Research On Grafting Of Hyperbranched Polymer Onto Ultrafine Silica Surface

Ultrafine silica can be widely used in a series of matrix materials dueto the excellent surface adding properties and mechanicalperformances. Directly added into the organic materials, ultrafine silicacan hardly play its role due to its reunion in the reaction of active siliconsurface hydroxyl which makes the ultrafine silica hardly dispersed in thematerial showing hydrophilic oleophobic characteristics.Hyperbranched polymer surface modification is one of the popularstudies in the polymer science field nowadays. Due to its unique highlybranched molecular structure, low chain-entanglement properties, excellentdispersity and low viscosity characteristics, it can be used to improve thecompatibility with other materials.Different methods were adopted to modify ultrafine silica in this article,hyperbranched polyester modified silica and hyperbranched polyamidemodified silica were got. Grafting rate, hydrophilic property and otherproperties of hyperbranched polyester modified ultrafine silica were gotthrough particle size analysis, FT-IR characterization, TG analysis andviscosity analysis. Ester content and amino content on hyperbranchedpolyamide modified silica were characterized by saponification value analysisand amino titration. It was proved in this article that the amino content onhyperbranched polyamide modified silica grew with the growth of graftinggeneration.Epoxy resin was toughened by hyperbranched polyamide modifiedultrafine silica. Various modification of silica toughening epoxy resin coatingswere cured in this article. The effects of different grafting methods onultrafine silica toughening epoxy resin were analyzed through filmappearance analysis, film pencil hardness analysis, film flexibility analysis and film cut test. Conclusions were got as follows:（1） The particle size of hyperbranched polyester modified silica（HB-PET-SiO₂） grew as the dosage of di-methylol propinic acid （DMPA）increased, the dispersion of hyperbranched polyester modified silica changedbetter as the dosage of DMPA increased. The utmost grafting rate ofhyperbranched polyester modified silica （HB-PET-G3-SiO₂） was85.55%,when the mass ratio of KH-550modified ultrafine silica and DMPA was1:3,the content of p-toluenesulfonic acid was0.3%⁰.5%amount of DMPA, thereaction time was2h under150℃, charging the material in batches. Theproduct showed the best lipophilic and made liquid paraffin viscositychanging least.（2）The particle size of hyperbranched polyamide modified ultrafinesilica（HB-PA-SiO₂）, yet in a low extent, increased with the growth of graftinggeneration. The large branching degree of hyperbranched polyamide madelarge steric hindrance on the ultrafine silica, which limited the process ofbranching reaction. The saponification value of half generation product（HB-PA-G0.5-SiO₂） was40.7724, the content of ester on half generationgrafted ultrafine silica （HB-PA-G0.5-SiO₂） was2.8929×10^-3mol/g. With thegrowth of grafting generation, the amino content increased from7.9mmol/g ofthe unmodified ultrafine silica, to10.2mmol/g of one generation product（HB-PA-G1-SiO₂） and12.2mmol/g of two generations product（HB-PA-G2-SiO₂）. The amino content increased with the branching degreeand grafting generations. The dispersion uniformity became worse with thegrowing steric hindrance; the actual measured amino content was far less thanthe theoretical amount.（3） Hyperbranched polyester modified ultrafine silica （HB-PET-SiO₂）toughening epoxy resin was got in the condition that,3%mass ratio of epoxyresin E-44, ethanol as dilution solvent, ethylenediamine as curing agent,curing on films under170℃. The performances of cured epoxy resin were characterized, and the results showed that: the appearance of the filmschanged from colorless, clear and transparent to pale yellow, from reunion inthe edge of the film to uniformly disperse in the film as the dosage of DMPAincreased. The addition of silica didn’t affect the paint film adhesion. Filmpencil rigidity increased with DMPA dosage. The film flexibility changedbetter as the dosage of DMPA increased, and the4g DMPA modified silicashowed the best flexibility.