Borane-terminated isotactic polypropylene

In a recent development, a new process of preparing borane-terminated isotactic polypropylene (z -PPs) via an in situ chain-transfer reaction was achieved by a styrene/hydrogen consecutive chain-transfer reagent, which avoids the use of a B—H containing chain-transfer agent.74 This has resulted in the utilization of milder polymerization conditions due to the use of the alkylaluminoxane cocatalyst (MAO) (50) (Fig. 33), which cannot normally be used in the presence of a B—H chain-transferring... 

In the absence of hydrogen, metallocene-based catalyst systems produce well-defined polymers which are olefin- or aluminum-terminated. Miilhaupt has polymerized propylene with a chiral metallocene and MAO under conditions where P-hydrogen elimination was the predominant chain transfer process. In a post-polymerization functionalization, the olefin endgroups of the highly isotactic polypropylene chains were converted to bromo-, epoxy-, anhydride-, ester-, amine-, carboxylic acid-, silane-, borane-, hydroxy-, thiol-terminated polymers as intermediates for the preparation of block copolymers. Using olefin-terminated atactic and isotactic polypropylene formed with MAO-activated Cp2ZrCl2 and (EBTHI)ZrCl2 Shiono has synthesized amine- and aluminum-terminated polymers." ... 

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