Is it possible to use your reach weapon as an improvised quarterstaff to threaten adjactend squares?
If it is possible there is the feat Catch Off-Guard to negate the -4 penalty for improvised weapons.
The Polearm Masteron the other hand needs to use an immediate action to attack adjacent squares with a -4 penalty. (and can only negate that penalty by 18th level?!)
Of course he deals full damage, when an improvised quarterstaff would only deal its 1d6... but still
If possible (answer unclear, ask again later), improvised weapon (not quarterstaff specifically) would deal 1d6, and not gain any benefit from weapon focus, weapon specialization, weapon training, improved critical, etc.
Personally I see no reason you couldn't use a polearm improvised to attack adjacent squares, but it should be a move action to change the way you are wielding it to do so. You wouldn't threaten with it at 5' while wielding it normally.
I think you have the right of it. If you just want to pick up the pole arm and smack someone with the haft, it's improvised and hits like a club. If you want to be trained to use the business end and get the versatility of any descriptors the weapon has (other than bludgeon) it is a feat and still not easy.
I guess the question is, can you make improvised attacks with the haft of a polearm, take the penalty, and not take the polearm master feat or take Catch off guard and do so without penalty. Either option would be fine at my table, but someone else might have a different insight.