The Surface Modification Of Silica And Synthesis Of MQ Resin

Nano SiO2 and MQ resin are widely used fillers composing of silicon element. Nano SiO2 is nanoscale inorganic silicon oxide. MQ resin is a kind of silicone resins with special structure. Both of them have various applications in polymer composites, especially in organic liquid silicone rubber area. The dispersion and compatibility properties in liquid silicone rubber are mainly affected by the structures of two fillers. In this study, nano SiO2 aqueous (silicon sol) dispersion was modified and three kinds of MQ resins were synthesized by TEOS hydrolysis method. The relationship between the strutures of the two fillers and the processing conditions were investigated to explore their application in organic silicone materials.In the first part, hydrophilic silicon sol was modified. Nano SiO2 in silica sol was transferred to isopropanol medium by azeotropic distillation. Then the nano SiO2 was treated by several common silicone coupling agents (vinyltriethoxsilane, methyltriethoxy--silane, octyltriethoxysilane) and two self-prepared silicone coupling agents with partial similar structures of hydrogen silicone oil. The two self-prepared silicone coupling agents A and B were synthesized by hydrosilylation reactions of vinyltriethoxysilane with hydrogen silcone oil and heptamethylsiloxane separately. The structures of the products were analyzed by Infrared spectroscopy (IR). The purity of silane coupling agent B was analysized by Gas chromatography. The purity of B was about 90%. The changes of the surface hydroxyl number of nano SiO2 in isopropanol were studied after nano SiO2 modified by several coupling agents. The surface hydroxyl number of nano SiO2 was decreased with the increase of coupling agent addition.The dispersion of nano SiO2 in hydrogen silicone oil was also studied. The size of nano SiO2 modified by coupling agent B was the smallest (about 90nm). This indicated that the coupling agent with partial similar stuctures of silicone oil was beneficial for nano SiO2 to improve their dispersing behaviour in hydrogen silicone oil. In the second part, three kinds of MQ resin were synthesized by hydrolysis reaction of tetramethyldisiloxane,1,3-divinyltetramethyldisiloxane, and triethoxyphenylsilane with TEOS respectively. They were named as hydrogen-MQ resin, vinyl-MQ resin and phenyl-MQ resin. The structure of MQ resin was analysised by Infrared spectrometry (IR) and 29Si-NMR. The effects of reaction conditions on the MQ resin structures were investigated. Based on GPC analysis, the molecular compositon of the MQ resins was not uniform since multiple peaks were existed in GPC curves. The peak of lower molecular weight was oligomers resulted from the incomplete hydrolysis of TEOS with sealers. When tetramethyldisiloxane was choosed to be sealer, the proportion of oligomer to molecular weight distribution was the biggest. When triethoxyphenylsilane was choosed to be sealer, the proportion of the oligomer in the molecular weight distribution was the smallest. It was found that the molecular weight of MQ resins was decreased with the increase of M/Q. The addition sequence of reactants was also found to have great influence on the MW of MQ resin. When the sealer was added firstly and then TEOS was added after a certain time, the liquid MQ products were obtained with high viscosity and the MW was about 2000. When TEOS was added to conduct hydrolysis reaction for a certain time before the sealer was added, the solid powder MQ products were obtained with high viscosity and the MW was about 5000. The problems relating to the control of molecular weight distributions of MQ resin and reduction of oligomer are needed to be further studyied.The dispersion behavior of the three synthesized MQ resins and several kinds of commercial MQ resins in the isopropanol and hydrogen silicone oil were studied. The particles sizes of the three synthesized MQ resins were increased with their molecular weight both in the isopropanol and hydrogen silicone oil. The dispersion of the sticky liquid sample of hydrogen MQ resin was the best both in the isopropanol and hydrogen silicone oil. The particles sizes of several kinds of commercial MQ resins both in the isopropanol and hydrogen silicone oil were also found to be increased with their molecular weight.