I'll say that the "po" of "sciences politiques" and "sciences po" sounds the same in french [pɔ]. Maybe you think that it's sound differently because in "sciences po" you finish your word on an "o" sound, so you may hear an emphasize on the "o".

I'll say that the "po" of "sciences politiques" and "sciences po" sounds the same in french [pɔ]. Maybe you think that it's sound differently because in "sciences po" you finish your word on an "o" sound, so you may perceive the pronunciation of this o as if it were emphasized.