol OT or AOT) surfactant added to the reaction mixture. The composites with AOT incorporated show enhanced resistance to thermal degradation compared to pure PMMA homopolymer, and micro-cone combustion calorimetry measurements also show that the composites are combustion-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 concentration of 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 μm-scale structure. Two self-assembled species were observed: large phase-separated regions of AOT using electron microscopy and regions of hexagonally packed rods of AOT using X-ray scattering. Therefore, the combustion resistance is observed whenever AOT self-assembles. These results demonstrate a promising method of physically incorporating a small organic molecule to obtain a highly thermally stable and combustion-resistant material without significantly changing the properties of the polymer

Thermal degradation of polystyrene, poly 1,4 butadiene and copolymers of styrene and 1,4 butadiene irradiated under air or argon with 60Co .gamma. rays

60Co-γ-irradiated samples of polystyrene (PSt), poly(1,4-butadiene), (PBD), and two poly(styrene-co-butadiene)s containing 25 and 75% BD were subjected to thermogravimetric analysis (TGA), in the presence and absence of O2. In the case of PSt the irradiation caused a significant shift in Tonset, the onset temperature for mass loss, to higher temperatures, whereas in the cases of the BD-containing polymers irradiation caused a decrease in Tonset (oxic irradiation) or had little or no effect on Tonset (anoxic irradiation). The amount of non-volatile residue formed in the cases of BD-containing polymers was augmented by γ-irradiation. The improved thermal stability of PSt is attributed to radiation-generated unsaturations acting as depolymerization retardants and/or agents in thermal crosslinking. Radiation-induced crosslinks do not affect the thermal behavior of PSt. In the cases of BD-containing polymers the thermal behavior is predominated by reactions of the carbon–carbon double bonds (crosslinking and cyclization). Radiation-induced chemical alterations, therefore, play a minor role during the thermal decomposition