Poly(vinylidene chloride) is a polymer that's used for only one thing, but it's an important thing. PVDC, as we call it for short, is the plastic wrap that food comes in at the grocery store, and that you use to wrap up leftovers. Dow Chemical makes this stuff, and calls it Saran®. I'm sure you've heard of it.
The monomer, as you probably guessed, is vinylidene chloride:
Want to see more polymers with Cl or F attached to them? Try these: