Method for Preparing Thermosetting Methylphenyl Organosilicon Resin
May 17, 2024
The most commonly used method for preparing thermosetting methylphenyl silicone resin is through co hydrolysis condensation reaction of two functional and three functional organic silicon monomers.
There are two ways in the condensation reaction process: intermolecular condensation and intramolecular condensation. Only intermolecular condensation can increase molar mass. In the manufacturing process of silicone resin, the key to controlling the molar ratio is the ratio of intermolecular and intramolecular condensation reactions, and inhibiting intramolecular cyclization reactions is an important factor.
There are four main factors that affect the molar mass fraction of silicone resin:
As the temperature of the CD reaction increases, the content of functional groups in the resin decreases, which has no effect on the cyclization reaction.
The concentration of acid increases, the concentration of light groups decreases, and the trend of cyclization increases.
An increase in solvent content has no effect on the content of functional groups, but the trend of cyclization increases, resulting in the production of low molar mass silicone resin.
Alcohol is a water-soluble solvent that has little effect on the content of tibial groups, but significantly increases the mixing of the two phases for cyclization, which is beneficial for cyclization reactions in non-aqueous phases. Therefore, the amount of alcohol added can be used as a means to control the molar mass size.
The molecular structure characteristics determine the high heat resistance of silicone resin
Silicone resin is a thermosetting resin. When subjected to thermal oxidation at high temperatures, only the organic groups in the side chains break and decompose, releasing their oxides. However, the silicon oxygen bonds in the main chain are rarely broken, ultimately resulting in the formation of a polymer in the form of - f0- Si-0, which has high thermal stability,The main reason is:
Due to the fact that the macromolecular chains of silicone resin are composed of - Si - () - Si - bonds, and the Si () - oxygen bond has a high bond energy (373k]/mol), it has excellent thermal oxidation stability and good heat resistance. Its heat resistance is much better than that of ordinary organic resins, that is, the covalent bond energy of Si-0 bond is greater than that of C-C bond in ordinary organic polymers.
However, due to the organic groups attached to silicon atoms, organic silicon has poorer thermal stability than inorganic substances such as quartz. The difference in relative electronegativity between silicon atoms and oxygen atoms in Si-0 bonds is large. Due to the high polarity of Si-0 bonds, there is a 50% ionization tendency, which has a dipole induction effect on the ligands connected to Si atoms, improving the stability of the connected light groups for oxidation. This stability is much higher than that of the same functional group on ordinary organic polymers; That is to say, the Si-0-Si chain can provide a shielding effect on the oxidation of the connected tibia groups.
In organic silicon polymers, silicon atoms and oxygen atoms form a d-p six bond, which increases the stability and bond energy of the polymer, as well as its thermal stability.
The c-c main chain of ordinary organic polymers is easily broken into low molecular structures due to thermal oxidation After being thermally oxidized, the silicon atoms connected to organic silicon polymers generate highly cross-linked and more stable Si O-Si bonds, which can prevent the breakage and degradation of their main chains.
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