The effect of addition of fillers (carbon black (CB), carbon silica dual phase filler (CSDPF), and nanoclays) on the relaxation behavior of chlorobutyl vulcanizates has been Studied. The primary relaxation (a-transition, the glass transition) was Studied by dynamic mechanical analysis as a function of temperature (-60 to +100 degrees C) and positron annihilation life time spectroscopy (-70 to +110 degrees C). Irrespective of the filler and its loading, all the composites showed the glass transition temperature in the range of -29 to -33 degrees C, which was explained on the basis of relaxation chain dynamics of polyisobutylene in the vicinity of fillers. The secondary relaxation (alpha* or beta relaxation) was studied using dielectric relaxation spectra in the frequency range of 100-10(6) Hz. Nanoclays had a profound influence on the secondary relaxation, whereas CSDPF and CB had a marginal effect. The nonlinear strain dependent dynamical pararneters were also evaluated at double strain amplitudes of 0.07-5%. The nonlinearity in tan 8 and storage modulus has been explained on the concept of filler-polymer interactions and the interaggregate attraction (filler networking). The "percolation limit" of the fillers in the composites has been studied by DC conductivity measurements. (c) 2006 Wiley Periodicals, Inc.