Synthesis And Phase Behavior Of Amphiphilic Fluorinated Polyether-based Block Copolymers

Owning to the advantages of non-flammability, non-toxity, and easily accessible critical condition (Tc=31.1℃, Pc=73.8bar), supercritical carbon dioxide (scCO2) has been accepted as the most promising alternative of organic solvents, and widely used in the fields of chemistry and chemical engineering processes. While in fact, scCO2is a poor solvent for most highly polar/high molecular weight materials due to its non-polarity and low dielectric constant. Thus, additives as co-solvent or surfactant have been introduced to scCO2system so as to increase the solvability of scCO2and broaden its application. Therefore, much attention has been paid to the study involved seeking the proper surfactants used in scCO2system. The surfactant is usually amphiphilic molecule containing a CO2-philic group/fragment, and can be classified as the types of hydrophilic/CO2-philic and lipophilic/CO2-philic. So far, the fluorine-containing (poly) ether may be the most effective CO2-philic fragment.Herein, hexafluoropropylene oxide (HFPO) was used to prepare oligo-HFPO (PHFPO-CFO) via the anionic ring-opening polymerization. The acyl fluoride end group of oligo-PHFPO was esterified with the terminal hydroxyl group of polyethylene oxide (PEO) or polypropylene oxide (PPO), so as to obtain a series of amphiphilic fluorinated polyether block copolymer/oligomer with different molecular weight. The phase behaviors as well as the self-assembly of the prepared amphiphilic fluorinated polyether was also studied in both water and scCO2. The main work is summarized in three parts as follows.(1) Preparation and characterization of the fluorine-containing amphiphilic polyether. PHFPO-CFO, as well as PEO/PPO with different molecular weights was prepared via the anionic ring-opening polymerization of the relate monomers of HFPO, EO and PO, respectively. Then a series of the fluorine-containing amphiphilic polyether(s) with different molecular weights were synthesized via the esterification between the terminal hydroxyl group in PEO/PPO and the end group of-CFO in PHFPO-CFO. The prepared fluorinated polyether block copolymer(s)/oligomer(s) were characterized and verified by FT-IR, nuclear magnetic resonance spectrum (1H NMR,13C NMR,19F NMR), and ultraviolet(UV) spectrum.(2) Investigation of the phase behaviors and self-assembly of the fluorine-containing amphiphilic polyether in water. The critical micelle concentration (CMC) of every prepared polyether copolymer was measured by using the wilhelmy plate method. The polyether was dissolved in THF. And the obtained solution was then induced by dropping water so as to breed micelles. The size and the morphology of the aggregation/micelle, formed from the amphiphilic polyether solutions with the same concentration while under different molecular weights, were characterized via laser scattering and TEM, respectively. The critical surface tension was found to increase with the increase of the molecular weight (or the decrease of the fluorine content) of the amphiphilic polyether, so did the size of the corresponding micelle size.(3) Investigation of the phase behaviors of the fluorine-containing amphiphilic polyethers in scCO2. The salvation/dispersion behaviors of the amphiphilic polyethers in scCO2were investigated via the high pressure in-situ ATR-FTIR spectrum monitoring system at60.0℃. The relevance between the evolution of the intermolecular interactions and the obtained in-situ FTIR spectra in scCO2system were preliminarily disclosed, benefiting the further investigation and application of similar polyethers in scCO2system. The micro-aggregation behaviors of the amphiphilic polyethers in scCO2were investigated via the high pressure in-situ UV/VIS spectrum monitoring system, and the CMC of the polyethers in scCO2at60.0℃were also measured. For example, the CMC of PHFPO-CO-OCH2CH2OCH3in the above-mentioned conditions was obtained as approximately29.34mg.mL-1.This thesis is expected to gather experiences for the further investigation and application of the fluorinated surfactants in scCO2system. It will also provide theoretical basis for the further exploration of the micro-aggregation behaviors of the similar amphiphilic polyethers in scCO2.