Living polymerizations of propylene and syntheses of atactic polypropylene-block-poly(ethylene-co-propylene) using metallocene catalyst systems Original Research Article

Living propylene polymerizations were performed with various metallocene catalyst (Mt=Zr and Hf)/cocatalyst (organoborane)/trialkylaluminium systems at low temperatures, i.e. Cp2ZrR2 (Cp=cyclopentadienyl, R=Me and Cl)/B(C6F5)3/AlR3′ (R′=octyl and iso-butyl) at −78 °C, Cp2HfMe2/B(C6F5)3/AlOct3 at −50 °C and Cp2∗HfMe2 (Cp∗=pentamethylcyclopentadienyl)/B(C6F5)3/AlOct3 at −78 °C. The Cp2∗HfMe2 system showed a considerably higher propagation rate than the Cp2ZrR2 or Cp2HfMe2-based systems. With the above metallocene catalyst systems, atactic polypropylene-(ethylene-co-propylene) (ataPP/EP) block copolymers were prepared by the addition of ethylene monomer during the living polymerization of propylene at low temperature. By the addition of ethylene, the Mn for the resultant copolymer showed a higher value than that of corresponding homopolypropylene while retaining the narrow molecular weight distribution. By the transmission electron microscopy (TEM) analysis, a microphase-separated morphology with ca. 50–100 nm dimension was observed in an iso-PP/PP-block-EP blend.