The Heat and Free Energy of Polymerization of Ethylene

Abstract

Values calculated from available thermochemical and chemical thermodynamic data are given for the heats and free energies of polymerization of gaseous ethylene to gaseous, straight‐chain polyethylene (monoolefin) molecules of various lengths. Equations are given expressing these properties at 25°C as functions of n, the number of ethylene units per polymer molecule, for n≧3. The limiting values at 25°C for long‐chain molecules are ΔH_p°=−22.348 kcal. per ethylene unit, ΔF_p°=−12.186 kcal. per ethylene unit. A preliminary value for the heat of combustion of solid polyethylene at 25°C, ΔH_c°=−311.8 kcal. per ethylene unit, is combined with other data to obtain the value ΔH_p°=−25.4 kcal. per ethylene unit for the heat of polymerization of gaseous ethylene to solid polyethylene. This experimental value and the calculated value for gaseous polyethylene are shown to be consistent within reasonable limits when account is taken of the heat of sublimation of the partly crystalline polyethylene, estimated to be 3.6 kcal. per ethylene unit. Values are given graphically and in tabular form for the equilibrium concentrations of ethylene and all its polymers at various temperatures in a mixture in the ideal gas state at a pressure of 1 atmosphere.