Xiang-Dan Li

Photocrosslinking of sulfonated poly(arylene ether sulfone) in a swollen state

Novel photocrosslinkable sulfonated poly(arylene ether sulfone)s containing chalcone moieties in the polymer backbone (SPAEF) were synthesized from 4,4′-dihydroxychalcone (4DHC), 4,4′-difluoro-diphenylsulfone-3,3′-disulfonate (SDFDPS) and decafluorobiphenyl (DFBP). We introduced a new strategy to crosslink photosensitive polymer electrolyte membranes by UV irradiation in a swollen state in order to preserve the interconnected hydrophilic channels in the hydrated SPAEF electrolyte membrane. Photocrosslinked membranes showed desired effects of improved mechanical properties with significantly low methanol diffusion coefficient, while maintaining high proton conductivity. SPAEF membranes after the photocrosslinking exhibited a proton/methanol selectivity of 7.6 × 105 S s cm−3 at 30 °C, which is 21 times higher than that of Nafion® 117. This novel photocrosslinking strategy also improved oxidative and hydrolytic stabilities of polymer membranes which are desirable for direct methanol fuel cell application.

Reducing driving voltage and securing electro-optic reliability of in-plane switching liquid crystal display by applying polysulfone photoalignment layer with photo-reactive mesogens

Newly synthesised photocurable polysulfone (PSCMh) was applied as a photoalignment layer of in-plane switching liquid crystal display (IPS LCD). When the linear polarised ultraviolet light (LPUVL) was irradiated on the typical calamitic nematic liquid crystals on the PSCMh alignment layer, the liquid-crystal director was aligned perpendicular to the LPUVL. Based on the experimental results, it was realised that IPS LCD photoaligned by PSCMh with additional polymer layer associated with reactive mesogen (RM) showed a low driving voltage with reduction of 0.2 V compared to the rubbed cell and also excellent electro-optic reliability such as alignment stability, residual direct current and voltage holding ratio compared to the purely photoaligned cell. Therefore, it was concluded that the polymer stabilisation of PSCMh with RM was effective for improving IPS LCD performances.

Carbon nanotube-induced morphological transformation for toughening of benzoxazole-containing semi-crystalline polyimide

Carbon nanotube (CNT)/semi-crystalline polyimide (PI) nanocomposites have been prepared by incorporating different concentrations of carboxylic acid-functionalized multi-walled CNTs. The incorporation of CNTs not only results in remarkable strength improvement, but also increases the toughness of nanocomposites. The toughness shows a maximum at the CNT concentration of 0.75 wt%, about twofold increment in toughness compared to neat PI. To explore the origin of this toughening behaviour, dispersion of nanotubes in the PI matrix and their interfacial interactions were investigated by TEM, FT-IR spectroscopy and UV-visible absorption spectroscopy, respectively. Morphological transformation of the crystalline phase induced by CNTs was monitored by polarized optical microscopy and WAXD. The fracture surfaces of CNT reinforced PI nanocomposites were investigated by SEM. It was suggested that the abrupt change of toughness with respect to CNT weight fraction is attributed to the percolation effects and concomitant morphological change, which was accounted for by a proposed model for nanotube-induced morphological transformation. The model provides novel insight into the design of strengthened and toughened materials by tailoring the structure at the nanoscale.

Synthesis and characterization of photosensitive poly(imide sulfonates) for fuel cell application

The novel sulfonated polyimide membranes were successfully synthesized by thermal imidization with monomers of 4,4′-(hexafluoroisopropylidene)diphthalic anhydride (6FDA), 4,4′-diaminodiphenyl ether-2,2′-disulfonic acid (SODA) and 3,3′-diaminochalcone (3DAC). Photosensitive chalcone moiety was introduced to the main chain of copolymers, and the photocrosslinking of resulting copolymer in aqueous electrolyte was attempted. A series of sulfonated copolyimide precursors containing chalcone functional groups in the main chain were prepared with different sulfonation degrees by controlling the molar ratio of SODA, 6FDA and 3DAC. The polymer membranes were prepared from these sulfonated aromatic precursors by solution casting and subsequent thermal imidization. The crosslinking with UV irradiation was attempted in the presence or absence of distilled water. The characterizations of the resulting membrane such as the ion-exchange capacity, water absorption and ionic conductivity were performed with respect to the copolymer compositions and the photocrosslinking conditions.

Synthesis, characterization and olefin polymerization behaviors of phenylene-bridged bis-β-carbonylenamine binuclear titanium complexes

Binuclear and multinuclear complexes have attracted much attention due to their unique catalytic performances for olefin polymerization compared with their mononuclear counterparts. In this work, a series of phenyl-bridged bis-β-carbonylenamine [O−NSR] (R = alkyl or phenyl) tridentate ligands and their binuclear titanium complexes (Ti2L1–Ti2L5) were synthesized and characterized by 1H NMR, 13C NMR, FTIR and elemental analysis. The molecular structure of ligand L2 (R = nPr) and its corresponding Ti complex Ti2L2 were further investigated by single-crystal X-ray diffraction, which showed that each titanium coordinated with six atoms to form a distorted octahedral configuration along with the conversion of the ligand from β-carbonylenamine to β-imino enol form. Under the activation of MMAO, these complexes catalyzed ethylene polymerization and ethylene/α-olefin copolymerization with extremely high activity (over 106 g mol (Ti)−1 h−1 atm−1) to produce high molecular weight polyethylene. At the same time, wider polydispersity as compared with the mononuclear counterpart TiL6 was observed, indicating that two active catalytic centers may be present, consistent with the asymmetrical crystal structure of the binuclear titanium complex. Furthermore, these complexes possessed better thermal stability than their mononuclear analogues. Compared with the complexes bearing alkylthio sidearms, the complex Ti2L5 bearing a phenylthio sidearm exhibited higher catalytic activity towards ethylene polymerization and produced polyethylene with much higher molecular weight, but with an appreciably lower 1-hexene incorporation ratio. Nevertheless, these bis-β-carbonylenamine-derived binuclear titanium complexes showed much higher ethylene/1-hexene copolymerization activity and 1-hexene incorporation ratios as compared with the methylene-bridged bis-salicylaldiminato binuclear titanium complexes, and the molecular weight and 1-hexene incorporation ratio could be flexibly tuned by the initial feed of α-olefin commoners and catalyst structures.

Characterizations of Photo-Alignable Multi-Functioning Polyimide Material

For a potential application in thin-film-transistor liquid crystal display (TFT-LCD) manufacturing as a multi-functioning layer working as an overcoat layer and LC alignment layer simultaneously, a novel chloromethylated polyimide was synthesized. The electrical performances of liquid crystal (LC) cells with chloromethylated polyimide alignment layers were investigated. The polymer layer acted as a multifunctional layer that does role of planarization layer and photo-alignment layer with high photosensitivity and excellent thermal stability, simultaneously. The capacitance-voltage characteristics of LC cells fabricated from the photo-aligned layers were measured. The LC cells with rubbed and photo-aligned layer showed higher residual DC values and corresponding lower voltage holding ratios compared to the commercial alignment layer, probably due to the photo-induced ionic charges on the alignment layer. Mechanical rubbing of the extensively purified polymer layer did not generate much difference in residual DC when compared to commercial polyimides.