| Ionic rigid polymers and their molecular composites based on two types of ionic rigid-rod polymers, poly((p-phenylene terephthalamido)propane-sulfonate) (PPTA-PS), and poly(N,{dollar}rm Nspprime{dollar}-(sulfo-p-phenylene) terephthalamide) (S-PPTA) with various counterions have been prepared. In ionic PPTAs, several characterization tools, such as thermogravimetric analyzer (TGA), infrared spectroscopy (IR), molecular dynamics modeling and scanning electron microscopy (SEM), are conducted to study the structure-property relationship. Non-directional ionic bonding can provide us a good route to enhance solubility in organic solvents while maintaining properties of the polymers in the solid state. Thermal stability of ionic PPTA relies on structure as well as counterion type. In addition, ion-modification of PPTA also can be processed to a solid-state form, which goes beyond the conventional methodologies and fully exploit their unique advantages as structural polymers since developed in 1970s.; In the molecular composites, the good dispersion of ionic rigid polymers in flexible amorphous polymer matrix has been achieved via ionic interactions. A single Tg in DSC and DMTA, optical clarity and TEM observation, indicate that the ion-dipole interactions provide a good route to overcome the tendency of rigid polymers to aggregate in matrix polymers. Small-angle X-ray scattering (SAXS) study, by using the Guinier's law and D-B model, suggests that the miscibility of the molecular composites reaches to a segmental level. Deformation and fracture behavior of the molecular composite made of ionic PPTA and an amorphous matrix polymer, poly(4-vinylpyridine) (PVP) or poly(styrene-co-acrylonitrile) (30%AN), has also been investigated: both strength/stiffness and toughness are improved when deformation mode changes from crazing to shear deformation.; Upon replacement of a monovalent counterion to a divalent one, the composites develop more extended rubbery plateau in DMTA data and shear deformation zones under simple tension, observed by TEM. It is suggested that divalent counterions are more effective in improving the fracture properties of the molecular composites. |
