Synthesis of Isotactic Polypropylene Containing a Terminal Cl, OH, or NH2 Group via Metallocene-Mediated Polymerization/Chain Transfer Reaction

Abstract

This paper discusses a direct (one-pot) polymerization process to prepare isotactic polypropylene (i-PP) having a terminal functional group including Cl, OH, and NH2. The chemistry involves metallocene-mediated propylene polymerization using rac-Me2Si[2-Me-4-Ph(Ind)]2ZrCl2/MAO complex in the presence of styrene derivatives (St−f), carrying a Cl (St−Cl) or a silane-protected OH (St−OSi) or a silane-protected NH2 (St−NSi2), followed by hydrogenation. Apparently, the propylene propagating chain end engages in a facile consecutive chain transfer reaction, reacting with St−f and then hydrogen, with high catalyst reactivity under the proper St−f and hydrogen concentrations. The polymer molecular weight was inversely proportional to the molar ratio of [St−f]/[propylene] with a chain transfer constant (ktr/kp) of 1/21 for St−Cl, 1/34 for St−NSi2, and 1/48 for St−OSi, respectively. Both silane protecting groups were hydrolyzed in acidic aqueous solution during the sample workup step to obtain the desirable i-PP polymers with a terminal OH and NH2 group (i.e., PP-t-St−OH and PP-t-St−NH2). The terminal functional group was confirmed by end group analysis and chain extension reaction. Despite the high molecular weight, the terminal functional group in PP engages a coupling reaction with polycapolactone (PCL) in solution and melt to form PP-b-PCL diblock copolymers that are very effective compatibilizers in PP/PCL polymer blends.