In this paper we consider time dependent Schr"odinger linear PDEs of the form Im $\partial_t \psi = L(t)\psi$, where $L(t)$ is a continuous family of self-adjoint operators. We give conditions for well-posedness and polynomial growth for the evolution in abstract Sobolev spaces. If $L(t) = H +V(t)$ where $V(t)$ is a perturbation smooth in time and $H$ is a self-adjoint positive operator whose spectrum can be enclosed in spectral clusters whose distance is increasing, we prove that the Sobolev norms of the solution grow at most as $t^\epsilon$ when $t\mapsto \infty$, for any $\epsilon >0$. If $V(t)$ is analytic in time we improve the bound to $(\log t)^\gamma$, for some $\gamma >0$. The proof follows the strategy, due to Howland, Joye and Nenciu, of the adiabatic approximation of the flow. We recover most of known results and obtain new estimates for several models including $1$-degree of freedom Schrödinger operators on $\mathbb{R}$ and Schrödinger operators on Zoll manifolds. This is a joint work with Didier Robert.