The molecular composites of a rigid polymer polyindde (PI) with a flexible matrix polymer polyvinylpyrrolidone (PVP) were successfully synthesized by in-situ polycondensation. A strong specific interaction of acid-base between the polyamic acid (the precursor of PI) and the PVP was confirmed experimentally. By this specific interaction the ndscibility of PI with PVP was substantially improved.The PI dispersed in the PVP matrix polymer on a molecular level or nearly molecular level.The films of the molecular composites of PI/PVP are transparent.Only one Tgexhibited over the whole composition range suggesting a homogeneous phase.No phase separation was observed by SEM for the sample with PI content 40% the finely dispersed rod-like PI micro-crystals can be found by SEM. Due to the molecular composite formation of PVP with PI

the PVP become insoluble in ethanol even with only 10% PI.