In multiscale models for polymeric fluids, the evolution of the polymer chain is usually modeled using an entropic force, computed from the free energy associated with the end-to-end vector. We will present results which aim at justifying under which circumstances such a dynamics is indeed close to the original dynamics based on the full-atom chain. References: F. Legoll and T. Lelièvre, Effective dynamics using conditional expectations, Nonlinearity, 23, 2131-2163, (2010). F. Legoll, T. Lelièvre and S. Olla, Pathwise estimates for an effective dynamics, Stochastic Processes and their Applications, 127, 2841-2863, (2017). F. Legoll, T. Lelièvre and U. Sharma, Effective dynamics for non-reversible stochastic differential equations: a quantitative study, Nonlinearity, 32(12), 4779, (2019)