Highly Soluble Fluorinated Polyimides Synthesized with Hydrothermal Process towards Sustainable Green Technology

Polyimides, a widely used engineering plastic, require use of large amounts of toxic and hazardous organic solvents which threaten our daily lives, calling for new and easy synthetic methods for sustainable environmentally friendly development. In this paper, highly soluble fluorinated polyimides based on 4,4′-(hexafluoroisopropylidene) diphthalic anhydride were synthesized via hydrothermal process without using any toxic organic solvents and the advantages of the newly demonstrated synthetic methods are shown by comparative analysis performed with the two conventional synthetic methods using organic solvent: thermal and chemical imidization. Lower temperature is required (~200 °C) compared to thermal imidization and functional groups for high fusibility formed more easily compared to chemical imidization. According to the comparative analysis, hydrothermally synthesized PIs showed excellent solubility and maintained high thermal stability (>500 °C) and glass transition temperature (>300 °C) compared to conventional PI. The hydrothermally synthesized polyimide is much more convenient to store and manage than other form of polyimide which is much more stable when it is exposed to humidity as it is a powder form. The hydrothermal synthetic method is verified to be a “Green” and facile method for sustainable PI synthesis.

Colorless Polyimides Derived from an Alicyclic Tetracarboxylic Dianhydride, CpODA

An alicyclic tetracarboxylic dianhydride having cyclopentanone bis-spironorbornane structure (CpODA) was polycondensated with aromatic dianhydrides to form the corresponding poly(amic acid)s which possessed logarithmic viscosities in the range 1.47–0.54 dL/g. The poly(amic acid) was imidized by three methods: a chemical, a thermal, and a combined chemical and thermal process. In a thermal method, imidization temperature markedly influenced the film quality and molecular weight of the polyimide. When the poly(amic acid) was cured over the Tg of the corresponding polyimide, the flexible polyimide films were obtained and the molecular weights increased several times, which means that the post-polymerization took place. In spite of low-temperature cure below Tg flexible films with the imidization ratio of 100% were fabricated by a combined chemical and thermal imidization technique. The films possessed the decomposition temperatures in a range of 475–501 °C and Tgs over 330 °C. The high Tg results from a dipole–dipole interaction between the keto groups of the polymer chains as well as development of the rigid polyalicyclic unit. The polyimide films exhibited CTE between 17 and 57 ppm/K. All the films fabricated were entirely colorless and possessed the λcut-offs shorter than 337 nm. Notably, the films prepared by a chemical method exhibited outstanding optical properties.

Polyimide-Derived Carbon-Coated Li4Ti5O12 as High-Rate Anode Materials for Lithium Ion Batteries

Carbon-coated Li4Ti5O12 (LTO) has been prepared using polyimide (PI) as a carbon source via the thermal imidization of polyamic acid (PAA) followed by a carbonization process. In this study, the PI with different structures based on pyromellitic dianhydride (PMDA), 4,4′-oxydianiline (ODA), and p-phenylenediamine (p-PDA) moieties have been synthesized. The effect of the PI structure on the electrochemical performance of the carbon-coated LTO has been investigated. The results indicate that the molecular arrangement of PI can be improved when the rigid p-PDA units are introduced into the PI backbone. The carbons derived from the p-PDA-based PI show a more regular graphite structure with fewer defects and higher conductivity. As a result, the carbon-coated LTO exhibits a better rate performance with a discharge capacity of 137.5 mAh/g at 20 C, which is almost 1.5 times larger than that of bare LTO (94.4 mAh/g).

Photoluminescence, thermal and surface properties of triarylimidazole-containing polyimide nanocomposite films

Three series of triarylimidazole-containing polyimide nanocomposite films were prepared via thermal imidization. Due to the introduction of inorganic nanoparticles including SiO2, Al2O3 and Si3N4, the fluorescence intensities of these composite films were clearly increased.

Hydrophobic and hydrophilic modification of hierarchically porous monolithic polyimide derivatives as functional liquid absorbers

Thermally induced phase separation (TIPS) and thermal imidization were used to prepare PI-based monoliths in sequence. The hybridized PI (PI-co-POSS) monoliths exhibit potential in liquid diode application to achieve oil–water separation.

Molecular Weight and Gas Separation Performance of Polyimide Membrane: Insight into Role of Imidization Route

Various methods have been explored to improve the gas separation performance of polyimide membrane for more viable industrial commercialization. Generally, polyimide membrane can be synthesized via two different methods: chemical imidization and thermal imidization routes. Due to the markedly different membrane synthesis conditions, the influence of imidization methods on the gas transport properties of resulting membrane is worthy of investigation. The polyimide produced from two imidization methods was characterized for its molecular weight. In overall, the molecular weight of thermally imidized polyimide was higher than that of chemically imidized one except ODPA-6FpDA:DABA as it was prone to depropagation at high temperature. It was observed that the chemically imidized ODPA-6FpDA:DABA membrane possessed better gas separation performance than the thermally imidized counterpart. In particular, it showed 12 times higher CO2 permeability (19.21 Barrer) with CO2/N2 selectivity of 5. After crosslinking, the CO2/N2 selectivity of the polyimide membrane was further improved to 11.8 at 6 bar of permeation pressure.

Preparation of R-BABP Polyimide Fibers via Wet Spinning of Polyamide Acid

A polyamide acid (PAA) based on diamine 4,4'-bis (4-aminophenoxy) diphenyl and 1,3-bis (3',4-dicarboxyphenoxy) benzene dianhydride was synthesized. PAA fibers were obtained by wet spinning. Then, these fibers were converted into polyimide by thermal imidization. Dependence of the structure and properties of fibers on the die drawing and the composition of the coagulation bath was studied. It is shown that the composition of the coagulation bath has a significant effect on the morphology and mechanical properties of polyimide (PI) fibers. To obtain defect-free fibers, a coagulation bath consisting of ethylene glycol/ethanol at 50/50 vol. % was found to be optimal. An increase in the die drawing of fibers from 1 to 2 times leads to an increase in tensile strength and strain at break of the polyimide fibers.