**3. Green and nonconventional synthesis and processing of polyimides**

As mentioned earlier, PIs are not usually produced by eco-friendly synthetic methods, especially in terms of solvents and thermal conditions. As detailed in the previous section, the production of some bioPIs starting from renewable building blocks involves the use of heavy-duty, rather toxic solvents (cresols in particular), with a negative environmental impact. This is a drawback which needs further research dedicated to greener experimental conditions.

On the other side, a large number of research studies were dedicated in the last two decades to the progress of nonconventional synthetic platforms or experimental conditions which can be used with some undeniable success in the development of PI-based materials. These come quite close to the strict criteria of green or sustainable chemistry based on ecological synthesis.

In this section, we will focus on some less harmful experimental conditions like synthesis (and processing) in ionic liquids, supercritical fluids, microwave conditions, and other nonconventional methods, as depicted by the scientific literature of the last 10 years.
