**2.8 PIs derived from fatty diamines**

Many of the PIs' characteristics are an outcome of the hard blocks coming from both the dianhydride and diamine segment. By replacing one of them with a softer block of natural origin, bio-based PIs with interesting traits are obtained. For example, a long, branched, cycloaliphatic, fatty diamine was employed as the soft block together with several, flexible or rigid, hard aromatic dianhydrides in the construction of some PIs, and the effect of the soft-hard combination was investigated [66].

The integration of flexible (or bulky) hard segments containing various spacers provided amorphous PIs, while the use of a highly rigid dianhydride segment yielded a semicrystalline polymer with separated nanophases after annealing.

The soft-hard combination resulted in highly soluble, processable, thermoplastic PIs of moderate molecular mass, with Tg values near room temperature, yet relatively thermal stability. They display superior processability as compared to most polyimides and are also available for recycling without significant changes in their outstanding mechanical features.

The four materials displayed high elongations (especially the one containing the highly rigid hard segment) and qualify as trustworthy candidates for applications that require high damping characteristics in ambient conditions (shock absorbers, noise, or vibration insulating materials, sealants).

Further studies revealed a self-healing capacity of these materials at room temperature. Rheological and tensile investigations proved the two-step kinetics and physical characteristic of the healing process and its dependency on the particular relaxation behavior of the PIs during stepwise healing. Mechanical integrity is maintained during healing due to the interplay of primary and secondary interactions between the soft and hard structural motifs [67, 68].

Another fatty diamine, the commercial Priamine™ 1074 coming from vegetable extracts (tall oil and soybean oil), was used as a starting material in the synthesis of partially bio-based fluorinated PIs.

The dimer containing fully renewable C36 enabled the preparation of highly soluble, thermally resistant PIs with a high content of biomass (up to 48.9%). During the two-stage polycondensation process, additional building blocks were used to ensure double-bond terminal groups which were further employed in the preparation of UV-cross-linked coatings. The obtained materials can satisfy some key requirements of microelectronics photoresists, like high optical transparency, adequate thermal stability, low water absorption, and suitable adhesion [69].
