Catalytic Chain Transfer Polymerization to Functional Reactive End Groups for Controlled Free Radical Growth

Alkoxyamine-functionalized silane functions as a chain transfer reagent in ethylene polymerization catalyzed by cationic palladium diimine complexes, without significant adverse effects in productivity or yield. Under conditions of limited chain transfer by beta-hydride elimination, this approach highly selectively results in alkoxyamine-terminated hyperbranched poly-ethylenes (PEs) and multiple (up to 5) functionalized PE chains per active metal site. Stoichiometric NMR spectroscopic investigations indicate that the first chain transfer generates a saturated chain end, while all following polymer chains are initiated by (functionalized) silyl groups. Alkoxyamine-functionalized hyperbranched PEs obtained by this approach are suitable precursors for nitroxide-mediated radical polymerizations. This allows for harnessing different chain growth mechanisms (catalytic insertion/free radical) for generation of PE-polyacrylate and PE-polystyrene block copolymers.