In this work, the motional dynamics and relaxation behavior of a series of model poly(dimethylsiloxane)co-meta-carborane (PDMS-co-CB) hybrid elastomers have been studied in depth, using Broadband Dielectric Spectrometry over a temperature range of -130 to 100 degrees C and a frequency window of 10(-1) to 10(7) Hz. The segmental alpha-relaxation of both the PDMS and carborane chain segments has been characterized at specific carborane backbone incorporation levels. A direct correlation between the ratio of PDMS to carborane segments and the motional constraint of the network as a whole was observed. In addition to the study of the alpha-motional modes associated with local intra-segmental motions and the onset of cooperative motion, we have also identified and studied a higher order cooperative (normal-mode) motion of extended segments of the carborane-siloxane co-polymer chains at elevated temperatures. These normal mode motions have been shown to follow an Arrhenius temperature dependence, are sensitive to the local chemical environment and have not been previously reported in this class of polysiloxane copolymer. The motional dynamics of the PDMS-co-CB networks have been compared and contrasted with those of a series of conventionally filled PDMS-Boron Nitride (PDMS-BN) composite systems. While the effects of the chemically bound carborane segment on the PDMS chain dynamics, local order and global network properties have been shown to be directly correlated, significant and predictable, the effects of the BN filler on the PDMS matrix are significantly less so and the results suggest that the filler material may in fact be disrupting the network order, with a consequently negative impact on the properties of the composite. (C) 2014 Elsevier Ltd. All rights reserved.