Proposed is semiempirical equation-of-state model for organic compounds over a broad region of thermodynamic parameters, which takes into account transformations of substances at high dynamic pressure. Equations of state for polystyrene, polyimide, and poly(m-phenilene isophthalamide) are developed; the critical analysis of calculated results in comparison with the set of available at high energy density experimental data is made. ©2000 American Institute of Physics.