  Adding plasticizers is a well-known procedure to reduce the glass transition
temperature in polymers. It has been recently shown that this effect shows a
non-monotonic dependence on the size of additive molecules [The Journal of
Chemical Physics 150 (2019) 024903]. In this work, we demonstrate that, as the
size of the additive molecules is changed at fixed concentration, multiple
extrema emerge in the dependence of the system's relaxation time on the size
ratio. The effect occurs on all relevant length scales including single monomer
dynamics, decay of Rouse modes and relaxation of the chain's end-to-end vector.
A qualitatively similar trend is found within mode-coupling theoretical results
for a binary hard-sphere (HS) mixture. An interpretation of the effect in terms
of local packing efficiency and coupling between the dynamics of minority and
majority species is provided.
