  We study the long-time behaviour of a nonlinear Fokker-Planck equation, which
models the evolution of rigid polymers in a given flow, after a closure
approximation. The aim of this work is twofold: first, we propose a microscopic
derivation of the classical Doi closure, at the level of the kinetic equation ;
second, we prove the convergence of the solution to the Fokker-Planck equation
to periodic solutions in the long-time limit.
