Using Polyurethane On Outdoor Furniture?

I am guessing you want to paint a table with polyurethane. If so you can but the sun may cause the urethane to become milky and peel. Why not paint a board and then put urethane over the color coat and leave it in the sun and see what happens.

You might want to check with a marine supply/maintenance store. Boats are in the wet and they have been wooden. What do they use on their decks? Good Luck!