ABSTRACT Direct experimental access to the monomeric friction coefficient (ζ0) 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 Tg,B < T < Tg,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 ζ0 from the linear behavior in the rubber‐glass transition region, and to estimate the size of Gaussian submolecules. When compared at constant T – Tg, 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 ζ0 in filled systems. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 1437–1442 The motion of a polymer chain depends on the local friction (ζ0) experienced by its fundamental subunits (Gaussian submolecules). Knowledge of ζ0 is therefore a prerequisite to understand the viscoelastic response of the material in terms of its internal structure. In this article, a simple method is introduced to estimate ζ0 and the size of Gaussian submolecules in filled systems, such as filled rubbers or block copolymer thermoplastic elastomers at temperatures relevant for end‐use applications.