Chemical and Biomolecular Research Papers -- Faculty Authors Series


Date of this Version

November 1992


Published by American Physical Society. Phys. Rev. B VOLUME 46, NUMBER 18, 1 NOVEMBER 1992. Copyright © 1992 American Physical Society. Used by permission.


Semicrystalline structures involving molecular packing and optimized chain conformations of three polyimides have been obtained with the CHARMM moleculardynamics program, and their densities calculated. An eclipsed conformation of face-toface stacking of polymer chains with a relative shift is observed, and the shift is found to depend upon the molecular characteristics of the planar unit and chain linearity. Threedimensional structures obtained by calculating the optimized edge-on confirmation of the stacked units yield the smallest calculated density for PMDA-ODA, namely 1.515 g/cm3, followed by BPDA-PDA with 1.644 g/cm3 and PMDA-PDA with 1.712 g/cm3. Both PMDA-ODA and BPDA-PDA reveal planar zigzag structure, and the former shows the largest undulation measured by the maximum difference in surface elevation on the surface cleaved along the edge-on bonds. PMDA-PDA reveals flat planar structure.