1. Preparation

1.1 Polyimide synthesis

Linear polyimides are synthesized by polycondensation of a dianhydride and a diamine in a two-step process, illustrated in figure 1 (preparation of the polyimide PMDA-ODA, analogous to DuPont's Kapton). The high reactivity of amines towards anhydrides enables an amic polyacid to be obtained in the first step by opening the anhydride ring. Heating in the presence of a catalyst enables cyclization with elimination of water, and the polyimide is obtained. In addition to cyclization, heating to around 300°C removes the polycondensation water and solvent.