SOME rubber. Not the synthetic stuff used in brake calipers or what would be the point in using it? But brake cleaner sure does a number on tire rubber.

None of our chains would be lined with any sort of plastic or teflon since that would allow some amount of compression which under high load would make the chain stretch a little and the links would no longer fit the sprocket pitch. THAT would wear out the chain and sprockets double quick. Some may have some sort of "coating" but it will be micro thin as opposed to any sort of bushing such as you're thinking about.