| Fluoropolymers have attracted great attention in the field of piezoelectric materials,dielectric materials,ionic conduction membranes and so on.The chemical structure of the fluoropolymers plays a crucial role in the performance and application of the fluoropolymer materials.Generally,the functionalization of fluoropolymer was carried out by copolymerization but the process is quite limited.Besides,due to the strong electronegativity of the fluorine atom,the C-F bond has a higher bond energy which is difficult to open via conventional chemical methods.In our previous research,it was found that the imidazolium-type ionic liquids have strong dipolar interaction with poly(vinylidene fluoride)(PVDF)which led to the homogenous dispersion of the ionic liquid molecules in the amorphous region of the PVDF matrix.The ionic liquids attached with vinyl groups can be successfully grafted onto the PVDF chains under the electron beam(EB)irradiation.However,the molecular structure of PVDF is regular and the crystallinity is always higher than 50 %,which limits the adding of ionic liquids into the PVDF matrix.The ionic liquids over-feeded can be easily excluded from the PVDF matrix,and only low degree of grafting can be achieved which restricted the application of the functionalized PVDF.In this dissertation,poly(vinylidene fluoride-co-hexafluoropropylene)(P(VDF-co-HFP))was chosen in order to increase the degree of grafting of ionic liquids.Compared with VDF unit,the HFP unit with larger steric hindrance can effectively hinder the regular arrangement of VDF segment and decrease the crystallinity which endow the macromolecular chains better flexibility.Meanwhile,more C-F bonds were introduced in the copolymer which enhanced the compatibility between ionic liquids and polymer chains.It is worth noticed that the change of the macromolecular structure can result in the difference in the interaction and spatial relationship between ionic liquids and P(VDF-co-HFP)comparing with PVDF/ionic liquids blends.Here,it is first investigated the dipolar interactions between P(VDF-co-HFP)and imidazolium-type ionic liquids with different anions and the dispersion of ionic liquids into the fluoropolymer matrix.By EB irradiation,the "fixed" and "block" grafting modification of fluoropolymers were achieved in the P(VDF-co-HFP)/ionic liquids blends.In addition,the modified fluoropolymers were applied in the field of polymer gel electrolytes and antibacterial materials and a series of innovative research results have been achieved.The main results of this dissertation are listed as follows:(1)Study on the regulation of microstructure and the "fixed" grafting modification in the P(VDF-co-HFP)/ionic liquids blends.It is investigated the dipolar interactions between P(VDF-co-HFP)and imidazolium-type ionic liquids with different anions and the dispersion of ionic liquids into the fluoropolymer matrix.The results indicated that the the ionic liquid,1-vinyl-3-butylimidazolium bis(trifluoromethylsulfonyl)imide(IL-TFSI),which have stronger dipolar interactions with HFP segments than the VDF segment,can selectively interact with HFP segments and formed the nanodomains in the matrix.For the similar dipolar interactions of 1-vinyl-3-butylimidazolium chloride(IL-Cl)with VDF and HFP segments,ionic liquids,IL-Cl,were homogenously dispersed in the matrix.When the polymer/ionic liquids blends were irradiated under EB,the ionic liquids can be in-situ grafted onto the fluoropolymer chains,and the IL-TFSI can be "fixed" grafted onto the HFP-segments for the selective distribution in the HFP-rich regions.The study provides a simple and effective strategy to realize the selective modification of the fluoropolymer.(2)Preparation of quasi "block" graft copolymers via semicrystalline polymer binary-phase structure template and regulation of microstructures.The quasi "block" ionic liquid-grafted copolymers have been prepared through combining the semicrystalline polymer binary-phase structure template and EB irradiation.Meanwhile,the microstructure of the quasi "block" grafted copolymers can be easily regulated by changing the ionic liquids grafting ratios.The quasi "block" grafted copolymer exhibited excellent mechanical properties and low resistivity which may have potential application in the field of energy conversion devices and flexible electronic devices.The study provides a possible method to produce functional polymers massively in the future.(3)Preparation of crosslinked polymer gel electrolytes and investigation of electrochemical performance.The crosslinked polymer gel electrolytes have been successfully prepared through EB irradiation.With the strong dipolar interaction between imidazolium-type ionic liquids and fluoropolymer chains,mass of ionic liquids can be absorbed into the crosslinked P(VDF-co-HFP)/triallyl isocyanurate(TAIC)films and fomed the crosslinked fluoropolymer gel electrolytes.The crosslinked fluoropolymer gel electrolytes exhibited excellent thermalstability and mechanical performance.In the tensile test,the crosslinked electrolytes show higher tensile strength of 10.6 MPa,while the uncrosslinked electrolytes is only 0.4 MPa.The electrochemical test indicated that the crosslinked fluoropolymer gel electrolytes own good ionic conductivity and electrochemical stability which may have potential application in the polymer lithium-ion batteries and flexible devices.(4)Preparation of durable anti-superbug fluoropolymers and investigation of the performance.With EB irradiation induced grafting,the antibacterial agent(ionic liquid)was successfully grafted onto the PVDF chains.The modified fluoropolymers still maintained the original mechanical properties of the neat PVDF and can be also reprocessed.The ionic liquid-grafted PVDF exhibited good mechanical properties and thermalstability.In addition,for the enrichment of ionic liquids graft chains on the surface of materials,the nonwovens and membranes of modified polymers showed excellent broad-spectrum antibacterial properties.By virtue of the chemical bonds between ionic liquids and PVDF chains,the modified polymer materials also exhibited durable antibacterial performance which may have potential application in the field of life,medical care and other aspects. |
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