AB INITIO CALCULATIONS OF THE DEFORMATION OF POLYETHYLENE.

Ab initio H-F SCF quantum-mechanical calculations of the energy of covalent bond deformation of a - CH//2CH//2 - ethylene repeat unit at strains up to epsilon equals 0. 6 are reported. The computational scheme involves subtracting energies of axially strained normal paraffins (n-C//3H//8, n-C//5H//1//2, and n-C//7H//1//6) differing in length by one ethylene unit. At small strains it is shown that the deformation is contributed to equally by C-C bond stretch and by CCC bond angle opening. At higher strains the majority of the deformation is accomplished by C-C stretch. The calculated elastic modulus is 405 GPa and the tensile strength of the polymer in the chain direction is 66 GPa.