The role of intermolecular interactions in determining the mode of packing of crystalline polymers. Energy calculations on isotactic polypropylene

Packing energy calculations for isotactic polypropylene chains have been performed with the purpose: (a) to predict the most stable kind of monoclinic lattice for the α-modification; (b) to contribute to the understanding of the structural disorder which is commonly found in the α-modification; (c) to evaluate the order of magnitude of the differences in energies among the three modifications (α, β, γ) experimentally observed. The results for the α-form show that the best packing of the chains is achievable for the ordered P2₁/c space group, while more or less disordered structures may exist, which only slightly differ in energy from the most stable structure. In connection with point (c), our results are in agreement with the possibility of polymorphism in isotactic polypropylene.