Jianfeng Ban

Synthesis and phase behavior of mesogen-jacketed liquid crystalline polymer with triphenylene discotic liquid crystal mesogen unit in side chains

A novel mesogen-jacketed liquid crystalline polymer (MJLCP) containing two triphenylene (Tp) units in the side chains, named poly[bis(3,6,7,10,11-pentakis(hexyloxy)triphenylen-2-yl)2-vinyl terephthalate] (PBTCS), was designed and successfully synthesized via conventional free radical polymerization. The chemical structure of the monomer was confirmed by 1H/13C NMR and high-resolution mass spectrometry. The molecular characterization of the polymer was performed with 1H NMR, gel permeation chromatography (GPC) and thermogravimetric analysis (TGA). The phase structure and transition of the polymer were investigated by the combination of techniques, including differential scanning calorimetry (DSC), polarizing optical microscope (POM), 1D/2D wide-angle X-ray diffraction (1D and 2D WAXD) and 1D small-angle X-ray scattering (1D SAXS). The results showed that the PBTCS reached a relatively high glass transition temperature and formed a higher symmetry hexagonal columnar (ΦH) phase due to the strong coupling effect between the Tp moieties and the MJLCP main chain.

Influence of the spacer and molecular weight on the phase behavior of side-chain liquid crystalline polymers containing triphenylene discotic mesogen units as side groups

Two series of side chain liquid crystalline polymers (SCLCPs), poly{[3,6,7,10,11-pentakis(hexyloxy)-2-oxytriphenylene]methacrylate} (PMTS with no flexible spacer) and poly{6-[3,6,7,10,11-pentakis(hexyloxy)-2-oxytriphenylene]hexyl methacrylate} (PMT6S with 6 methylene units as a flexible spacer), with different molecular weights (Mn) and low molecular weight distributions have been successfully synthesized via atom transfer radical polymerization (ATRP). The phase behavior of the polymers has been investigated by a combination of techniques, including differential scanning calorimetry (DSC), polarized optical microscopy (POM), and 1D and 2D wide-angle X-ray diffraction (1D and 2D WXRD). The experimental results revealed that the LC phase structures of PMTS were found to be strongly Mn dependent. The PMTS polymers were amorphous when the Mn was lower than a critical Mn of approximately 2.03 × 104 g mol−1. When the Mn was higher than this critical value, the PMTS polymers displayed a rectangular (ΦR) columnar phase. On the contrary, the PMT6S polymers displayed a higher symmetry hexagonal (ΦH) columnar phase, which was independent of Mn. A comparison between PMTS and PMT6S suggested that the spacer plays an important role in the construction of liquid crystalline (LC) ordered structures. For the former, PMTS polymers without the spacer formed rectangular ΦR phases caused by the Tp moieties and the main chain as a whole, due to the strong coupling effect between the Tp moieties and the main chain. For the latter, PMT6S polymers with 6 methylene units as a flexible spacer gave a higher symmetry ΦH phase owing to the decoupling and self-organization of the Tp moieties.

Synthesis and liquid crystalline behavior of side chain liquid crystalline polymers containing triphenylene discotic mesogens with different length flexible spacers

A series of side chain liquid crystalline polymers (SCLCPs) containing triphenylene (Tp) units in the side chains, denoted as PMTS (without spacer) and PMTnS (n = 2, 3, 4, 6, which is the number of the methylene units between the main chain and Tp moieties in the side chains), with different lengths of spacers were synthesized through conventional free radical polymerization. The chemical structures of the monomers were confirmed by 1H/13C-NMR, and the phase behaviors were examined by differential scanning calorimetry (DSC), polarized optical microscopy (POM) and wide-angle X-ray diffraction (1D and 2D WAXD). The molecular characterization of the polymers was performed with 1H-NMR, gel permeation chromatography (GPC) and thermogravimetric analysis (TGA). The phase behaviors of the polymers have been investigated by a combination of techniques including DSC, POM, 1D and 2D WAXD. The results showed that the length of spacer has significant effects on the LC phase behavior of polymers. For PMTS and PMT2S, they displayed the columnar phase developed by the Tp moieties and the main chain as a whole due to the strong coupling effect of the Tp moieties and the main chain. For the PMT3S, PMT4S and PMT6S, they formed the symmetry hexagonal columnar (ΦH) phase owing to the decoupling effect. All of these indicated that the “decoupling effect” or “coupling effect” depended on the length of spacers, leading to the different LC phase formation mechanism.

