Regardless of difficulty, the Ai empires trade tech to each other with only volume of techs in mind. They're not careful like humans are. They'll trade anything to anyone. Pretty much every game I play, by turn 150 or so, all the Ai empires have traded each other most of their tech. (tech brokering disabled).
Think of the way you trade. When you get a tech you want to trade, you trade it to each civ you have met. Assuming you get 1 tech in exchange and there's 7 opponents, you've researched 1 tech and gained 7 more. Now imagine if you didn't care what you traded and did that every chance you got. You get a lot of tech pretty quick, so it *looks* like you're a research monster, but it's just an illusion 
