1,2,4,5-Cyclohexanetetracarboxylic dianhydride (HPMDA, CAS number 2754-41-8) has a cyclohexane centre with two carboxylic anhydrides substituents sitting opposite to each other. HPMDA reacts with amines for polyimides or alternatively with alcohols for polyesters. The non-aromatic cyclohexane centre provides local excited state to the synthesized photochromic polyimides showing large contrast of the photo-switching effect (compared to fully aromatized polyimides). The polyimides derived from 1,2,4,5-cyclohexanetetracarboxylic dianhydride exhibit high proton conductivity (0.2 ± 0.01 S/cm at 298 K and 95% related humidity). Like other polyimides, the polyimides have excellent chemical and thermal resistance and are used in optical fibre claddings and substrates for microelectronics.HPMDA can be used to synthesize polyesters that have four branches (dianhydride is hydrolysed to four carboxylic acids) for multiple functionalities, such as biodegradability, bioimaging and photoactivity.

Semi-aromatic thermosetting polyimide resins containing alicyclic units

Semi-aromatic thermosetting polyimide resins containing alicyclic units were prepared by the polymerization of 1,2,4,5-Cyclohexanetetracarboxylic Dianhydride (HPMDA), aromatic diamines and nadic anhydride (NA) served as reactive capping agent. To obtain the homogeneous poly (amic ester) (PAE) matrix resins, the 2-methoxyethanol (EGME) was used to esterify HPMDA. As an important components of copper clad laminates, the interlayer dielectric materials play a crucial role as the structural and functional basis of integrated circuit boards. In recent years, with the rapid development of new-generation communication technology, the Signal propagation delay and propagation loss cannot be ignored at high frequency. In this paper, we first investigated the esterification of HPMDA and developed a new esterification reagent. Then a series of semi-aromatic thermosetting PI resins containing alicyclic units derived from 1,2,4,5-Cyclohexanetetracarboxylic Dianhydride, aromatic diamines are prepared by PMR method. Finally, the effects of alicyclic unit (HPMDA) and aromatic diamines on the properties of PI prepolymers and cured PI resins were investigated.[1]

Researchers successfully synthesized a series of semi-aromatic thermosetting PI resins derived from 1,2,4,5-Cyclohexanetetracarboxylic Dianhydride, aromatic diamines and NA by PMR method. The esterification of HPMDA was investigated and the EGME was employed for the first time to esterify HPMDA. The diamines containing alkyl group, trifluoromethyl group, and symmetric structure contribute to the preparation of uniform PAE resin, and the corresponding resins have low viscosities. Compared with the full-aromatic API-1 derived from 1,2,4,5-Cyclohexanetetracarboxylic Dianhydride and 3,4-ODA, the non-planar and non-conjugated structure of 1,2,4,5-Cyclohexanetetracarboxylic Dianhydride endows the obtained semi-aromatic B-stage resins with loose polymer chains packing and less through-bond conjugated electrons, which account for the low melt viscosities, good solubility and excellent dielectric properties. Moreover, PI-4 exhibits good overall performance, including Tg over 280?°C, good mechanical properties and low melt viscosity. These results suggest the potential application of the semi-aromatic PI-4 in high frequency circuit boards.

High Performance Soluble Polyimides from Ladder-Type

Recently, the demand of high-performance transparent polymer substrates increases dramatically with the rapid development of flexible electronics, especially for the flexible OLED displays. The 1,2,4,5-cyclohexanetetracarboxylic dianhydride (HPMDA) is widely used to prepare transparent PIs. However, the HPMDA-based PI films suffer from high CTE over 50 ppm K?1 and weak antioxidant capacity, and are prone to yellow stain under high temperatures. So, it is necessary to develop new dianhydride monomers to satisfy the urgent need of flexible OLED displays. Compared with the dianhydride 4,4′-(Hexaflouroisopropylidene) diphthalic anhydride (6FDA) and 1,2,4,5-Cyclohexanetetracarboxylic Dianhydride (HPMDA), the resulting polyimide (PI) films based on 8FDA exhibited an obviously higher glass transition temperature (Tg, 401 °C) and a much lower coefficient of thermal expansion (CTE, 14 ppm K?1). Herein, a rigid semi-alicyclic dianhydride 8FDA was developed to prepare high-performance, transparent PIs. The rigid structure of 8FDA was expected to increase the Tg and decrease the CTE at the same time.[2]