Thermomechanical Properties and Morphology of Liquid Crystalline Polyurethane/Epoxy Resin Composites

One new kind of epoxy resin toughening agent defined as liquid crystalline polyurethane elastomers (LCPUE) containing mesogenic ester groups and trithylene glycol flexible chain was synthesized and its nematic structure was observed by POM and XRD. The LCPUE was to modify the epoxy resin (E-51). The mechanical properties, fracture surface morphology, and thermal properties of the E-51/LCPUE curing system were systematically investigated. Experimental results revealed that the impact strength of the epoxy resin modified with LCPU is 1.9 times higher than that of the unmodified system, enhanced the thermal decomposition temperature by about 12 °C, and the fracture surfaces all modified systems display tough fracture feature.

Preparation and Characterization of Liquid Crystalline Polyurethane/Al2O3/Epoxy Resin Composites for Electronic Packaging

Liquid crystalline polyurethane (LCPU)/Al2O3/epoxy resin composites were prepared by using LCPU as modifier. The mechanical properties, thermal stability, and electrical properties of the LCPU/Al2O3/epoxy resin composites were investigated systematically. The thermal oxidation analysis indicated that LCPU/Al2O3/epoxy resin composites can sustain higher thermal decomposition temperature. Meanwhile, coefficient of thermal expansion (CTE) was also found to decrease with addition of LCPU and nano-Al2O3.

Synthesis and Characterization of Biphenylnate Liquid Crystalline Polyurethanes

A series of novel biphenylnate liquid crystalline polyurethanes (BLCPs) were synthesized by polyaddition reaction of 4,4’-dihydroxybiphenyl with 2,4-TDI(2,4-toluenediisocyanate) and diethylene glycol through changing the molar ratio of diphenol and diol. The thermotropic properties, the melting point (Tm) and the isotropization temperature (Ti) of the synthesized polyurethanes were characterized by FT-IR, DSC, POM and WXRD. The results of experiments showed that all of the polyurethane polymers exhibited thermotropic liquid crystalline properties between 130°C and 230°C. The transition temperature (Tm and Ti) decreased with an increase in the length of the flexible chain.

Synthesis of thermotropic polyurethanes containing ester mesogen units and their mesophase behavior

Abstract A series of novel thermotropic liquid crystalline was synthesized from bi(p-hydroxyl benzoic acid)hydroquinone ester (PHQ), triethylene glycol and 2,4- toluenediisocyanate (2,4-TDI) by altering the molar ratio of PHQ and diol, and PHQ was prepared by using hydroquinone and p-hydroxybenzoic acid as raw materials. The thermotropic mesophase behavior, the melting point temperature (Tm) and the isotropization temperature (Ti) of the synthesized polyurethanes were characterized by FT-IR, DSC and POM. It showed that all of the polyurethane polymers exhibited nematic textures at temperature of 110~230 °C. The shift of the melting and isotropization temperature (Tm, Ti) to lower temperature is discussed to be a consequence of the increasing amount of diol content.

Synthesis and Characterization of Hyperbranched Liquid Crystalline Polymer

Hyperbranched liquid crystalline polymer (HLCP) were prepared by pentaerythritol with 1,2,4-benzenetricarboxylic anhydride(BTCA) and p-hydroxy benzoic acid. The thermotropic properties, the melting point (Tm) and the isotropization temperature (Ti) of the synthesized HLCP were characterized by differential scanning calorimetry (DSC), fourier transform infrared spectroscopy (FTIR) and polarizing optical microscopy (POM). It showed that the new reactive thermotropic liquid polymer containing polyester mesogenic units exhibited thermotropic liquid crystalline properties between 140°C and 230°C.