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We studied the interfacial shear strength (IFSS) in carbon fiber (CF) and special engineering plastics matrix, with an emphasis on the effect of the functional group in the matrix. The IFSS was analyzed to quantify the interfacial adhesion between the fiber and the matrix. To obtain the apparent IFSS of the composites, microdroplet test was measured at single-fiber composites. Results of the microdroplet test displayed that the apparent IFSS in the composites was directly determined by their inherent surface properties and the functional groups in the matrix. Compared with other matrices, polyetherimide (PEI) exhibited relatively strong mechanical bonding and interfacial adhesion, showing that the imide groups had good interfacial compatibility with the pristine CF surface. Based on the results of this study, polymers containing imide groups were one of the best candidates for sizing agent of CF used as reinforcement of high-temperature thermoplastics.

In this work, 4,4′-isopropylidenedicyclohexanol (HBPA)-based dinitro isomers mixture (H″BPBN and H′BPBN) was synthesized and separated, and the structures of dinitro isomers were confirmed by differential scanning calorimetry and proton nuclear magnetic resonance spectroscopy. A series of copolyimides were prepared from diamino monomers with different percentages of novel diamine H″BPDA and 4,4′-(hexafluoroisopropylidene) diphthalic anhydride via a conventional two-step procedure. All the copolyimides could afford flexible, tough, and transparent films with transmittance no less than 73% at 450 nm, which was attributed to the fact that nonplanar alicyclic diamine and the bulky and weakly polarizable trifluoromethyl hampered the formation of charge-transfer complex. Moreover, all the copolyimides were soluble not only in polar solvents such as N,N-dimethylformamide but also in low-boiling-point solvents such as dichloromethane, which was related to the fact that the existence of alicyclic diamine and bulky trifluoromethyl decreased the intermolecular force. In addition, the conformation effects of H″BPDA and H′BPDA on the aspects of thermal, mechanical, optical, and soluble performance of copolyimides were investigated and their structure–property relationships were discussed in detail.

In this work, the surface modification of short carbon fibers (SCFs) using polyimide (PI) as a sizing agent was conducted and fully characterized, and SCF-reinforced polyether ether ketone (PEEK) composites were obtained by extrusion and injection molding. The surface characteristics of the PI-coated SCFs were evaluated using scanning electron microscopy and X-ray photoelectron spectroscopy. The results indicated that a uniform PI sizing layer was formed on the surfaces of the SCFs. Thermogravimetric analysis results demonstrated that PI-coated SCFs had better thermal stability than commercial SCFs. The tensile strength and flexural strength of the PI-coated SCF/PEEK composites showed improvements of 11.8% and 16.6% compared with the commercial cases, which were attributed to the PI sizing treatment effectively improving the interfacial adhesion between the SCF and the PEEK matrix. Dynamic mechanical analysis and the morphologies of tensile fracture surfaces suggested better interfacial adhesion between the fibers and the PEEK matrix, which were in good agreement with the mechanical properties. Due to the convenient processing of PI sizing as well as the effectively improved mechanical properties of the composites, the PI-sizing methodology has great potential application in the field of fiber-reinforced high-temperature engineering plastics composites.

In order to obtain colorless and soluble polyimide films, a dianhydride containing 1,4:3,6-dianhydro-d-mannitol unit, 2,5-bis(3,4-dicarboxyphenoxy)-1,4:3,6-dianhydromannitol dianhydride (IMDA) was synthesized. And a series of copolyimides were prepared from IMDA, 1,2,4,5-benzenetetracarboxylic anhydride (PMDA), and 4,4′-oxydianiline by adjusting the mole fraction (between IMDA and PMDA) of IMDA from 0% to 100%. It was found that the solubility as well as the transmittance of the copolyimide films enhanced with the increased content of IMDA. Especially, when the content of IMDA was 60% or more, the copolyimides were readily soluble in common polar solvents and could afford flexible, tough, and colorless films with transparency up to 84% at 450 nm, which may be ascribed to the incorporation of the relatively twisted and flexible 1,4:3,6-dianhydro-d-mannitol units into the backbone of copolyimides. Additionally, the influence of IMDA on the thermal, mechanical, and morphological properties of copolyimides was investigated.

A novel hydrophilic polyamide, PA-OH containing 1:4;3:6-dianhydro-d-mannitol (isomannide) fragment was synthesized and used as an additive to prepare a series of polyethersulfone (PES)/PA-OH hybrid membranes with different content of PA-OH by phase separation method. And the addition of PA-OH was expected to improve the hydrophilicity, permeability, and antifouling performance of the PES ultrafiltration (UF) membrane. The scanning electron microscopic and atomic force microscopic images showed that the addition of PA-OH greatly changed the morphology of membranes by increasing the porosity, pore size and pore density, and the hydrophilicity was also improved with the increased PA-OH content. Based on the UF experiment, when the PA-OH content was 3%, the fluxes of pure water and bovine serum albumin solution reached 213.1 and 92.6 L m−2 h−1, which were close to 1.5 times and 2 times those of the bare PES membrane, respectively. When the PA-OH content was 5%, the FRR1st reached 85.2%, which was distinctly higher than that of the compared PES/polyethylene glycol5% hybrid membrane of 74.3%. And the FRR2st of the PES/PA-OH5% hybrid membrane was still over 80%, which indicated its long-term antifouling performance. Thus, the PA-OH can be a candidate for the hydrophilic additives.

