A novel alicyclic dianhydride, 2R,5R,7S,10S-naphthanetetracarboxylic dianhydride (HNTDA), was prepared through the hydrogenation of tetramethyl 1,4,5,8-naphthalenetetracarboxylate, followed by deprotection and dehydration reactions. Single crystal X-ray diffraction results revealed that HNTDA possesses an irregular L-shaped architecture with one anhydride ring equatorial, and the other axial on the naphthane ring. Conventional one-step solution polycondensation of HNTDA with commercial diamines enabled the preparation of fully or semi-alicyclic polyimides with sufficient molecular weights. The properties of HNTDA-based polyimides were systematically characterized and compared with their counterparts based on 1S,2R,4S,5R-cyclohexanetetracarboxylic dianhydride (HPMDA). Dynamic mechanical thermal analysis, thermogravimetric analysis, thermal mechanical analysis, and tensile testing indicated that HNTDA-based polymers exhibit markedly higher thermal and mechanical properties compared with HPMDA-based ones. These improvements can be rationalized according to the rigid, bulky, fused naphthanetetracarboxydiimide moiety, and the pronounced inter- and intra-molecular interactions. Furthermore, HNTDA-based polyimides were colorless or pale-yellow, and displayed good optical transparency, although their cutoff wavelength values were higher than those of HPMDA-based ones.

In this study, three adamantane-containing diamines, i.e. 1,3-bis(4-aminophenyl) adamantane (ADMDA), 1,3-bis(3,5-dimethyl-4-aminophenyl) adamantane (DMADMDA) and 1,3-bis(fluoro-aminophenyl) adamantane (FADMDA), were successfully synthesized by Friedel–Crafts alkylation reactions between 1-adamantanol and acetanilide or its analogues, followed by hydrolysis with aqueous NaOH solution. Three regio-isomers were formed in the case of FADMDA due to the occurrence of both para- and ortho-alkylation (relative to the amino groups). Three series of semi-alicyclic polyimides were subsequently produced through a conventional one-step solution polycondensation between the as-developed diamines and commercial dianhydrides. The properties of the synthesized polyimides were characterized with respect to their thermal, mechanical and optical properties. The adamantane-containing polyimides exhibited significantly high glass transition temperatures (T_g) in the range 285–440 °C, excellent optical transparency (>80% transmittance at 400 nm) and optimal thermal and mechanical properties. The substituents in diamines significantly impacted the properties of the resulting polyimides. Specifically, the polyimides from DMADMDA demonstrated higher d-spacing, higher T_g, lower coefficient of thermal expansion (CTE), better optical properties and inferior tensile properties relative to the ADMDA-derived polymers, which could be attributed to the enhanced chain rigidity and reduced inter- and intra-molecular interactions associated with the two bulky methyl groups. In contrast, the FADMDA-derived polymers exhibited lower d-spacing, lower T_g, higher CTE, higher tensile modulus and lower elongation at break than the ADMDA-based ones, due to the reduced chain linearity regularity caused by the ortho-alkylated isomers, as well as suppressed intramolecular interaction originating from the strongly electron-withdrawing fluorine atoms. The excellent comprehensive properties of the adamantane-containing polyimides render these materials promising candidates for a variety of optical and optoelectronic applications.

Highly soluble phenylethynyl-endcapped isoimide oligomers were synthesized using 2,3,3′,4′-biphenyltetracarboxylic dianhydride (3,4′-BPDA) and aromatic diamines as the monomers, 4-phenylethynyl phthalic anhydride (4-PEPA) as the end-capping reagent, and trifluoroacetic anhydride as the dehydrating agent; then high performance thermosetting polyimides and composites were produced from these oligomers via the thermal crosslinking reaction of the phenylethylnyl group and the material properties were fully investigated. A series of isoimide oligomers with different molecular weights and a variety of chemical architectures were prepared by polycondensation of 3,4′-BPDA, 4-PEPA, and aromatic diamines including m-phenylenediamine (m-PDA), 2,2′-bis(trifluoromethyl)benzidine (TFMB), and 3,4′-oxydianiline (3,4′-ODA), followed by cyclization with trifluoroacetic anhydride. These isoimide oligomers were characterized by means of gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), rheological measurements, intrinsic viscosity measurement, and solubility tests. Compared to their imide analogues, isoimide oligomers showed much higher solubility in low boiling point solvents, and slightly lower melt viscosity, which can be attributed to their unique asymmetric architecture. These resins were formulated into thermosetting polyimides and composites by thermal crosslinking of the phenylethynyl group and conversion from isoimide to imide at elevated temperatures. The properties of the thermosets and composites were studied using mechanical property measurements, dynamic mechanical thermal analysis (DMTA), and thermogravimetric analysis (TGA). The cured polyimides exhibited extremely high glass transition temperatures (T_g) up to 467 °C, and 5% weight loss temperatures (T_5%) up to 584 °C in a nitrogen atmosphere. The polyimide/quartz fiber composites possessed excellent high temperature mechanical properties due to the high glass transition temperatures of matrix resins.