Radical polymerization is widely applied in industrial production using peroxides as initiators. The high-pressure polymerization process of LDPE is evaluated of pressures up to 3500 bar and temperature up to 300 degrees C. For simulations physical properties and kinetics under these harsh conditions have to be measured. Therefore, kinetic parameters such as activation energy, pre-exponential factor and order of reaction as well as their dependence on pressure and solvent are investigated in this study with high-pressure calorimetry using a transitiometer and DSC using high-pressure crucibles.