There are many types of organic silicone products, and they are ever-changing, but the vast majority of organic silicone products are generated from the most basic intermediates through grafting reaction, etc. It is octamethylcyclotetrasiloxane, commonly known as D4.
Octamethylcyclotetrasiloxane (D4) is a colorless, transparent or opalescent liquid, flammable, and has no odor. It is a product obtained from dimethyldichlorosilane through a hydrolysis and synthesis process, and has been separated and distilled. The obtained compound is an important intermediate in the silicone industry. Rings similar to D4 include D3/D5/D6. If these are mixed with D4, it is often called DMC.
Click for detailed information: Octamethylcyclotetrasiloxane IOTA D4 – (iotachem.com)