Two kinds of polyarylates with diphenylamine-fluorene units were synthesized from the bisphenol monomer “ N, N-di(4-hydroxyphenyl)-2-amino-9,9-dimethylfluorene” with two different benzenedicarbonyl chlorides. These polyarylates were highly soluble in N, N-dimethylacetamide, tetrahydrofuran, and chloroform and could be easily solution-cast into transparent films. Both of the polyarylates exhibited a couple of reversible redox with half-wave potentials in the range of 0.87–0.90 V. During the electrochromic process, the color of the film changed from colorless (neutral state) to grey green (oxidation state) with a high coloration efficiency of 242 cm2 C−1. Compared with the polyarylates prepared from terephthaloyl chloride, the polyarylates prepared from isophthaloyl chloride exhibited enhanced fluorescence because of the reduced charge-transfer effect. Furthermore, its fluorescence could be reversibly switched under the applied potentials.

Two series of 10% polytetrafluoroethylene (PTFE)/polyether ether ketone (PEEK) composites reinforced with potassium titanate whisker (PTW/PTFE/PEEK) and chopped glass fiber (GF/PTFE/PEEK) were prepared and characterized. We investigated the effects of the additives on thermal stability, tribological properties, mechanical properties, and rheological behavior. The results illustrated that the mechanical properties of 10% PTFE/PEEK blend can be dramatically improved by incorporating either PTW or GF; however, the reinforcing effect of GF was found to be superior. It was found that 1% additive resulted in blends with the best tribological properties. Compared to the unmodified blend, the friction coefficient and wear rate of the 1% PTW blend decreased by 7.2% and 21%, respectively, while the corresponding values of 1% GF blend decreased by 0.66% and 51%, respectively.

In order to prepare novel polyimides (PI) with high transparency and solubility in common solvents, three diamine monomers containing pyridine or methyl-substituted pyridine and cyclohexane, 1,1′-bis[4-(5-amino-2-pyridinoxy)phenyl]cyclohexane (IIIa), 1,1′-bis[4-(5-amino-3-methyl-2-pyridinoxy)phenyl]cyclohexane (IIIb), and 1,1′-bis[4-(5-amino-2-methyl-6-pyridinoxy)phenyl]cyclohexane (IIIc), were synthesized and characterized. The diamine monomer (IIIa) was subsequently polymerized with 3,3′,4,4′-oxydiphthalic anhydride, 4,4′-(hexafluoroisopropylidene)-diphthalic anhydride (6FDA) to obtain PIs, PI-1 and PI-2. Furthermore, PI-3 (IIIb/6FDA) and PI-4 (IIIc/6FDA) were prepared for structure–property comparison studies. The structures of the resulting PIs were characterized by fourier transform infrared spectroscopy (FT-IR), X-ray diffraction, and elemental analysis. The physical properties of the PI films were investigated by thermogravimetric analysis, differential scanning calorimetric analysis, dynamic mechanical analysis, and ultraviolet–visible spectroscopy. In general, the PIs showed excellent thermal properties and good mechanical properties. Most had good solubility in polar organic solvents such as N, N-dimethylacetamide, N, N-dimethylformamide, N-methylpyrrolidone (NMP), m-cresol, and even soluble in low boiling solvents such as tetrahydrofuran (THF) and CHCl3. The PI films also exhibited high optical transmittance of 94–97% at 500 nm and cut-off wavelength at 345–359 nm. In summary, the introduction of methyl, cyclohexane, and pyridine groups into the backbone was shown to improve the solubility and transparency of PI films.

A series of novel polyimides (PIs) based on N,N-di(4-aminophenyl)-2-amino-9,9-dimethylfluorene and various dianhydrides were synthesized. These PIs were amorphous and readily soluble in many solvents. They displayed outstanding thermal stability and high glass transition temperatures (269–374°C). The polymer films showed reversible electrochemical redox and satisfactory electrochromic performance with long-term stability, high coloration efficiency, and acceptable switching times. The PI derived from 1,2,4,5-cyclohexanetetracarboxylic dianhydride exhibited maximum fluorescence at 400 nm with quantum yields up to 28.1%. Furthermore, the fluorescence can be effectively electroswitched between “on” and “off” states, exhibiting a high contrast ratio of 75.

