To what purpose?
If you don't get the raise and you stay, you'll look like a berk.
If you do get one and take it, you just made the first person I'm going to do without list.
If you leave no matter what outcome of the ultimatum, you've just burnt the bridge, the building, and the two little kids on the top floor flat.
If you want a raise, you go for it on the basis of value to your employer, not a higher value somewhere else.
Now if you go to hand in your notice and then you get a counter offer of a raise. That may need some thought. Generally I'm reluctant to take them either, I'd need a lot of convincing, and not just in money, seeing as that has never been why I chose to leave.
