  We perform the calculation for tree-level ultraviolet unitarity violation
scales for scalar-$R^2$ inflation models by including an additional $R^2
|\Phi|^2$-type term. Due to certain constraints, we resort to the Einstein
frame for our calculations, where we separate our analysis between metric and
Palatini formulations. We follow recent works in this line that debunk the
naive predictions for unitarity violations in Higgs' inflation models to
determine how to accurately estimate the behaviour of scattering amplitudes in
the UV limit. Later, we work out different cases by assuming potentials
corresponding to known inflation scenarios so we could predict the range of
coupling parameters for which the theories would remain unitary up to the
Planckian regime. We also try to find the behaviour of the scattering
amplitudes for these theories during the transition from inflationary to
reheating epoch.
