Elastomers built up through the π-π Stacking association of polycyclic planar aromatic diimides

Polymers composed of polycyclic aromatic planar diimide (PCAD) units and flexible rubbery poly(propylene glycol) (PPG) chains were synthesized, and the morphology and viscoelasticity were investigated. The polymers were synthesized by polycondensation of naphthalene or perylene tetracarboxylic dianhydrides with PPG-diamines and subsequent thermal imidization. The thermal and viscoelastic properties were measured by differential scanning calorimetry and dynamic mechanical analysis, respectively. The molecular aggregation structure was explored by infrared spectroscopy, wide-angle X-ray diffraction and small-angle X-ray scattering measurements. The PCAD units associate in the PPG continuum by the electromagnetic interaction of π electrons on the planar aromatic rings to build a stacked structure. The morphology and viscoelastic characteristics depend on the PCAD structure and molecular weight of the PPG segments, and the polymers composed of perylene diimide units and high molecular weight PPG chains show rubber elasticity because of the well-segregated morphology. The thermal stability was enhanced by PPG chain end capping by thermally stable PCAD units.