In "loose cannons", there were two instances of small talk that let on a bit of the characters more private personality. Megatron casual conversation with Soundwave indicated a sort of camaraderie or private understanding, but Prime's conversation with Wheel Jack aboard the Star Hammer showed that Prime is really still the archivist, he is dull because he's basically a librarian with high sense of morality; given incredible strength and wisdom through the matrix. He probably didn't socialize much in his previous position. Which ultimately showed itself when he asked wheel jack about "going it alone." (The awkwardness since Prime doesn't know how to relate was telling). If Prime becomes more charismatic it will be a major change in his character. This is in response to all the "Prime is dull complaints" I think the dull part is an important part of his character.