The dynamic mechanical measurements on several polymers filled with very fine silica particles revealed that these composites exhibit two tan delta peaks. One was related to the usual polymer glass transition, while the other, occurring at a higher temperature, was assigned to the glass transition of regions containing chains of reduced mobility. Since many aspects of this behavior were found to be analogous to those of random ionomers, the results support the validity of the EHM model of ionomer morphology. The particle content, the number of monomer units interacting strongly with the surface of the particles, the thermal history of the sample, and the average MW of the polymer were all found to have a significant effect on the area and the maximum of the new tan delta peak. These effects are discussed in terms of a model which is based on the EHM ionomer model but takes into account the formation of tightly bound and loosely bond polymer chains around the filler particles.