Solvent-Free Reactive Extrusion As an Innovative and Efficient Process for the Synthesis of Polyimides

Polyimides are commonly synthesized in a 2-step solution polymerization process. Such process requires long reaction times as well as specific care due to the use of potentially harmful solvents. In the present study, the total reaction time for producing polyimides has been lowered to less than 10 min by using a solvent-free continuous reactive extrusion process. The proof of concept was determined with the system based on 3,3',4,4'-benzophenone-tetracarboxylic dianhydride (BTDA) and an aliphatic diamine, Jeffamine D-230 within a microextruder. Degrees of conversion to polyimide, determined with C-13 NMR and DSC analysis, are over 90 mol % after 5 min of extrusion at 180 degrees C, 200 degrees C, and 225 degrees C, respectively. These syntheses were then transferred to a twin-screw extruder to form linear aliphatic-aromatic polyimides with two types of dianhydride: BTDA and pyromellitic dianhydride (PMDA). Comparison with a conventional solution polymerization process showed no significant differences in the polymers characteristics. The polyimides produced with this method presented glass transition temperatures ranging from 5 to 90 degrees C. The number-average molar masses measured were between 11 000 and 15 000 g.mol(-1).