http://kompozite.com/2011-08-08/silicone.html
1. Polydimethylsiloxane
Polydimethylsiloxanes, shortly called silicones, are very versatile raw materials which can exhibit a variety of properties dependent on their molecular structure. Silicones are used in paint additives for example as:
• defoaming and de-aerating agents
• slip additives
• wetting agents
• levelling agents
• hammer finish agents
The principal reasons for the wide spectrum of uses of silicones as components in the production of paint additives are:
• low surface tension
• excellent lubricating
• slip properties
The surface tension of silicones is around 20 mN/m, which means that silicones quickly form a film at interfaces, when introduced into a liquid.
Differently structured silicones form films at the interface between substrate and coating and promote wetting of the substrate. Similarly specially selected silicones move to the air/liquid paint interface where they destabilise the air bubbles and cause them to burst. After application of a coating system this film is formed on the surface and produces a slip effect.
The possible application of silicones depends very much on their molecular structure and molecular mass. The basic building brick of all silicones is polydimethylsiloxane which has the molecular structure:
The following table presents a summary of these relationships displayed by polydimethylsiloxanes: 
Polydimethylsiloxanes distinguish themselves only by the length of the polymer chain (i.e. magnitude of "x"). The average molecular mass (or the viscosity) is a measure of the length of the polymer chain (i.e. degree of polymerisation). The properties of these silicones with a simple structure depend therefore solely on the molecular mass.
2. Modified polydimethylsiloxanes
By chemical modifications of the molecular structure of polydimethylsiloxanes, modified silicones with new properties are obtained. A schematic chemical formulation of such modified silicones is shown in the following illustration:
The organic modification can represent any desired molecular grouping with the exception of the alkyl group ( -CH3).
The properties of these silicone products depend on three factors:
• type of organic modification
• relation of the x- and y-units
• molecular mass
3. Silicone copolymers
Silicone co-polymers are compounds, which combine the properties of silicones with those of the corresponding co-polymer. This combination creates products with new interesting properties.
They minimise the risks incurred by accidental excessive dosage of ‘normal’ silicone oils like
• cratering
• poor adhesion
• recoating problems
• incompatibility in systems
Polyethers or polyesters are frequently used as the co-polymer component. The schematic chemical structure of silicone copolymers is:
Planned chemical synthesis can produce exactly the desired properties of silicone co-polymers. The m-unit is the hydrophilic organic component, the n-unit the hydrophobic organic component and the p-unit contributes the typical properties characteristic of the silicone co-polymer. The m-n-p-mass ratio therefore determines the overall properties of the silicone co-polymer.
