Dimethylsiloxane

Dimethylsiloxane refers to a siloxane compound in which silicon atoms are linked by oxygen atoms and bear two methyl groups each. In practice, the term is often used to describe the repeating unit –Si(CH3)2–O– that forms polydimethylsiloxane (PDMS). Thus, dimethylsiloxane can describe either the siloxane monomeric unit or, more commonly, the polymeric material PDMS, which consists of many such units arranged in a chain with various end groups.

Preparation and structure

PDMS is produced by hydrolysis and polycondensation of dimethyldichlorosilane or by polymerizing cyclic siloxanes derived from dimethylsiloxane units. The result is a family of silicone polymers with a Si–O–Si backbone and methyl groups attached to silicon. The length of the chain and the nature of end groups give rise to a range of materials from low-viscosity liquids to high-strength elastomers.

Properties

Dimethylsiloxane–based polymers exhibit high thermal stability, wide operating temperature ranges, and very low glass transition temperatures. They have low surface energy, high flexibility, and excellent chemical and environmental inertness. PDMS is typically hydrophobic, optically clear, and highly permeable to gases. Its dielectric constant is low, making it useful in electrical and electronic applications.

Applications and use

PDMS and related dimethylsiloxanes are employed as lubricants, sealants, elastomers, and cosmetics ingredients. They are widely used in medical devices and implants, microfluidics, and a variety of industrial coatings. In research, PDMS is a common substrate for microfabricated channels and soft lithography.

Safety

PDMS is generally regarded as biologically inert and has low acute toxicity. Some low‑molecular‑weight siloxanes and residual cyclic oligomers can raise regulatory or irritation concerns in certain uses, particularly in cosmetics or environmental contexts.