Browsing by Author "Li, Chenghong"

Now showing 1 - 4 of 4
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    Amine compounds and curable compositions derived therefrom
    (United States Patent and Trademark Office, 2003-01-14)
    Disclosed are compounds produced by a process comprising the step of reacting an amine reactant with an epoxide reactant to form a hydrolytically stable carbon-nitrogen bond therebetween, wherein at least one of the amine or epoxide reactants comprises a terminal alkoxysiyl group. Also disclosed are curable compositions comprising the compounds of the present invention and the cured products derived therefrom.
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    Amine compounds and curable compositions derived therefrom
    (United States Patent and Trademark Office, 2006-11-07)
    Disclosed are compounds produced by a process comprising the step of reacting an amine reactant with an epoxide reactant to form a hydrolytically stable carbon-nitrogen bond therebetween, wherein at least one of the amine or epoxide reactants comprises a terminal alkoxysiyl group. Also disclosed are curable compositions comprising the compounds of the present invention and the cured products derived therefrom.
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    Inorganic-Organic Sol-Gel Derived Hybrid Materials as Abrasion Resistant Coatings
    Li, Chenghong (Virginia Tech, 1999-07-19)
    Inorganic-organic hybrid materials have been developed using sol-gel reactions of a trialkoxysilylated organic compound and a metal or semi-metal alkoxide and applied as coatings on polymeric or metallic substrates. Many of these coatings have demonstrated good to excellent abrasion resistance. Abrasion resistant coatings were prepared by hydrolysis and condensation of mixtures of a triethoxysilylated diethylenetriamine (f-DETA), tetramethoxysilane (TMOS), water and an alcohol in the presence of an acid catalyst (a one-step hydrolysis approach). The influences of many formulation and processing variables on the gelation time, optical properties, hardness and abrasion resistance were investigated. An aminolysis mechanism was also proposed to explain the adhesion between sol-gel derived coatings and polycarbonate substrates promoted by a 3-aminopropyltriethoxysilane (3-APS) primer. FT-IR, GPC, 1H and 13C NMR, XPS experiments were conducted to support this mechanism. The f-DETA/TMOS system is essentially a binary system of an alkyltriethoxysilane (T) and a tetraalkoxysilane (Q). At pH 0-2 and pH 4-5, the relative condensation reactivities of the T and Q species in this system were compared using 29Si NMR spectroscopy. After thermal curing, 13C or 29Si solid state NMR spectroscopy was used to estimate the extent of hydrolysis of the urea linkages in f-DETA, the concentration of residual alkoxysilane groups, and the extent of condensation for both T and Q species. The dependence of the morphology of f-DETA/TMOS gels on the pH and the water concentration was also investigated using AFM, SEM and SAXS. Many other trialkoxysilylated organic compounds containing urea, urethane, epoxy and siloxane linkages were also synthesized and utilized to prepare abrasion resistant coatings via a one-step hydrolysis approach, a two-step hydrolysis approach or a moisture-curing approach. Coatings derived from many of these systems or approaches demonstrated abrasion resistance comparable to that of the f-DETA/TMOS coating. Thin coatings were also derived from cubic octasilicate monomers via hydrosilylation or sol-gel reactions. These coatings were very transparent but unfortunately lacked abrasion resistance.
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    Preparation of Nitrile Containing Siloxane Triblock COpolymers and Their APplication As Stabilizers For Siloxane Magnetic Fluids
    Li, Chenghong (Virginia Tech, 1996-12-11)
    Nitrile containing siloxane block copolymers were developed as stabilizers for siloxane magnetic fluids. The siloxane magnetic fluids have been recently proposed as internal tamponades for retinal detachment surgery. PDMS-b-PCPMS-b-PDMSs (PDMS = polydimethylsiloxane, PCPMS = poly(3-cyanopropylmethylsiloxane) were successfully prepared through kinetically controlled polymerization of hexamethylcyclotrisiloxane initiated by lithium silanolate endcapped PCPMS macroinitiators. The macroinitiators were prepared by equilibrating mixtures of 3- cyanopropylmethylcyclosiloxanes (DxCN) and dilithium diphenylsilanediolate (DLDPS). DxCNs were synthesized by hydrolysis of 3-cyanopropylmethyldichlorosilane, followed by cyclization and equilibration of the resultant hydrolysates. DLDPS was prepared by deprotonation of diphenylsilanediol with diphenylmethyllithium. It was found that mixtures of DxCN and DLDPS could be equilibrated at 100°C within 5-10 hours. By controlling the DxCN-to-DLDPS ratio, macroinitiators of different molecular weights could be obtained. The major cyclics in the macroinitiator equilibrate are tetramer (8.6 ± 0.7 wt%), pentamer (6.3 ± 0.8 wt%) and hexamer (2.1 ± 0.5 wt%). 2.5k-2.5k-2.5k, 4k-4k-4k, and 8k-8k-8k triblock copolymers were prepared and characterized. These triblock copolymers are transparent, microphase separated and highly viscous liquids. It was found that these triblock copolymers can stabilize nanometer gamma-Fe₂O₃ and cobalt particles in octamethylcyclotetrasiloxane or hexane. Hence PDMS-b-PCPMS -b-PDMSs represent a class of promising steric stabilizers for silicone magnetic fluids.