Yang Song,Yinhua Jin,Tianfu Yang,Jinhui Pang,Daming Zhang,Zhenhua Jiang,Baijun Liu
Aimed at clarifying the structure–property relationships of fluorinated high-performance polymers, two series of polyimides were synthesized via a two-step thermal imidization derived from isomeric diamine monomers. Furthermore, comparative studies on their properties including solubility, thermal properties, contact angles, refractive indices, dielectric constants and gas permeability were thoroughly performed. Some property differences of the isomers caused by the sequence changes were found.
A novel organic polymer monolithic column with reversed-phase/hydrophilic (RPLC/HILIC) bifunctional interaction mixed-mode was successfully synthesized with the monomers 4-vinylbiphenyl and vinylbenzyl trimethylammonium chloride and the cross-linker ethylene dimethacrylate by in situ copolymerization in a binary porogenic solvent consisting of cyclohexanol and dodecanol for capillary electrochromatography. The stationary phases formed by styrene-based monomers can allow powerful π–π, hydrophobic and hydrophilic interactions, which is beneficial for the chromatographic separation with high resolution and high column efficiency. One mixed-mode monolithic column can work as two individual mode columns based on the combination of binary RPLC and HILIC separation mechanisms. Vanillin substances and neutral and alkaline compounds can be separated perfectly on the monolithic column in different chromatographic modes which can be switched by changing the content of the organic modifier in the running phase. For benzene, the highest column efficiency was 3.49 × 105 plates per m (theoretical plates, N). The relative standard deviations of retention time of different test analytes for intra-day (n = 5), inter-day (n = 5), column-to-column (n = 3) and batch-to-batch (n = 3) reproducibility were all less than 5.0%. All these results demonstrate that the monolithic column with RPLC/HILIC mixed-mode has great application potential.
A series of liquid-crystalline 4-alkyloxybiphenyl-poly(γ-propyl- l -glutamate) conjugates (PPLG n -g-BPC m , n = 10, 54, 110, and 274, m = 4, 6, and 12) with end-on biphenyl mesogens and variable alkyl tails is synthesized via a facile copper-mediated alkyne–azide [2+3] 1,3-dipolar cycloaddition. 1 H NMR and FTIR analyses reveal a quantitative conjugation efficiency for each sample. Variable-temperature FTIR results indicate an irreversible α-helical to β-sheet transition of the PPLG 10 -g-BPC 6 in the solid state, whereas PPLG n -g-BPC m samples with a longer main-chain length ( n ≥ 54) only adopt an α-helical conformation in the temperature range between 25 and 200 °C. DSC, polarized optical microscopy (POM), and wide-angle X-ray scattering (WAXS) results collectively reveal that the PPLG n -g-BPC m samples undergo a reversible crystalline to liquid-crystalline phase transition depending on the main-/side-chain lengths. The PPLG n -g-BPC m ( n ≥ 54, m ≤ 6) samples form highly stable smectic (SmC or SmE) phases with a calculated tilt angle of 73–90°.
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