According to "Tracing the History of Polymeric Materials, Part 25: Silicones"; Michael Sepe (Plastics Technology, 01/12/2023):
"In 1969, Neil Armstrong stepped onto the lunar surface wearing boots with soles made from silicone."
A concise, well written history of polymers. Check it out.
Here's the Response from ChatGPT (AI):
"Yes, Neil Armstrong did step onto the lunar surface wearing boots with soles made from silicone during the Apollo 11 mission in 1969.
The boots used by the astronauts, known as Apollo/Skylab A7L Extravehicular Mobility Unit (EMU) boots, had silicone rubber soles. These boots were specifically designed to provide traction and flexibility for the astronauts during their lunar activities.
The silicone rubber soles helped them grip the lunar surface and provided some protection against extreme temperatures and potential hazards on the moon."
Image from the US Airforce Museum (1971)