Chain-Folding Conformations in Isotactic Polypropylene

Chain-folding structures of α-form isotactic polypropylene were investigated. Conformations of adjacent re-entry folds in the (100) and (140) planes were examined using molecular dynamics and molecular mechanics techniques. Folding energies, calculated by varying the number of chain fragments of folding molecules, took a minimum value every three monomers. Inversions between left- and right-hand helices at folding positions were expressed by torsion angles of the main chain without configurational change. As a result, chain folding manner could be displayed through conformational change of the main chain, keeping the order of helical conformations in crystal lattice, that is, left- or right-hand helices and up or down direction of the methyl group to the main chain.