Polymer Chemistry

The most common way to synthetize polyimides involves the polycondensation of diamine and dianhydride monomers in solution. The reaction is in general achieved in two steps; first, an intermediate poly(amic acid) is formed, which is further cyclized into polyimide upon appropriate heating. In this solution polymerization process, high boiling temperature solvents are mainly used, such as N-methyl-2-pyrolidone. As such solvents are hazardous chemicals, there is a real interest to develop an approach preventing their use. To this end, some research works have been recently reported concerning the imidization into an extruder of a poly(amic acid) solution in dichlorobenzene. The drawbacks of this process remain in the solvent elimination and the total reaction time (several hours). In the frame of our project, we developed a method for obtaining polyimides directly in solvent-free conditions via a reactive extrusion process, within typical extrusion residence times (5– 10 minutes). Trial runs have been performed on 15 mL microcompounder. The optimization of the shear conditions and of the reaction temperature allowed obtaining polyimides within a reaction time ranging from 3–5 minutes. The scaling up of this process has been carried out using a twin screw extruder (L/D = 60). The polyimides obtained were characterized by both 1H and 13C NMR. The molar masses of the polyimides were obtained by size-exclusion chromatography. FT-IR spectroscopy has been used to confirm the imide structure and the imidization conversion rate has been determined by DSC.