A multi-scale model that can simulate the influence of the synthetic conditions (e.g., molar ratio) on the structure and physical properties of thermosetting resins (e.g., phenol resin) through the introduction of a comprehensive reaction model that includes the addition reaction was developed and reported herein. The effectiveness of the model was validated by verifying the influence of the primary synthetic index, i.e., the molar ratio, on the physical and thermal properties (i.e., density and glass transition temperature) of Resol resins. This model can aid in developing more efficient and suitable synthetic conditions to obtain products exhibiting the desired material properties.