Approximate methods of the calculation of effective energies in disordered chains I. Comparative theoretical study of the energy properties of structural isomers of polypropene

The synthesis of conformational isomers of long oligomers built up from propene units can be controlled. Propene may polymerize to long isotactic, syndiotactic or atactic chains depending on the experimental conditions, especially the catalyst. The total energies of these conformational isomers, having the methyl groups either all on one side, or alternating sides or randomly distributed are different as a result of the different interactions. We have calculated the total energies and effective energies per propene unit of polypropene in different conformations with the help of the elongation method and the direct cluster approach, respectively. These results are compared with each other and in addition with ab initio Hartree-Fock crystal orbital calculations on infinite periodic polypropene chains. (C) 1999 Elsevier Science B.V. All rights reserved.