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

Nov 22, 2019

Polymer structure characteristics, properties and applications of silicone resin


The silicone resin is a semi-inorganic semi-organic type polymer having -Si-O as a main chain and an organic group in a side chain. The silicone resin is a bulk polymer having a plurality of reactive groups, and the reactive groups are further cross-linked, that is, converted into insoluble and infusible three-dimensional structure cured products.


Silicone resin has excellent performances such as high and low temperature resistance, weathering resistance, moisture resistance, high dielectric strength, low dielectric loss, arc resistance and radiation resistance.


General purpose solution silicone resins are mainly used as base polymers for heat resistant coatings, weathering coatings and high temperature resistant electrical insulating materials.


1.2 Technological Evolution of Silicone Resins


Among all kinds of silicone polymers, silicone resin is one of the earliest synthetic and applied silicone products. Compared with the rapid development of silicone rubber pattern refurbishment technology, the technological improvement of silicone resin is relatively slow, and major technological breakthroughs are less. . Beginning about twenty years ago, due to technological advances in aromatic heterocyclic high temperature resistant polymers, some of the applications that originally belonged to silicones were squeezed, but the solvent toxicity and harsh curing conditions of aromatic heterocyclic heat-resistant polymers Limiting the application of expansion, in recent years, people have begun to pay attention to the research and development of silicone resin. Silicone resin has outstanding advantages such as wide temperature range, aging resistance and hydrophobic moisture resistance. There are indications that silicone resin may have a larger future. Development space. .


2. General purpose silicone resin


2.1 General-purpose silicone resin production process


Different types of silicone resins have different raw materials and synthetic routes. Here, only a few types of silicones are briefly introduced to their production processes.


2.1.1 methyl silicone resin


2.2.1.1 Synthesis of methyl silicone resin from methyl chlorosilane


The methyl silicone resin is synthesized by using methylchlorosilane as a main raw material. Since the structure and composition of the silicone resin are different (the degree of crosslinking of the silicone resin, that is, the [CH3]/[Si] value), different synthesis conditions are required.


When the low R/Si([CH3]/[Si]≈1.0) methyl silicone resin is synthesized, the hydrolysis and condensation reaction rate of the main raw material monomer methyltrichlorosilane is quite fast, and the reaction temperature must be strictly controlled to not exceed 0 °C. It is also necessary to carry out the reaction in a complex solvent, and the reaction product is stored for only several days at room temperature. The practical value of such products is not great.


Methyl chlorosilane is used to synthesize methyl silicone resin with larger R/Si. Although the hydrolysis condensation reaction of methyltrichlorosilane and dimethyldichlorosilane is slightly slower than the hydrolysis condensation reaction with methyltrichlorosilane. However, the hydrolytic condensation reaction speed difference between methyltrichlorosilane and dimethyldichlorosilane is too large, and the mixed hydrolyzate and the raw material monomer do not match each other because of the premature hydrolysis and condensation of methyltrichlorosilane. And methyl trichlorosilane is often subjected to advanced hydrolysis condensation to form a partially crosslinked gel, and the resulting methyl silicone resin has poor overall performance.


2.2.1.2 Synthesis of methyl silicone resin from methyl alkoxysilane


The hydrolysis condensation reaction rate of the methyl alkoxysilane can be controlled by changing the reaction conditions, and a methyl silicone resin having a different degree of crosslinking can be synthesized from the methyl alkoxysilane.


The commercial methyl silicone resin with medium cross-linking degree ([CH3]/[Si]≈1.2-1.5) is mostly obtained by hydrolysis condensation reaction of methyl alkoxysilane: methyl triethoxy group refined by acid removal. Mix silane and dimethyldiethoxysilane monomer with water, add trace amount of hydrochloric acid or appropriate amount of strong acid type cation exchange resin (large pore strong acid type ion exchange resin has better catalytic effect), activated clay (drying after acidification) As a catalyst, heating, and carrying out a hydrolysis reaction, when the end point is reached, an appropriate amount of hexamethyldisilazane is added to neutralize the catalyst hydrochloric acid, or an ion exchange resin or activated clay as a catalyst is filtered to terminate the condensation reaction. The product obtained was an alcohol solution of methyl silicone resin.


2.2.2 Methyl phenyl silicone resin


The main raw materials for industrial production of methyl phenyl silicone resin are methyltrichlorosilane, dimethyldichlorosilane, phenyltrichlorosilane, diphenyldichlorosilane, and some or all of the above monomers are doped with toluene or xylene. After mixing in an appropriate ratio, dropwise adding to water under stirring, controlling the temperature to carry out a hydrolysis reaction, removing the reaction by-product HCl (aqueous hydrochloric acid solution) by water washing to obtain a hydrolyzed silanol solution, and then distilling off part of the solvent to form a concentrated silanol, and then The silicone resin is obtained by cold condensation or thermal condensation reaction, and finally filtered and packaged to obtain a finished silicone resin.


2.2.3 Universal methyl phenyl vinyl silicone resin and related components


The production process of methylphenyl vinyl silicone resin and methyl phenyl silicone resin is similar, except that in the hydrolysis raw material, in addition to methylchlorosilane and phenylchlorosilane monomer, an appropriate amount of methylvinyl dichloride is added. A vinyl-containing silicone monomer such as silane. The mixed monomer is hydrolyzed, washed with water, and concentrated to obtain a concentrated hydrolyzed silanol, added with a metal organic acid salt catalyst, heated and condensed under reduced pressure to a predetermined viscosity, or controlled by a gelation time to obtain a methylphenyl group. Vinyl silicone resin.


a methylphenyl hydrogen-containing polysiloxane used as a component of a methylphenylvinyl silicone resin addition reaction crosslinking agent, usually a cyclic or linear polymer having a small degree of polymerization, which is a methyl group. Hydrogen-containing dichlorosilane is obtained by hydrolyzing cyclization or by cohydrolysis condensation of methyl hydrogen dichlorosilane, phenyltrichlorosilane and trimethylchlorosilane.


The reactive diluent used for the addition of silicone resin is a low viscosity methyl phenyl vinyl polysiloxane. The synthesis method is similar to that of the methyl silicone vinyl silicone resin which is the main component of the addition silicone resin. The difference lies in the raw material distribution. The amount of the monomer having a vinyl side chain and the monofunctional monomer (header) is relatively large, thereby obtaining a low-viscosity polymer having a high crosslinking activity.


2.2.4 Modified silicone resin


The production of the organic resin blend-modified silicone resin is usually carried out by adding an organic resin such as an alkyd resin, a phenol resin or an acrylic resin to a toluene or xylene solution of methylphenyl silicone resin, and uniformly mixing to obtain a finished product.


Copolymer modified silicone resins are produced by a series of chemical reaction processes. The organic resins copolymerizable with the silicone resin are polyester, epoxy, phenolic, melamine formaldehyde, polyacrylate, and the like. A variety of synthetic routes can be used to prepare the copolymerized silicone resin, but a more practical industrial production method is copolymerization of silanol and an organic resin. That is, the methyl chlorosilane and the phenylchlorosilane monomer are first co-hydrolyzed to obtain a hydrolyzed silanol solution or a concentrated solution, and then the previously synthesized organic resin prepolymer is added thereto, and the solvent is further mixed and evaporated. The catalyst such as zinc octoate and zinc naphthate is co-condensed at a temperature of 150-170 ° C until the reaction material reaches an appropriate viscosity or a predetermined gelation time, cooled, dissolved in a solvent, and filtered to obtain a finished copolymerized silicone resin.


RH-SP601-Transparent-Liquid-Heat-resistance-Phenyl



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