Preparation, characterization, and bio-degradation studies of high-performance bio-based polyimides based on bicyclic diamines derived from citric acid

Abstract

Two new bioderived diamines with two cis-fused cyclopentane ring structures, bis(4-aminophenyl) (octahydropentalene-2,5-diyl)dicarbamate (OAC) and 4,4′-((octahydropentalene-2,5-diyl)bis(oxy))dianiline (OOD), were designed and synthesized from natural citric acid for the first time. Two series of new bio-based polyimides ((PI(B/F/HAC) and PI(B/F/HOD)) were developed by the polymerization of OAC and OOD with three commercial dianhydrides, respectively. Due to the introduction of the two cis-fused cyclopentane ring structures with optically asymmetric active carbon atoms, the as-prepared polyimides exhibit light color or even colorless and transparent properties, as well as interesting optical activities. The transmittance at 400 nm and total optical transmittance (380–800 nm) for PI(HAC) are 83.5% and 86.6%, and those for PI(HOD) are 84.3% and 88.5%, respectively. PI(BAC) containing carbamate moieties in the polymer backbone shows excellent dimensional stability and mechanical properties, with a coefficient of thermal expansion (CTE) value below 18 ppm k⁻¹ (close to that of Cu), a tensile strength of 115.8 MPa and a modulus of 2.9 GPa. The relationship between the structure and properties of polymers was also investigated through molecular simulation and Gaussian calculations. In addition, we have studied the biodegradable behaviors of these bio-based polyimides. After 49 days of degradation by porcine pancreatic lipase, the number average molecular weight and weight average molecular weight of PI(FAC) changed by approximately 75% and 90%, respectively, which proved to be a potential solution to the environmental problems caused by polyimide. This work provides new ideas for the development of new biomass functional monomers, chiral polymers, and biodegradable polyimides, which have strong academic exploration value.