Living and block copolymerization of ethylene and α-olefins using palladium(II)-α-diimine catalysts

Living polymerizations of ethylene with palladium(II) diimine complexes coupled with use of a functionalized initiator and/or cleavage of the palladium-polymer bond with various reagents provides a protocol for synthesis of mono- and di-end-functionalized, branched, amorphous polyethylenes. The functional initiator used is the chelate complex [(ArN=C(Me)-C(Me)=NAr)Pd)(CH2)(3)C(O)OMe] [(BAr'(4))] (Ar = 2,6-(iPr)(2)C6H3) (3). The alkyl chain is cleaved by insertion of alkyl acrylates or methyl vinyl ketone, followed by cleavage with Et3SiH to generate alkyl ester or methyl ketone end groups, respectively. Insertion of 5-hexen-1-ol, followed by chain running and beta-elimination, results in formation of aldehyde end groups. Conditions for living polymerization of propylene, 1-hexene, and 1-octadecene have also been established. Rates of first monomer insertion and subsequent chain growth are shown to be a sensitive function of the palladium complex used for initiation and the nature and concentration of auxiliary nitrile ligands. Block copolymers of ethylene and 1-octadecene were prepared under living conditions. The copolymer microstructure differed depending on the order of introduction of the blocks.