Molecular Design of Soluble Biopolyimide with High Rigidity.

New soluble biopolyimides were prepared from a diamine derived from an exotic amino acid (4-aminocinnamic acid) with several kinds of tetracarboxylic dianhydride. The biopolyimide molecular structural flexibility was tailored by modifying the tetracarboxylic dianhydride moiety. The obtained polyimides were soluble in various solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, N,N-dimethylformamide, dimethyl sulfoxide, and even tetrahydrofuran. It was observed that the biopolyimide solubility was greatly dependent upon the structural flexibility (torsion energy). Flexible structure facilitated greater solubility. The synthesized biopolyimides were largely amorphous and had number-average molecular weight (Mn) in the range (5⁻8) × 10⁵. The glass transition temperatures (Tg) of the polymers ranged from 259⁻294 °C. These polymers exhibited good thermal stability without significant weight loss up to 410 °C. The temperatures at 10% weight loss (Td10) for synthesized biopolyimide ranged from 375⁻397 °C.