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Self-healing Polymer Composites

Author: YangHaiTang
Tutor: FangZhengPing
School: Zhejiang University
Course: Polymer Chemistry and Physics
Keywords: Polymer composites self-healing hydrosilylation organosilane oligosiloxane monomer Pt-based catalyst carrier-supported catalyst
CLC: TB381
Type: PhD thesis
Year: 2007
Downloads: 605
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Abstract


A novel self-healing polymeric composite system was designed based on an overview in the latest progress of "implant" self-healing polymeric composites. Considering the unsolved problems in the research of self-healing polymeric composites and the properties of hydrosilylation reaction and its catalyst, hydrosilylation reaction was employed to fulfill the order of healing crack. Healing is accomplished by incorporating a microencapsulated healing agent dispersed in matrix and by a supported catalyst on particle or fiber fillers. The catalyst fixed on supported platinum catalyst which can catalyze hydrosilylation reaction quickly at ambient atmosphere. The healing agent could be a kind of oligo-organosiloxane which contained both Si-H bonds and Si-vinyl bonds.SiO2 supported Karstedt-type catalyst was prepared by the platinum complex with Si-vinyl bonds, which bonded on the surface of SiO2 through the coupling treated by vinyltriethoxysilane. Kinetics of hydrosilylation reaction between dimethylphenylsilane and styrene catalyzed by SiO2 supported Karstedt-type catalyst were studied. The results show that the activity energy of this hydrosilylation is 93.32 KJ/mol, which means the SiO2 supported Karstedt-type catalyst was a high activity catalyst for hydrosilylation of dimethylphenylsilane and styrene.Methyl-(γ-chloropropyl) dichlorosilane was synthesized under the catalysis of a SiO2 supported Karstedt-type catalyst. By orthogonal experimental design method, the optimum reaction parameters such as reactants ratio, reaction temperature and time, and the dosage of catalyst, were determined. At the optimum reaction condition the product yield reached 78.42%, which is higher than that reported in the literatures.A platinum-based catalyst supported on glass fiber (GF-Pt-Ⅱ) grafted with 1,3,5,7-tetramethyl-1,3,5,7-trtravinyl cyclotetrasiloxane (D4Vi) was prepared. Silanization of glass fiber was carried out with methyldichlorosilane. D4Vi was anchored on the modified fiber through a hydrosilylation reaction with Si-H bonds, mediated by a Pt(0)-D4Vi complex solution catalyst. Fourier transforms infrared spectroscopy, field emission scanning electron microscope, x-ray energy dispersion spectroscopy and thermogravimetric analysis provided evidences that D4Vi was covalently bonded onto the surface of fiber. The activity of GF-Pt-Ⅱwas evaluated in the hydrosilylation reactions of styrene and methyldiethoxysilane (or triethylsilane). A fairly good catalytic activity to the hydrosilylation reaction between styrene and methyldiethoxysilane (or triethylsilane) was observed on GF-Pt-Ⅱ.There was no reaction between methylvinyldichlorosilane (MeViSiCl2) and hexamethyl-cyclotrisiloxane (D3) with hexane as solvent. In contrast, there were some ring-open products (where, n=3, 4, or 5) found with toluene as solvent. Moreover,(?) and (?)(n=3 or 4) were found in thesystem catalyzed by dense hydrochloric acid.Oligomer of organosiloxane containing multiply vinyl group and Si-Cl bonds was prepared through the ring-open of D4Vi ended with MeViSiCl2 under accelerating by dimethylformamide and acetonitrile. After alcoholysis of the oligomer by anhydrous ethanol, the coupling agent containing multiply vinyl group was acquired. And the healing agent (I) containing both multiply vinyl group and double Si-H bonds was prepared by reducing the oligomer by lithium aluminum tetrahydride.α,ω-dichloropolymethylvinylsiloxane was prepared by hydrolyzing partially of MeViSiCl2 under nitrogen protected in ether (as a solvent). And theα,ω-dichloropolymethylvinylsiloxane can be reduced by lithium aluminum tetrahydride, to acquire the healing agent (Ⅱ) containing both multiply vinyl group and double Si-H bonds.Polymerizations of healing agent I andⅡcatalyzed by Karstedt catalyst, SiO2-Pt and GF-Pt-Ⅱwere investigated. The results show that the healing agent can be polymerized by hydrosilylation reaction. The product of hydrosilylation occured on the urface of glass fiber as indicated by SEM micrographs and it is in favor of interface joints between the fiber and matrix.

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