Synthesis Of Fluorine-containing Epoxy Oligomer-based Ethylbenzene And Its Solvation Behavior In Supercritical CO₂

In recent years,much attention has been paid to supercritical carbon dioxide(scCO2)because of its unique advantages.ScCO2 is safe,cheap,renewable,chemical inert,and the critical point is readily accessible.More importantly,its chemical and physical properties can be continuously adjusted by altering the temperature and/or pressure,which lays a solid foundation for the intensification of mass transfer and the effective control of reaction.Moreover,scCO2 exhibits low viscosity and high diffusion coefficient,contributing to a better swelling and plasticizing on polymers.Additionally,scCO2 can be completely removed via decompression without any residual of organic solvent at the end of the reaction.Owing to such advantages,scCO2 is increasingly accepted as a green and efficient medium for the synthesis of a variety of polymers.Though most monomers exhibit good solubility in scCO2,while due to CO2 is a non-polar molecule,scCO2 has considerably poor solvability to many polar oligomers or polymers,resulting that the corresponding monomers can hardly be polymerized homogeneously in scCO2.The bigger the molecular weight of polymer becomes,the worse the homogeneity of polymerization system will be,which brings great challenges and obstacles to the synthesis of fine chemicals as well as polymeric functional materials in scCO2.So far the poor/limited solubility of polymers in scCO2 has impacted negatively on the controllability of the polymerization and the resulted structure and performance of the polymers.The structure of solute has a significant effect on its solvation behaviors and solubility in scCO2.As compared with the non-fluorinated organic compounds,most fluorinated ones exhibit much better solubility in scCO2.In our previous study,it was proved that the fluorinated epoxide oligomers(FEO)exhibited the most excellent solubility in scCO2 under relatively moderate conditions,and thus were expected to be the most efficient solubilizing chains in scCO2 system.It is of great significance to implant such solubilizing chain to design and construct novel monomers(or precursors for certain fluorinated monomers)and special co-solvents so as to realize a homogeneous polymerization in scCO2.Ethylbenzene is the most important intermediate or precursor for the preparation of styrene,and is one of the most important solvents in polymeric chemistry especially in the synthetic rubber field.In this thesis,the oligomers of hexafluoropropene oxide((HFPO)n,n=2,3,4)are intentionally selected as the solubilizing chain and introduced to ethylbenzene,via which three precursors of novel fluorinated styrene monomers,fluorinated epoxide oligomer based ethylbenzene(FEOnEB,n=2,3,4)are designed and synthesized.Such FEO,EB may also be used as the co-solvents for the polymerization of fluorinated monomers in scCO2.Further more,the solvation behaviors of FEOnEB in scCO2 are also explored.The main contents are presented as follows:(1)Preparation and characterization of FEOnEBFirst,three kinds of FEOnEB with different chain lengths or degree of polymerization(n=2,3,4)were prepared via Friedel-Crafts acylation,in which ethylbenzene and(HFPO)n are used as the reactants,anhydrous AlCl3 and other Lewis acids are employed as the catalysts.The effects of catalyst species,catalyst dosage,temperature and reaction time on the acylation were investigated and the optimized reaction conditions were obtained.Second,organometallic reagents were used to synthesize FEOnEB.The reaction conditions were also optimized.Finally,the prepared FEOnEB was characterized via 1H NMR,13C NMR,FT-IR and HRMS,via which the structure of the products was confirmed.It is shown that the needed FEOnEB was successfully synthesized.As compared with the results of Friedel-Crafts acylation,the strategy using organometallic reagents was more efficient,via which the yield of FEOnEB reached up to 81.2%.(2)Exploration of solvation behaviors of FEOnEB in scCO2The solvation behaviors of FEOnEB in gaseous and scCO2 were investigated by using a set of high-pressure in-situ FT-IR spectrum monitoring system as the temperature and pressure stepwise increased from 40.0 to 70.0 ? and 0 to 38.0 MPa respectively.Based on the vibrational absorption evolution of the functional groups,the intermolecular interaction in FEOnEB+CO2 binary system was investigated.It is shown that FEOnEB can be sufficiently dispersed and dissolved in scCO2 under a relatively lower pressure at 40.0 to 70.0 ?,and may be miscible with scCO2 under mild temperature and pressure.The maximum transition pressure(PT)of FEOnEB+CO2 system is only 13.0 MPa(at 70.0 ?).That is to say,the synthesized FEOnEB exhibits excellent solubility in scCO2,and thus is a promising precursor of fluorinated monomers and effective co-solvents for scCO2 polymerization system.Meanwhile,the result verified that the introduced(HFPO)n could greatly improve the solubility of FEOnEB in scCO2,and even may be the most efficient solubilizing chain for scCO2 system.The synthesized FEOnEB proves the rationality of the hypothesis of intermolecular-interaction dynamically induced solvation effect(IDISE)that we proposed recently,and fully verifies the efficiency of the solubilizing chain of(HFPO)n,which lays a solid foundation for exploring and constructing the controllable polymerization system in scCO2.