Graphite oxide (GO) was modified using 3-aminopropyltriethoxysilane (APTES) to investigate the impact of dispersion and interfacial bonding on the mechanical properties of reinforced silicone elastomer, poly (dimethylsiloxane), PDMS. Although a 71% enhancement of Young's modulus was observed (comparable to thermoplastics) at a loading of 3.0 wt% APTES-modified GO (A-GO), the observed enhancement factor is just 8% of that expected for randomly dispersed perfect graphene sheets. We attribute this less-than-ideal enhancement to crumping and break-up of the graphene sheets caused by ultrasonic dispersion. In the absence of TEOS crosslinker, the A-GO PDMS melt does not solidify so modulus enhancement is not due to crosslinking through the APTES-modified filler particles. Modulus enhancement due to rubber-like elasticity of the filler itself, however, may be active. Characterization indicates that amino groups are chemically attached to the surface of GO in A-GO. The improved dispersibility enhances the toughness, but only at low loadings. In fact, at 3-wt% loading the toughness is less than that of pure PDMS due to loss of elongation caused by filler aggregation. (C) 2013 Elsevier Ltd. All rights reserved.