CHAIN-FOLDING CONFORMATIONS IN ISOTACTIC POLYPROPYLENE

Chain-folding structures of alpha-form isotactic polypropylene were in vestigated. Conformations of adjacent re-entry folds in the (100) and (140) planes were examined using molecular dynamics and molecular mech anics techniques. Folding energies, calculated by varying the number o f chain fragments of folding molecules, took a minimum value every thr ee monomers. Inversions between left- and right-hand helices at foldin g positions were expressed by torsion angles of the main chain without configurational change. As a result, chain folding manner could be di splayed through conformational change of the main chain, keeping the o rder of helical conformations in crystal lattice, that is, left- or ri ght-hand helices and up or down direction of the methyl group to the m ain chain.