High density poly(ethylene) (HOPE) is functionalized with two different esters namely, amino ester and hydroxyl ester in an inert atmosphere at 160 degrees C under different experimental conditions by thermolysis method. The order of functionalization and olefin formation reactions are determined through FTIR spectroscopy. The energy of activation of different chemical reactions also determined from FTIR-RI method. Thermo gravimetric analysis and differential scanning calorimetric methods are used to access the thermal properties of the functionalized HDPE. Plausible reaction mechanism is proposed here to explain the experimental results obtained. (C) 2010 Elsevier B.V. All rights reserved.