A phenylethynyl-terminated imide oligomer (PETI)was prepared from a triamine and 4-phenylethynylphthalic anhydride. The oligomer can be used to prepare high performance resin-based composite material via resin transfer moulding due to its low melt viscosity. The cured resin also exhibited excellent thermal stability with 5% weight loss at temperature above 531°C and higher glass transition temperature Tg (410°C) than PETI series as a result of the introduction of star-branched units. The rheological properties of the oligomer were measured and numerically fit with the dual Arrhenius model. The curing of the resin was also studied by dynamic and isothermal differential scanning calorimetry measurements. Based on the experimental data, both the curing reaction rate and the curing degree were calculated in the dynamic mode and tested under isothermal conditions.

A series of autophotosensitive semiaromatic hyperbranched polyimides (PIs) were prepared by (A2 + B3)-type method and endcapped with 2,6-dimethylaniline. The photosensitive hyperbranched PIs (PHBPIs) showed excellent solubility, excellent optical properties, and low birefringences in the range of 0.0022–0.0042 caused by their special hyperbranched structures and alicyclic chain segments reduced both intramolecular and intermolecular charge transfer complex effect. It also showed excellent mechanical properties with tensile modulus in the range of 1.37–1.60 GPa and good thermal stabilities. Photolithographic property of the polymer was examined by ultraviolet exposure. Scanning electron microscopic analysis revealed a highly resolved pattern with a line width of 8 μm.

Pyridazine-containing aromatic diamine monomer, 3,6-bis(4-aminophenoxy)pyridazine (APPD), was successfully synthesized by a nucleophilic substitution reaction of 3,6-dichloropyridazine with para-aminophenol. The aromatic heterocyclic diamine was employed to synthesize a series of polyimides (PIs) by polycondensation with various commercially available aromatic dianhydrides in N, N-dimethylacetamide via the conventional two-step method and further thermal imidization forming polyimides. The inherent viscosities of the resulting poly (amic acid)s were in the range of 0.47–1.51 dL g−1. Meanwhile, strong and flexible PI films were obtained, which had good thermal resistance, with the glass transition temperatures of 214–305°C and the temperature at 5% weight loss of 421–463°C under nitrogen atmosphere, as well as outstanding mechanical properties with tensile strengths of 61–102 MPa and elongations at break of 2.8–64.7%. The cutoff wavelength of the PI films were ranged in 357–413 nm.

Thermal expansion behavior of polyimide (PI) films based on benzoxazole containing diamine, 5,4′-diamino-2-phenyl benzoxazole (DAPBO), was investigated systematically. Effects of preparation parameters on the values of in-plane coefficient of thermal expansion (in-plane CTE) were studied from the viewpoint of film thicknesses, curing rates, and substrates. It was found that the in-plane CTE values increased as a function of film thicknesses and curing rates, this pattern was also applicable to PI based on DAPBO and pyromellitic dianhydride (PMDA), which showed negative in-plane CTE value. The influence of preparation parameters on in-plane CTEs was interpreted by the effect of residual solvent. Thermogravimetric and dynamic mechanical analyses were used to study the curing process of poly(amic) acid films with various amounts of residual solvent and further to illustrate the effect of residual solvent on in-plane CTE values. In-plane and out-of-plane CTE of PI film based on DAPBO and 3,3′,4,4′-oxydiphthalic dianhydride (ODPA) were directly measured using thermomechanical analysis instrument, and the values were 22.5 and 62.3 ppm K-1, respectively, indicating the orientation character of PI chains along the film plane direction.

A series of polyimide (PI) films were prepared from a diamine-containing benzoxazole unit (5,4′-diamino-2-phenyl benzoxazole) and five dianhydrides via two-step polymerization process. The PI films showed outstanding mechanical properties with tensile modulus up to 7.3 GPa without preorientation process. According to the results of thermal analysis, the glass transition temperature of the films was up to 412°C, and the films showed good thermodimensional stability. Thermal analysis and wide-angle x-ray diffraction analysis revealed that the PIs were semicrystalline. Excellent properties of these PIs were attributed to the benzoxazole group in the main chain and accordingly to the rigid-rod structure and high level of linearity of the polymer backbones. These results correlate with each other and contribute to our overall understanding of the effects of benzoxazole moiety on the properties of the PI films.

A series of autophotosensitive semiaromatic hyperbranched polyimides were prepared by (A2 + B3)-type method and endcapped with 3-aminophenylacetylene. The photosensitive-hyperbranched polyimides (PHBPIs) showed excellent solubility, excellent optical properties, and low birefringences in the range of 0.0010–0.0027, caused by their special hyperbranched structures and alicyclic chain segments reduced both intramolecular and intermolecular charge transfer complex effect. The cured films also showed high glass transition temperatures between 204°C and 220°C, excellent thermal stabilities with 10% thermal decomposing temperatures in the range of 476–495°C, and good mechanical properties. The PHBPIs had photosensitivities ( Dg) in the range of 80–162 mJ/cm2 and showed a clear negative image with a line width of 8 µm when exposed to an ultraviolet light of 365 nm ( i-line).