Computer simulations of condensed phases and biochemical systems have lead to profound new insight into molecular-scale phenomena occurring in these complex systems. Many processes that occur in liquids, soft materials, and biochemical systems however occur over length and time scales that are well beyond the current capabilities of atomic-level simulations. In the field of polymers, there are many simulation techniques and models that span a range from the atomistic scale to the continuum. In recent years, much research has been focused on linking models of different length scales, especially from detailed, fully atomistic to mesoscopic scales and back. A common way of addressing this issue is to develop coarse-grained (CG) models from full-atomistic simulations by merging groups of chemically connected atoms into superatoms. This PhD thesis describes new developments in the field of CG simulations of polymers. In addition to CG simulations, atomistic molecular dynamics calculations are performed as well to study properties of polymers.