Conversion of renewable vanillin into high performance polyimides via an asymmetric aromatic diamine derivation

Abstract

In this paper, a new asymmetric bio-based diamine MAAMB containing phenoxyl-benzyloxyl linkage and a pendent methoxyl group, was synthesized starting from the aromatic, lignin-derivative vanillin through three steps. Two series of polyimide (PI) films were prepared by condensing MAAMB or an analogous, symmetric diamine 1, 4, 4′-APB with four different dianhydride 6FDA, ODPA, BTDA, or BPDA, respectively, via classic two-step procedure. Comparative studies between the MAAMB-resulting PI series (APIs) and 1, 4, 4′-APB-resulting PI series (SPIs) reveal that the introduction of benzyl linkage and pendent methoxyl group in MAAMB imparts APIs with better solubility in organic solvents, higher optical transparence with 63.7–89.2% at 500 nm. Meanwhile, API series retain good thermal properties with Tg ranging in 241–262 °C, T5 ranging in 448–478 °C, and favorable mechanical properties with tensile strengths ranging in 82.2–92.7 MPa and tensile modulus ranging in 2.27–2.53 GPa. Additionally, APIs exhibit lower water absorption (0.71–1.01%) and surface energy (31.35–42.03 mN/m) than those (0.75–1.25%) and (34.06–44.35 mN/m) of the analogous SPIs. It indicates that the renewable vanillin could be employed to prepare bio-based polyimides with balanced comprehensive properties. This work presents a potential pathway of converting the renewable aromatic vanillin into high performance PI materials.