The best you can do between touch down of the plane and leaving the Terminal is around 40 minutes, it could be much longer if some other flights are arriving just before yours. The UA terminal is on the other side of the U shaped road at LAX, so either take the bus (20 min waiting max, 10 min drive) or walk across (10 min).
Then you need time at the UA terminal for check in etc - so 2 hours is very, very tight but not impossible if everything goes well.
I would not risk it.

Domestic to international should be ok.