You need more than a contract drawn up by divorce lawyers. No guarantee he'll keep his word about signing it.
You need some kind of proof of the abuse. Even if you go talk to a doctor or a therapist/psych so it's documented somewhere and someone professional is on your side.
Rich guys can get out of contracts somehow.. make sure you know what you're doing there.
and what if he refuses to sign it and threatens to take the baby instead? He has money.. you don't..
Any documented bruises/whatever from him hitting you by your regular dr? Any ER visits?
Makes sense to stay with him and play along until you can get out of there but you need a better backup plan. It doesn't matter how he reacts if the plan is good.