Monodisperse micron-sized poly (styrene/hexanedioldimethacrylate) particles of interpenetrated polymer network (IPN) were produced by the seeded polymerization in the presence of polystyrene seed particles. In order to evaluate the crosslinking density of the final particle, a thermodynamic equation was proposed considering the effective swelling of the solvent. Based this values, the elasticity of the particles was predicted, which were compared with the ones obtained from the compressive mechanical test. In the light of thermodynamics, it was elucidated that an effective crosslinking could be achieved with changing the amount of crosslinking agent without further phase separation. After the polymerization, the poly (styrene/hexandiol) particles were obtained around 10 μm, consequently displaying a good elasticity.