organosiloxanes

Organosiloxanes are a broad class of organosilicon compounds characterized by backbones of silicon–oxygen–silicon (Si–O–Si) linkages with organic groups attached to silicon. They cover a range of molecular weights and architectures, including linear and branched polymers, cyclic oligomers, and crosslinked networks. The most well-known example is polydimethylsiloxane (PDMS), in which each silicon bears two methyl groups, yielding a flexible, inert material that can exist as a liquid, gum, or elastomer depending on molecular weight and crosslinking.

Synthesis and structure are based on hydrolysis and condensation of chlorosilanes or alkoxysilanes to form siloxane bonds, with water or alcohol as the eliminated byproduct. Circular siloxane monomers can equilibrate to higher molecular weight polymers, and alternative routes such as hydrosilylation or controlled redistribution polymerization enable tailored elastomeric or resinous materials.

Key properties arise from the Si–O–Si backbone: high thermal stability, chemical resistance, and flexibility across a broad temperature range; low glass transition temperatures in many grades; low surface energy and good dielectric and optical properties. Side groups on silicon tune hydrophobicity, refractive index, cure behavior, and mechanical properties.

Applications are diverse and include sealants, structural and electronic adhesives, silicone lubricants, cosmetic and personal-care ingredients, medical devices and implants, pharmaceutical excipients, coatings, and electronics encapsulation and microfluidics.

Safety and environmental notes vary with structure. PDMS and related polymers are widely regarded as biocompatible, but certain cyclic siloxanes raise environmental concerns due to persistence and potential effects in ecosystems. Proper handling and disposal practices are advised.