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Polymer structure characteristics, properties and applications of silicone resin part II

Nov 25, 2019

3. High performance silicone resin


The general-purpose silicone resin prepared according to the aforementioned mature process and formulation can meet most of the conventional use requirements, but due to some inherent defects of the existing old type silicone resin, it cannot fully meet the higher use requirements. In order to meet the demanding requirements of higher performance, there is an urgent need to improve the synthesis process and formulation of the old products, and to develop new silicone resins with higher performance according to the needs of the development of new technologies.


3.1 high curing active methyl phenyl silicone resin


Methyl phenyl silicone resin is the largest and most widely used type of silicone resin. The existing models of methyl phenyl silicone resin in China and abroad generally have the disadvantages of low curing activity, weak adhesion of the coated film to the substrate after curing, and easy returning of the coating film after curing. These stubborn defects greatly limit the application of silicone.


The general-purpose methylphenyl silicone resin generally uses methylchlorosilane and phenylchlorosilane as main raw materials, and is obtained by co-hydrolysis-water washing-concentration-thermal condensation and the like to obtain a silicone resin. Hydrolysis of organochlorosilane releases HCl, and then HCl dissolves in water to form a strong acidic medium. Under acidic conditions, the hydrolysis of organochlorosilane, in addition to mainly producing silanol polymer, also produces cyclic or cage inert silicone. polymer. In the subsequent thermal condensation reaction process, most of the highly reactive groups in the silanol are consumed, and the obtained silicone resin has low curing activity, and the cured coating film has weak adhesion to the substrate. The organochlorosilane monomer is hydrolyzed in an acidic medium, and the resulting cyclic or cage-type inert silicone polymer remains in the silicone polymer, which is equivalent to the latent solvent of the silicone resin. After the silicone resin film is cured, it is inert. The migration and swelling of the silicon ring type or cage type oligomer causes the silicone resin film to be back-sticked.


In order to overcome the above defects of methyl phenyl silicone resin, the author improved the synthesis process, the main key technologies are: 1 to adjust the conditions of silanol condensation reaction, to achieve sufficient high activity reactive groups in the silicone resin to improve the silicone resin Curing reaction activity and improving bonding performance; 2 eliminating inert ring-type or cage-type silicone oligomer remaining in the silicone resin, improving the yield of the silicone resin synthesis reaction and eliminating the stubborn disadvantage of easy back-sticking of the silicone resin after curing.


The special catalyst is used to catalyze the condensation reaction of methylphenyl silicone resin. The selective catalytic property of the nucleophilic reaction makes the phenyl substitution position in the molecular chain of methylphenyl silanol preferentially activated, thereby initiating the silanol group at the phenyl substitution position. The condensation reaction is carried out prior to the silanol group at the methyl substitution position to form a polymer chain of the methylphenyl silicone resin, so that a part of the methyl group at the methyl substitution position remains in the polymer. During the curing reaction of the silicone resin, the reactivity of the methyl-substituted silicon hydroxy group is significantly higher than that of the phenyl group corresponding to the phenyl group, thereby obtaining a highly reactive methylphenyl silicone resin. The large proportion of low sterically hindered, highly reactive methyl substituted silanol groups retained in the silicone polymer enhances the adhesion of such silicone cured materials to substrates.


Another function of the effect catalyst is to catalyze the ring opening reaction of the polycondensation process. The inert silicone macrocycles and cage polymers formed during the hydrolysis of organochlorosilanes also undergo open-loop participation in polycondensation under the action of special catalysts, eliminating inert large rings and cage polymers, thus completely solving the problem. The thermal condensation silicone resin is easy to return to the basic defects after curing; at the same time, the special effect catalyst promotes the inert ring type or cage oligomer to participate in the polymerization reaction, and also helps to precisely adjust the composition ratio of the silicone resin and improve the product yield.


The above selective catalyst has strong catalytic activity, the catalytic condensation reaction rate is fast, the curing reaction of the silicone resin obtained by the condensation reaction is high, and the synthesis reaction is ensured smoothly, and the curing activity and storage stability of the silicone resin are required to be considered, and the high curing activity is required. The production of silicone resin requires a condensation reaction at a relatively low heating temperature, and an effective monitoring means for controlling the progress of the condensation reaction must be provided. To this end, three methods for monitoring the end point of the condensation reaction of the silicone resin and evaluating the properties of the silicone resin were determined: 1 to determine the degree of condensation reaction by measuring the amount of water removed during the progress of the silanol condensation reaction; 2 by measuring the relative viscosity change of the material during the reaction. To determine the molecular weight growth of the polymer; 3 to determine the curing performance of the silicone resin by measuring the gelation time of the material.


The above improved process is applied to save energy and improve product yield. The obtained methyl phenyl silicone resin completely overcomes the excellent curing performance, low adhesion and curing of methyl phenyl silicone resin, in addition to the excellent properties of high temperature resistance, weathering resistance and high dielectric strength of the silicone resin. After the easy back to the sticky serious shortcomings. The high-curing reactive silicone resin synthesized by the nucleophilic reaction can not only crosslink and cure at a lower temperature, but also the silicone cured film adheres firmly to a plurality of substrates, and the cured coating film never returns to the viscosity, and the actual test is performed. The penetration strength reached 116 MV/m, the breakdown strength was still as high as 99 MV/m after 24 hours of moisture, and the high breakdown strength of 59 MV/m was maintained at 200 °C. The high curing reactive methyl phenyl silicone resin has excellent adhesion properties. I have used high-curing reactive silicone resin to coat single-crystal silicon test pieces. After the silicone resin is cured, it is firmly bonded to the single-crystal silicon test piece, and then the single-crystal silicon test piece coated with the silicone resin film is subjected to a thermal shock test: After heating in an oven at 150 ° C for 30 minutes, and then taking out the frozen brine which was immediately put into -40 ° C, the thermal shock was repeated 5 times, and 4 of the 5 test pieces were stably bonded to the single crystal silicon, and the other was Although the silicone film layer of one test piece is peeled off, the peeling interface is inside the single crystal silicon layer, and a thin layer of single crystal silicon is adhered to the peeled silicone resin layer, which shows that the bonding strength is large. .


RH-SH-3B-Transparent-Liquid-High-Reactive




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