Semicrystalline polyetherketoneketone (PEKK) is widely used as the matrix in carbon-fiber composites. Understanding and predicting the crystallization thermodynamics and kinetics of this class of polymers is, thus, of great interest. This paper uses molecular dynamic (MD) simulations using Dreiding united-atom (UA) potentials to characterize a wide range of thermos-physical properties of PEKK. We characterized the effect of terephthaloyl chloride to isophthaloyl chloride (T/I) on an extensive set of properties, including the lattice parameters and stability of PEKK crystal structures, glass transition temperature, melting temperature, crystal/amorphous interfacial energy, and enthalpy of fusion. We find good overall agreement between predicted properties and experimental values and the simulations help clarify inconsistencies in the literature. In combination with classical nucleation theory, nucleation barriers and critical nucleus size at different temperature are predicted.