Preparation And Properties Of Poly(L-glutamate) Derivatives Bearing N-Butyl Imidazolium Bromide

Polymer ionic liquids are a type of polyelectrolytes containing ionic liquid species in the main chain or the side chain. They have good thermal stability, chemical stability, high conductivity, and other properties(e.g., dispersibility of carbon nanotubes). Polypeptides are a kind of materials consisting of natural amino acids and their derivatives by amide bonds. They are able to form stable secondary structures(e.g., α-helices and β-sheets) under certain conditions. Their secondary structures play an important role in molecular rigidity and liquid crystalline self-assembly behaviors.Therefore, the incorporation of ionic liquid moieties in the side chains of polypeptides may lead to new poly(ionic liquids) with highly ordered molecular structures.In this dissertation, we designed and synthesized a series of poly(L-glutamate)derivatives bearing N-butyl imidazolium bromide(PPLG-g-BIB) with different number average molecular weights, investigated their bulk properties, and explored their potential application for dispersing single walled carbon nanotube(SWCNT) in water. Additionally, we prepared a series of poly(L-glutamate) derivatives bearing Nbutyl imidazolium bromide and p-tolyl groups(PPLG-g-BIB/MPB). The polymers showed good solubility in polar organic solvents. When the ratio of imidazolium and p-tolyl groups was 46:54, the polymer exhibited ordered liquid crystalline phase with hexagonal packing. Details are as follows:1. A series of PPLG-g-BIB with different number average molecular weights were synthesized by ring-opening polymerization and copper-mediated [2+3] alkyne-azide1,3-dipolar cycloaddition(i.e., click chemistry). Nuclear magnetic resonance spectroscopy(NMR) and fourier transform infrared spectrometer(FTIR) confirmed the molecular structures of the polymers. The molecular weights and molecular weight distributions of the polymers were determined by gel-permeation chromatography(GPC). FTIR results showed that the polymers adopted α-helical conformation both in the solid state and solution. PPLG-g-BIB dispersed SWCNT solutions have been prepared. Ultraviolet-visible spectrophotometer(UV-VIS)revealed that the SWCNT dispersibility in water was improved by either adjusting the polymer to SWCNT weight ratios or decreasing the polypeptide main-chain length.2. A series of PPLG-g-BIB/MPB were prepared by copper-mediated [2+3] alkyneazide 1,3-dipolar cycloaddition(i.e., click chemistry). NMR and FTIR results confirmed the molecular structures. FTIR results showed that the polymers adopted α-helix in the solid state. The bulk properties of the polymers were studied by thermogravimetric analysis(TGA), differential scanning calorimetry(DSC) and polarized optical microscope(POM). The results showed that their glass transition temperature(Tg) and thermal decomposition temperature(Td) were in the range of 12-42 ℃ and 238-244 ℃, respectively. When the molar percentage of imidazolium groups was less than 46%, the polymers were able to form liquid crystalline phases.Their Tg, Td, and liquid crystal clear point temperature increased as the content of ptolyl groups increased. One-dimensional wide-angle X-ray scattering(1D WAXS)results suggested that the liquid crystalline polymers formed ordered nematic phase with hexagonal packings.