One of the more fascinating puzzles in contemporary polymer science is polydopamine. As you might guess, this is made from polymerizing dopamine, a fairly simple molecule:
Look at this rogues gallery of structures that have been proposed:
Source ($) and Source (OA)
All from such a simple monomer. Heaven forbid someone would want to copolymerize something in along with it.
While polymer science is fairly advanced and the number of good mysteries is being reduced, I'm glad something like this can come along once in a while to keep us on our toes.