The interactions of a sterically hindered phenol [2,¿6-¿(t-¿Bu)¿2-¿4-¿Me-¿C6H2OH] (BHT) with the scavenger MAO (AlR3) and ZnR2 during Hf¿/Zr-¿based chain shuttling polymn. in a semi-¿batch reactor have been investigated. NMR model studies indicated preferential binding of BHT to aluminum under these conditions. Subsequently, reproducible polymn. runs gave rise to copolymers that were thoroughly characterized by HT-¿SEC, HT-¿HPLC, DSC, thermal fractionation (SSA)¿, 13C NMR, d. measurements, CRYSTAF and optical microscopy to unravel their complex microstructures. The obtained materials differ from a simple soln. blend of materials, sep. produced by single catalysts, but also from multi-¿block copolymers as obtained by DOW's continuous process, although a blocky structure can be rationalized.