Direct experimental access to the monomeric friction coefficient (zeta(0) ) relies on the availability of a suitable polymer dynamics model. Thus far, no method has been suggested that is applicable to filled systems, such as filled rubbers or microphase-segregated A-B-A thermoplastic elastomers (TPEs) at T-g,T-B < T < T-g, A. Building upon the procedure proposed by Ferry for entangled and unfilled polymer melts, the Rouse-Bueche theory is applied to an undiluted triblock copolymer to extract zeta(0) from the linear behavior in the rubber-glass transition region, and to estimate the size of Gaussian submolecules. When compared at constant T - T-g, the matrix monomeric friction factor is consistent with the corresponding value for the homopolymer melt. In addition, the characteristic Rouse dimensions are in good agreement with independent estimates based on the Kratky-Porod worm-like chain model. These results seem to validate the proposed approach for estimating zeta(0) in filled systems. (C) 2016 Wiley Periodicals, Inc.