COMPUTER MODELING OF (110) ADJACENT REENTRY OF POLYETHYLENE MOLECULES

Conformations of adjacent reentry folds of polyethylene have been exam ined using molecular mechanics techniques. In addition to the lowest e nergy conformation (g(-)g(-)g(+)g(+)tg(+)) described in previous studi es, other conformations with similar energies but different spatial ex tents were identified. In particular, a fold conformation was found wh ich was less than 1 kcal/mol higher in energy than the global minimum (g(+)g(+)tg(+)g(+)tg(+)). The effects of different fold conformations on fold surface packing and the lamellar structure of polyethylene cry stals were discussed. Fold energies for the five lowest conformations ranged from 4.5 to 6.2 kcal/mol. The small energy differences between the global minimum and the other conformations indicate that more than one fold type may be present in polyethylene crystals and should be c onsidered in fold packing simulations.