You COULD, but would you want to?
That's at least a 6 hour trip ... if everything is right. And you are a swift driver.
Turn in the rental at Sea Tac and puddle jump it down to PDX. Spendy, but doable.
More practacle.. Drive to Portland the day before. Any of the airport located hotels are fine and reasonably priced. Stay out of the ones on 82nd Ave. or Sandy Blvd. Anything on Airport Way should be fine.
Do this and get some