Additive liquid silicone is a type of organic silicon material that is made up of polydimethylsiloxane containing vinyl groups as the base polymer, hydrogen containing silicone oil as the crosslinking agent, and vulcanized into elastomers at room temperature or by heating the crosslinking agent in the presence of platinum based catalysts. Compared to condensed liquid silicone, additive liquid silicone has advantages such as no by-products, minimal shrinkage, deep vulcanization ability, and no corrosion to materials in contact during crosslinking and vulcanization. In recent years, additive liquid silicone has become the fastest-growing variety among various types of silicone.
In recent years, the improvement of mechanical properties and application development of additive liquid silicone have received widespread attention. There have been numerous reports on the effect of white carbon black on the properties of additive liquid silicone. Hydrogen containing silicone oil also has a significant impact on the mechanical properties of addition molded liquid silicone; Currently, there is relatively little research in this area.
A liquid adhesive was prepared using multi hydrogen containing silicone oil with the same viscosity but different active hydrogen mass fractions as a crosslinking agent, and vulcanized test pieces were made to determine its mechanical properties. When the mass fraction of active hydrogen in hydrogen containing silicone oil increases from 0.43% to 1.57%, the tensile strength of the liquid adhesive increases from 4.7 MPa to 6.1 MPa, the Shore A hardness gradually increases, and the elongation at break decreases from 490% to 255%. This is because the viscosity of hydrogen containing silicone oil remains unchanged, and as the mass fraction of active hydrogen increases, the molecular chain segments between actual crosslinking points become shorter, resulting in a decrease in the strength, hardness, and elongation of the liquid adhesive; When the mass fraction of active hydrogen in hydrogen containing silicone oil increases from 0.75% to 1.57%, the change in tear strength is not significant. This can be explained as: when the mass fraction of active hydrogen in hydrogen containing silicone oil increases to 0.75%, the Si-H bonds in the crosslinking agent molecular chain are relatively concentrated, resulting in a steric hindrance effect that makes the effective crosslinking point of the liquid adhesive increase less significantly, resulting in a smaller change in the tear strength of the liquid adhesive.
Add hydrogen terminated methyl silicone oil with different viscosities to the basic formula of liquid adhesive, and discuss its effect on the mechanical properties of liquid adhesive. As the viscosity of hydrogen terminated methyl silicone oil increases, the elongation at break and tear strength of the liquid adhesive gradually increase, while the tensile strength and Shore A hardness gradually decrease. This can be explained as, with the increase of viscosity of end hydrogen methyl silicone oil, i.e. the growth of molecular chains, the molar mass of vinyl silicone oil increases after reacting with end vinyl silicone oil. When cross-linking with multi hydrogen silicone oil, the increase of molecular chains leads to an increase in elongation at break, a decrease in tensile strength and hardness.
Methyl Low Hydrogen silicone oil IOTA203 