The solubility of films derived from 8FDA is as good as 6FDA and 1,2,4,5-Cyclohexanetetracarboxylic Dianhydride for given diamines. It can be explained that the rigid 8FDA monomer owned more linear, semi-alicyclic structures and CF3 groups, which disrupted the chain packing and reduced the interchain interaction.It was found that 8FDA-based PIs exhibited higher Tg values than the corresponding 6FDA-based and 1,2,4,5-Cyclohexanetetracarboxylic Dianhydride-based PIs films. It can be explained that molecular structure of 8FDA, which was bridged by multi-substitute 1,4-cyclohexadiene segment, was more planar and regular than 6FDA and HPMDA. In conclusion, a polymorphic dianhydride 8FDA and a transparent polyimide based on 8FDA were reported. The geometric configuration transition during the synthesis of 8FDA was traced using single crystal X-ray diffraction of the intermediate compounds. Compared with the widely used dianhydride 6FDA and 1,2,4,5-Cyclohexanetetracarboxylic Dianhydride, 8FDA-based transparent PI films showed much better thermal and dimensional stabilities. The new building block for transparent PIs is a promising key monomer toward the substrate for flexible OLEDs display.

Colorless Semi-Alicyclic Copolyimides with High Thermal Stability and Solubility

Herein, an alicyclic monomer 1,2,4,5-Cyclohexanetetracarboxylic Dianhydride (HPMDA), two fluorinated aromatic monomers, 2,2-bis(3,4-dicarboxyphenyl)hexafluoropropane dianhydride (6FDA) and 2,2’-bis(trifluoromethyl)benzidine (TFMB) were copolymerized for the fabrication of CPIs with high thermal stability and good solubility. One-pot solution polycondensation was used to synthesize CPIs with moderated molecular weight. The glass transition temperature increases from 332 to 352 °C with increasing 1,2,4,5-Cyclohexanetetracarboxylic Dianhydride content in the copolymers, while the thermal decomposition temperature is improved with increasing 6FDA content. These results indicate that the copolyimide films can be successfully utilized in the development of novel heat-resistant plastic substrates for the optoelectronic engineering applications.[3]

In conclusion, a series of CPI films with different mole ratio of HPMDA/6FDA were successfully obtained by copolymerizing of TFMB, 6FDA and 1,2,4,5-Cyclohexanetetracarboxylic Dianhydride through one-pot solution polycondensation and the relationship between the polymer components and their properties was investigated. Incorporation of alicyclic dianhydride into fluorinated polyimide improves the optical transparency and Tg of the resulting polyimides. Meanwhile, the drawback of low decomposition temperature of alicyclic polyimide was compensated with increasing fluorinated dianhydride content.

References

[1]Wang, Z. - H., Fang, G. - Q., He, J. - J., Yang, H. - X., & Yang, S. - Y. (2020). Semi - aromatic thermosetting polyimide resins containing alicyclic units for achieving low melt viscosity and low dielectric constant. Reactive and Functional Polymers, 146, 104411. https://doi.org/10.1016/j.reactfunctpolym.2019.104411

[2]Li F, Liu J, Liu X, Wang Y, Gao X, Meng X, Tu G. High Performance Soluble Polyimides from Ladder-Type Fluorinated Dianhydride with Polymorphism. Polymers (Basel). 2018 May 18;10(5):546. doi: 10.3390/polym10050546. PMID: 30966580; PMCID: PMC6415444.

[3]Lan Z, Li C, Yu Y, Wei J. Colorless Semi-Alicyclic Copolyimides with High Thermal Stability and Solubility. Polymers (Basel). 2019 Aug 7;11(8):1319. doi: 10.3390/polym11081319. PMID: 31394813; PMCID: PMC6723692.