Substantially isotaclic propylene interpolyraets comprise (A) at least 60 weight percent (wt %) units derived from propylene, and (B) between greater than zero and 40 wt % units derived from ethylene, the propylene interpolyrner further characterized by at least one of the following properties: (1) a ratio of less than 1 measured at interpolyraer number average molecular weight (Mn), (2) a relative compositional drift of less than 50%, arid (3) propylene chain segments having a chain isotacticity triad index of at least 70 mole percent.