Polysiloxanes (Silicones)

Properties and Applications

Silicones or polydialkylsiloxanes are the most important class of inorganic polymers. They are known for their high temperature and oxidative stability, excellent low temperature flexibility, low friction, and high resistance to weathering and many chemicals.
The name silicone usually refers to organosilicon polymers with the general structure -[Si(R₂)-O]- where R = -CH₃ is called poly(dimethyl siloxane) which is often abbreviated as PDMS. It has one of the lowest critical surface tension of all polymers and is capable of wetting most materials. The methyl groups along the chain can be substituted by many other groups (e.g., ethyl, phenyl, vinyl, etc.) which allows for tailoring the chemical, mechanical and thermophysical properties for a wide variety of applications. The terminal silanol end groups render silicones susceptible to condensation under both mild acid and base conditions. These resins are either intermediates for room temperature vulcanizeable silicones (RTVs) or are converted to many silicone products.

PDMS and its copolymers have a broad range of applications across almost all industries including protective coatings, sealants, adhesives, surfactants, pressure sensitive tapes, antifoam agents, silicone fluids, textile finishes, rubber molds, elastomeric gaskets and seals, release coatings for transfer paper and release liner (silicone-coated paper) and as the active ingredient in many spray-on mold release agents. In a variety of applications, siloxanes are incorporated into other polymers to improve certain properties such as oxygen permeability, release, or low temperature flexibility. For some other applications, polymers such as urethanes or polyethers are functionalized with (methoxy)silane groups. These resins are sometimes referred to as silyl-modified oligomers.¹ They combine the typical advantages of silicones and the host polymer.

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