Addition-Cure Silicone Systems Explained

1. How Does Addition-Cure Silicone Rubber Cure?

The key reaction in addition-cure silicone is hydrosilylation.

In a typical system, a vinyl-functional silicone reacts with a silicone containing Si–H groups in the presence of a platinum catalyst.

The simplified reaction can be represented as:

As the reaction proceeds, different silicone molecules become connected and gradually form a three-dimensional crosslinked network.

The material therefore changes from a flowable formulation into an elastic silicone rubber.

For a closer explanation of the roles of the two key silicone materials, see:

2. What Are the Main Components?

A typical addition-cure silicone formulation may contain:

The exact formulation varies according to the intended product.

For example, LSR formulations emphasize fast molding and production efficiency, while RTV-2 systems may place greater emphasis on working time, storage stability and curing behavior after mixing.

3. Vinyl Silicone Oil as the Base Polymer

Vinyl Silicone Oil is commonly used as the base polymer in addition-cure silicone systems.

Its vinyl groups provide the reactive sites required for hydrosilylation.

The vinyl content, molecular structure and viscosity can all affect processing and the final crosslinked network.

Different grades of Vinyl Silicone Oil can therefore be used for applications such as:

4. Methyl Hydrogen Silicone Fluid as the Crosslinking Component

Methyl Hydrogen Silicone Fluid provides Si–H groups for the hydrosilylation reaction.

In a typical addition-cure formulation:

These two components are not simply mixed according to a universal weight ratio.

The formulation needs to consider the functional-group content of both materials and the desired crosslink density.

5. The Role of Platinum Catalyst and Inhibitor

A platinum catalyst is an important component of many addition-cure silicone systems.

Its activity can influence:

If the reaction is too fast, premature curing may occur during processing. If the reaction is too slow, production efficiency and final curing may be affected.

Inhibitors can therefore be used to control reaction behavior and provide an appropriate processing window.

The formulation needs to balance:

6. Formulation Design

Several parameters need to be considered when designing an addition-cure silicone formulation.

Vinyl-to-Si–H Ratio

The relationship between vinyl groups and Si–H groups affects the crosslinked structure.

An unsuitable ratio may result in incomplete curing or changes in final hardness and other properties.

Base Polymer Viscosity

Viscosity affects mixing, flow, deaeration and molding behavior.

Catalyst Level

Catalyst concentration directly influences reaction speed.

Inhibitor Level

Inhibitors help control the working window and storage stability.

Fillers

Fillers can affect viscosity, hardness, strength and appearance.

For this reason, addition-cure silicone should be designed as a complete formulation rather than by considering one silicone raw material in isolation.

7. Addition-Cure Silicone Production Process

A typical production process can be summarized as:

In two-component RTV-2 systems, reactive components are generally packaged separately and mixed before use.

In LSR production, precision metering, mixing and molding equipment can be used for continuous processing.

Uniform mixing is particularly important.

Uneven distribution of the catalyst, crosslinker or fillers can lead to differences in local curing behavior and affect hardness, surface quality and mechanical performance.

For a more detailed explanation of how Vinyl Silicone Oil and Hydrogen Silicone Oil are used in silicone rubber production, see:

8. Addition-Cure vs Condensation-Cure Silicone

Addition-cure and condensation-cure silicones can both be used for sealing, molding and industrial applications, but their curing mechanisms are different.

The appropriate system depends on the formulation, processing method and required final properties.

9. How Is OH Polymer Different?

OH Polymer, also known as hydroxyl-terminated PDMS, is another important silicone base material.

Its curing chemistry differs from that of the typical addition-cure system based on vinyl silicone and Si–H silicone.

Addition-cure systems mainly rely on:

OH Polymer is commonly associated with condensation-cure silicone systems.

Therefore, when developing silicone rubber or RTV formulations, the base polymer should be selected according to the required curing mechanism, processing method and final properties.

For more information about OH Polymer, see:

10. Applications of Addition-Cure Silicone

Addition-cure silicone systems can be used in a wide range of applications.

11. Factors Affecting Final Performance

The final properties of silicone rubber depend on more than the base polymer.

Important factors include:

Stable silicone rubber production therefore requires good coordination between raw materials, formulation design and manufacturing conditions.

12. Organosilicon Supply from Bayee Chemical

Bayee Chemical supplies a range of organosilicon products for silicone rubber, industrial processing, electronic materials and other applications.

For addition-cure silicone systems, raw material selection should consider viscosity, functional-group content, purity, batch consistency and compatibility between different formulation components.

Selecting suitable Vinyl Silicone Oil, Hydrogen Silicone Fluid and related organosilicon materials according to the actual formulation and manufacturing process can help establish a more consistent production system.

Conclusion