AN AB-INITIO STUDY OF THE STRUCTURAL AND PHYSICAL-PROPERTIES OF A NOVEL RIGID-ROD POLYMER - PIPD

In this article, we present the first ab initio calculations on the no vel rigid-rod polymer PIPD using density functional techniques. The be haviour of the molecular chain under strain is studied and the chain m odulus agrees excellently with experiment. Two crystal structures are considered and hydrogen bonding networks as proposed from X-ray diffra ction measurements are demonstrated to exist. Negligible energy differ ences were found and both structures could exist at room temperature. The electronic structure reveals a pi - pi interaction Like in graphit e, resulting in a weak bonding. The interaction due to the hydrogen bo nding network is smaller, however: it leads to a significantly larger bonding energy. As the interchain bonding in PIPD is approximately 3 t imes the bonding without the network, the improvement in the compressi ve strength of PIPD compared to PBO and PET can be attributed to the h ydrogen bonding network. (C) 1998 Elsevier Science Ltd. All rights res erved.