Atomic detail simulation studies of unsubstituted and substituted poly(p-phenylene terephthalate)s

Results of computer simulations of poly(p-phenylene terephthalate) (PPT) an d 1.4-phenylene-2-octyloxy terephthalate (PTA8) are presented. The structur es obtained from the NPT dynamics simulations were studied and compared at an atomistic level, at four different temperatures: 300, 450, 575 and 625 K . The side chains of PTA8 force the aromatic units into a planar orientatio n instead of the staggered structure of PPT. The planar orientation causes the decreasing of the strong non-bonded interactions between the neighbouri ng main chains. Additionally, it enables the regular staggered arrangement of the main chains in a stack of chains in order to get better packing. The staggered structure of the aromatic units remains at all temperatures for PPT. In the case of PTA8, the orientation gets more or less random as a fun ction of temperature. Both polymers, PPT and PTA8, are relatively extended, but the end-to-end distances of PTA8 decrease similar to 4 Angstrom as the temperature is raised from 300 to 625 K. The dihedral distribution of the side chains gets random as the temperature increases. (C) 2000 Elsevier Sci ence Ltd. All rights reserved.