A series of isotactic polypropylene (iPP) and polyethylene (PE) diblock, tetrablock, and hexablock copolymers (BCPs) were synthesized with tunable molecular weights using a hafnium pyridylamine catalyst. The BCPs were melt blended with 70 wt % high-density PE (HDPE) and 30 wt % iPP commercial homopolymers at concentrations between 0.2 and 5 wt %. The resulting blend morphologies were investigated using TEM, revealing uniformly dispersed iPP droplets ranging progressively in size with increasing BCP content from three-quarters to one-quarter of the diameter of the uncompatibilized mixture. Tensile tests revealed a dramatic enhancement in toughness based on the strain at break which increased from 10% for the unmodified blend to more than 300% with just 0.2 wt % BCP and over 500% with the addition of 0.5 wt % BCP or greater. Incorporation of BCPs in blends also improved the impact toughness, doubling the Izod impact strength to a level comparable to the neat HDPE with just 1 wt % additive. These improved blend properties are attributed to enhanced interfacial strength, which was independently probed using T-peel adhesion measurements performed on laminates composed of HDPE/BCP/iPP trilayers. Thin (ca. ≤100 nm thick) BCP films, fabricated by high-temperature spin coating and molded between the homopolymer films, significantly altered the laminate peel strength, depending on the molecular weight and molecular architecture of the block copolymer. Multilayer laminates containing no BCP or low molecular weight diblock copolymer separated by adhesive failure during peel testing. Sufficiently high molecular weight iPP–PE diblock copolymers and iPP–PE–iPP–PE tetrablock copolymers with significantly lower block molecular weights exhibited cohesive failure of the HDPE film rather than adhesive failure. We propose adhesion mechanisms based on molecular entanglements and cocrystallization for tetrablocks and diblocks, respectively, to account for these findings. These results demonstrate exciting opportunities to recycle the world’s top two polymers through simple melt blending, obviating the need to separate these plastics in mixed waste streams.

While traditional polymerization of linear α-olefins (LAOs) typically provides amorphous, low T(g) polymers, chain-straightening polymerization represents a route to semicrystalline materials. A series of α-diimine nickel catalysts were tested for the polymerization of various LAOs. Although known systems yielded amorphous or low-melting polymers, the "sandwich" α-diimines 3-6 yielded semicrystalline "polyethylene" comprised primarily of unbranched repeat units via a combination of uncommon regioselective 2,1-insertion and precision chain-walking events.

We have developed a method for direct, copper-catalyzed, auxiliary-assisted fluorination of β-sp2 C-H bonds of benzoic acid derivatives and γ-sp2 C-H bonds of α,α-disubstituted benzylamine derivatives. The reaction employs CuI catalyst, AgF fluoride source, and DMF, pyridine, or DMPU solvent at moderately elevated temperatures. Selective mono- or difluorination can be achieved by simply changing reaction conditions. The method shows excellent functional group tolerance and provides a straightforward way for the preparation of ortho-fluorinated benzoic acids.

The compatibilization of polyethylene (PE) and isotactic polypropylene (iPP) blends is of particular interest due to the challenges associated with recycling these plastics from mixed waste streams. Polyethylene-graft-iPP copolymers (PE-g-iPP) were prepared using a grafting-through strategy by copolymerization of ethylene with allyl-terminated iPP macromonomers in the presence of a hafnium pyridylamido catalyst. Graft copolymers with a variety of graft lengths (M n = 6–28 kg/mol), graft numbers, and graft spacings were prepared. These graft copolymers were melt-blended with high-density polyethylene (HDPE) and iPP (iPP/HDPE = 30/70 w/w), and the blend properties were evaluated by tensile testing. The blends showed enhanced tensile strength at 5 and 1 wt % loading, with higher tensile strength observed for larger block numbers and graft lengths. These results indicate that graft copolymers are efficient compatibilizers for blends of HDPE and iPP.

Nickel α-diimine catalysts have been previously shown to perform the chain straightening polymerization of αolefins to produce materials with melting temperatures (T m ) similar to linear low density polyethylene (T m = 100−113 °C). Branching defects due to mechanistic errors during the polymerization currently hinder access to high density polyethylene (T m = 135 °C) from α-olefins. Understanding the intricacies of nickel α-diimine catalyzed α-olefin polymerization can lead to improved ligand designs that should allow production of chain-straightened polymers. We report a 13 C NMR study of poly(α-olefins) produced from monomers with 13 C-labeled carbonsspecifically 1-decene with a 13 C-label in the 2-position and 1-dodecene with a 13 C-label in the ω-positionusing a series of α-diimine nickel catalysts. Furthermore, we developed a mathematical model capable of quantifying the resulting 13 C NMR data into eight unique insertion pathways: 2,1-or 1,2insertion from the primary chain end position (1°), the penultimate chain end position (2 p °), secondary positions on the polymer backbone (2°), and previously installed methyl groups (1 m °). With this model, we accurately determined overall regiochemistry of insertion and overall preference for primary versus secondary insertion pathways using nickel catalysts under various conditions. Beyond this, our model provides the tools necessary for determining how ligand structure and polymerization conditions affect catalyst behavior for α-olefin polymerizations.