Structural characteristics of
Structurally, polyorganosiloxane has the following characteristics:
(1) The main chain Si -- O -- Si bond is inorganic structure, the side chain is organic group, so it is a kind of typical semi - inorganic and semi - organic polymers.
(2) The bond Angle (SiOSi) of Si -- O -- Si bond is 130° ~ 145°, the bond length of Si -- O bond is 0.163nm ~ 0.164nm, and the bond energy is 367.8kJ/mol. The main chain of polysiloxane has the characteristics of large bond Angle, long bond length and high bond energy compared with the same group of carbon and oxygen compounds (COC108°, C -- O 0.142nm, bond energy 357.4kJ/mol).
(3) the C -- Si -- O bond Angle is 160° and the C -- Si bond length is 0.188nm, so the activation energy required for the rotation of the side chain methyl group around the Si -- O bond is low, only 8kJ/mol.
(4) The dipole-dipole interaction between the main si-O bond and the side si-CH3 interaction of polysiloxane makes the polysiloxane molecule exist only in a certain α helical structure with the methyl group outward and the si-O bond inward. This unique structure results in small chain-to-chain interactions, large molar volume, and low surface tension.
(5) Polysiloxanes with side groups of Si -- H bond, Si -- OR OR Si -- OH group are all reactive.