Molecular composites have been made from three types of ionic PPTA's and various polar polymers (PVP, S-AN, PVC, PEO), in which a good dispersion of rod molecules is achieved via ionic (ion-dipole) interactions. Optical/thermal testing and morphological observations by electron microscopes have indicated good dispersionof the rigid-rod PPTA molecules. Molecular composites based on amorphous matrix polymers are all transparent and show no phase separation upon heating; therefore, they are melt-processable. The deformation mode of the matrix polymer is modified significantly with the addition of rod molecules: e.g., while crazing is the only deformation mechanism of PVP and S-AN (30% AN), the addition of ionic PPTA molecules into these amorphous polymers induces shear deformation. This is due to interactions between rod and coil molecules at the molecular (or microscopic) level, unlike the situation in conventional fiber composites, in which interactions between fiber and matrix polymer occur only at the interface during load transfer. The observed deformation modes suggest that fracture properties of these molecular composites should be enhanced. Mechanical tests made on three different composite systems do show enhanced ductility (toughness) in addition to increased stiffness/strength for the molecular composites, having either an amorphous or semicrystalline polymer matrix.Conventional fibers for advanced composites, such as carbon fiber and Kevlar fiber, are aggregates of fibrils and microfibrils, and therefore they contain many inherent defects that can initiate cracks and lead to premature failure of the composite. The idea of "molecular (level) composites" is based on the fact that an individual rigid-rod molecule, such as a poly(p-phenylene terephthalamide) (PPTA) molecule, has no defect; therefore, the theoretical strength due to covalent bonds in the Corresponding author 0097-6156/96/0632-0054$15.00/0

No abstract

No abstract

No abstract

No abstract