Structure and properties of poly(methyl methacrylate) (PMMA)-fullerene (C$_{60}$) nanocomposites

We examined the rheological and dynamical mechanical (DMA) properties of PMMA-C$_{60}$ nanocomposite materials with relatively low concentrations of C$_{60}$, 0.1-5wt{\%}. Decreases of the glass transition temperature (T$_{g})$, $\sim $7 $^{o}$C, were observed in samples with 0.5 and 1 wt{\%} C$_{60}$. The decreases in T$_{g}$ are connected to decreases of the longest relaxation time measured for the system. The plateau modulus of the composites was enhanced relative to the homopolymer but did not increase monotonically with C$_{60}$ concentration. The relative changes of the relaxation time, the plateau modulus and T$_{g}$ cannot be explained by the Doi-Edwards model and appear to be connected to the distribution of the nanoparticles, as determined by electron microscopy.