Highly efficient, living coordinative chain-transfer polymerization (CCTP) of propene can be conducted with the highly active catalyst derived from equimolar amounts of (eta s-C5Me5)Hf(Me)(2)[N(Et)C(Me)N(Et)] (2), and the borate, [PhNMe2H][B(C6F5)(4)] (3). In toluene at 0 degrees C, in the presence of varying molar equivalents of ZnEt2 to provide practical quantities (vis-a-vis, living Ziegler-Natta polymerization) of a series of amorphous atatctic polypropene (a-PP) samples. These samples are distinguished by having tunable molecular weights ranging from ultrahigh, in the absence of CCTP, to very high to very low when CCTP is conducted with increasing initial equivalents of ZnEt2-all the while maintaining extremely narrow polydispersities.