1. Silicone
Organosilicon, that is, organosilicon compounds, refers to compounds containing Si-C bonds, and at least one organic group is directly connected to silicon atoms, and it is customary to often regard those compounds that connect organic groups with silicon atoms through oxygen, sulfur, nitrogen, etc., as organosilicon compounds. Among them, polysiloxane composed of silico-oxygen bond (-Si-0-si -) as the skeleton is one of the most numerous organosilicon compounds with deep research and wide application, accounting for more than 90% of the total dosage.
Silicone materials have a unique structure:
(1) Sufficient methyl groups on Si atoms shield the high energy polysiloxane main chain;
(2)C-H is non-polar, so that the intermolecular force is very weak; (3) The Si-O bond length is long, and the SI-O-Si bond Angle is large.
(4)Si-O bond is a covalent bond with 50% ionic bond characteristics (covalent bond is directional, ionic bond is non-directional).
2. organic silicone resin
Silicone resins are highly cross-linked, reticulated polyorganosilanes, usually various mixtures of methyltrichlorosilanes, dimethyldichlorosilanes, phenyltrichlorosilanes, diphenyldichlorosilanes, or methylphenyldichlorosilanes that are decomposed with water at lower temperatures in the presence of an organic solvent such as toluene to produce acidic hydrolysates. The initial product of hydrolysis is a mixture of cyclic, linear, and cross-linked polymers, often with considerable hydroxyl groups. The hydrolysate is washed to remove the acid, and the neutral primary polycondensation is thermally oxidized in the air or further polycondensation in the presence of catalyst, and a highly cross-linked three-dimensional network structure is formed after Z.
Component structure
Curing is usually achieved by the condensation of silanol to form silicone chains. When the condensation reaction is carried out, due to the gradual reduction of silanol concentration, the steric hindrance is increased, and the fluidity is poor, resulting in a decrease in reaction rate. Therefore, to make the resin fully cured, it is necessary to heat and add a catalyst to accelerate the reaction. Many substances catalyze the condensation of silanol, including acids and bases, soluble organic salts of lead, cobalt, tin, iron and other metals, organic compounds such as dibutyltin dilaurate or N, N, N', N' tetramethylguanidine salts.
The performance of the finished product of silicone Z depends on the number of organic groups contained (that is, the ratio of R to Si). Generally, silicone resins with practical value have a ratio of R to Si in their molecular composition between 1.2 and 1.6. The general rule is that the smaller the value of R:Si, the more the silicone resin can cure at a lower temperature; The larger the value of R:Si, the obtained silicone resin to cure it needs to be baked at a high temperature of 200~250℃ for a long time, the resulting film hardness is poor, but the thermoelasticity is much better than the former.
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