Xueliang Pei

Preparation and characterization of poly(imide siloxane) block copolymers based on diphenylthioether dianhydride isomer mixtures

A series of poly(imide siloxane) block copolymers were prepared based on diphenylthioether dianhydride isomer mixtures (m-TDPA), 4,4′-oxydianiline (ODA) and bis(γ-aminopropyl)polydimethylsiloxane (APPS). The ODA and m-TDPA composed the hard segment, while the APPS and m-TDPA composed the soft segment. The hard segment length was kept constant, while the soft segment lengths were varied with varying the APPS contents. The copolymers had inherent viscosities range from 0.37 to 0.51 dL g−1, and their weight-average molecular weights and number-average molecular weights were in the range of 45 000–52 600 and 21 300–27 000, respectively. All copolymers were readily soluble in many organic solvents, and could afford flexible films via solution casting. The cast films exhibited mechanical properties with tensile strengths at break of 26.7–86.2 MPa, elongations at break of 9.9–112.2%, and tensile moduli of 0.12–2.15 GPa, depending on the soft segment length. The films also exhibited low water uptakes in the range of 0.18–0.68 wt.%. Furthermore, the copolymers showed high glass transition temperatures derived from the hard segments in the range of 196–225 °C, and good thermal stability with almost no weight loss up to 350 °C under nitrogen atmosphere and 335 °C under air atmosphere.

Comparative studies on melt processable polyimides derived from 2,3,3',4'-oxydiphthalic anhydride and 2,3,3',4'-thioetherdiphthalic anhydride

Two thermoplastic polyimides were controllably synthesized with similar molecular weight from 2,3,3′,4′-oxydiphthalic anhydride (3,4′-ODPA) or 2,3,3′,4′-thioetherdiphthalic anhydride (3,4′-TDPA) with 4,4′-diaminodiphenyl ether (ODA) by a one-step method of m-cresol. The solubility and mechanical properties of these polymers were investigated for comparison. The thermal and melt processable properties of these polymers were examined carefully by differential scanning calorimetry, thermogravimetric analysis (TGA), rheometer and melt index, and so on. It was found that the glass transition temperature (Tg) of 3,4′-TDPA/ODA was about 15°C lower than that of 3,4′-ODPA/ODA, the melt indices of 3,4′-TDPA/ODA at different temperatures were higher than those of 3,4′-ODPA/ODA, while the minimum melt viscosity of 3,4′-TDPA/ODA was lower than those of 3,4′-ODPA/ODA. Furthermore, TGA results showed that 3,4′-TDPA/ODA had different degradation mechanism in air compared with 3,4′-ODPA/ODA. The long-term thermooxidative stability results showed that 3,4′-TDPA/ODA had better thermal oxidative stability than 3,4′-ODPA/ODA at 410°C for 6 h in air, which could be associated with the results of apparent activation energy (Ea) of polymers calculated by TGA dynamics. The natural bond orbital charge of ethero atoms (S or O), and energy gap of the corresponding model compounds were also obtained by computational simulation to correlate with polymer properties.

Comparative study on polyimides derived from isomeric diphenylsulfonetetracarboxylic dianhydrides

In this study, three diphenylsulfonetetracarboxylic dianhydride (DSDA) isomers namely 2,2′,3,3′-DSDA (3,3′-DSDA), 2,3,3′,4′-DSDA (3,4′-DSDA) and 3,3′,4,4′-DSDA (4,4′-DSDA) were prepared from the corresponding diphenylthioethertetracarboxylic dianhydride isomers. Based on the three DSDA isomers, a series of isomeric polyimides were prepared. The properties, such as film-forming ability, solubility, wide-angle x-ray diffraction, thermal and mechanical properties as well as rheological behavior, were compared among the isomeric polyimides. It was found that 4,4′-DSDA-based polyimides had much better film-forming ability than 3,3′-DSDA- and 3,4′-DSDA-based polyimides. 3,4′-DSDA-based polyimides had better solubility than 3,3′-DSDA- and 4,4′-DSDA-based polyimides. Furthermore, for a given diamine, the glass transition temperatures of the polyimides from the three DSDA isomers decreased in the order of 3,3′-DSDA > 3,4′-DSDA > 4,4′-DSDA, while the 5% weight loss temperatures in both air and nitrogen atmospheres of the polyimides mainly increased in the order of 3,3′-DSDA < 3,4′-DSDA < 4,4′-DSDA. Moreover, 3,4′-DSDA- and 4,4′-DSDA-based polyimides showed much better melt stability than 3,3′-DSDA-based polyimide.

The friction and wear properties of carbon nanotubes/graphite/carbon fabric reinforced phenolic polymer composites

In this paper, either graphite (Gr) or carbon nanotubes (CNTs), or both of them were incorporated into carbon fabric reinforced phenolic (CFRP) composites, preparing by a dip-coating and heat molding process, the tribological properties of the resulting composites were investigated using a block-on-ring arrangement. The worn surfaces were observed by scanning electron microscope to understand the mechanism. Experimental results showed that the optimal Gr was more beneficial than CNTs in improving the tribological properties of the CFRP composites when they were singly incorporated. It is well worth noting that the friction and wear behavior of the CNTs-filled CFRP composites were improved further when Gr was added, indicating that there is a synergistic effect between them. Tribological tests under different sliding conditions revealed that the Gr and CNTs-filled CFRP composites seemed to be the most suitable for tribological applications under higher sliding speed and load, and oil lubrication.

Hydrophobic modification of poly(aryl ether ketone ketone) aerogel via poly(dimethylsiloxane)

Property and structure of aerogels with polar groups almost suffer from their high hydrophilicity. In this study, in order to improve the hydrophobicity of poly(aryl ether ketone ketone) aerogel prepared from poly(aryl ether ketone ketone) containing trimethoxysilane side groups, hydroxy-terminated poly(dimethylsiloxane) was added. During gelation, hydroxy-terminated poly(dimethylsiloxane) condensed with the methoxy groups or the hydrolyzed methoxy groups of the trimethoxysilane side groups. It was found that the hydrophobicity of poly(aryl ether ketone ketone) aerogel improved significantly even though only 5 wt% hydroxy-terminated poly(dimethylsiloxane) was added, and the hydrophobicity of the modified poly(aryl ether ketone ketone) aerogel showed an increase trend with increasing the content of hydroxy-terminated poly(dimethylsiloxane).Graphical Abstract

A multiscale hydrothermal carbon layer modified carbon fiber for composite fabrication

A novel multiscale hydrothermal carbon layer (MHTCL) for carbon fiber (CF) surface modification was developed. The MHTCL is a multiscale high-disorder amorphous carbon coating with a colored appearance, abundant functional groups, multiscale roughness, a large specific surface area, a high surface energy, and good wetting ability. The O/C atom ratios of the MHTCL-modified CF were in the range of 0.17–0.23, and the functional groups were mainly C–O and CO groups. During the low-concentration glucose hydrothermal treatment with the carbon fibers (CFs), the glucose generates furan derivative intermediates, which adsorb on the surface of the CFs and carbonize continuously, finally forming the MHTCL on the CFs. The fracture and rupture of the MHTCL during the forming process produce new nucleation centers on the CF surface, which result in abundant multiscale irregular particles. The MHTCL is a facile method for the modification of CFs. The fabrication of the CF composites demonstrated that the MHTCL obviously increases the interlaminar shear strength of the CF/polyimide composite and the interfacial interaction of the CF and polyetheretherketone.