A Trinuclear Pd−Diimine Catalyst for “Core-First” Synthesis of Three-Arm Star Polyethylenes via Ethylene “Living” Polymerization

“Core-first” approach for the synthesis of star-shaped polyisoprenes with a branched core and isoprene catalyzed by half-sandwich scandium complexes

Star-shaped polyisoprenes were synthesized by copolymerization of isoprene and branched homopolymer of dimethyl-di-2,4-pentadienyl-(E, E)-silane through “Core-first” approach catalyzed by half-sandwich scandium complex.

New effort to synthesize star isotactic polypropylene

Star isotactic polypropylenes with adjustable arm numbers of 3–8 were synthesized via an efficient arm-first approach with two facile steps.

Boron “stitching” reaction: a powerful tool for the synthesis of polyethylene-based star architectures

Taking advantage of the “stitching” reaction, which transforms the “unstable” boron junction to “stable” carbon, we were able to synthesize novel star block copolymers. This strategy is general and opens new horizons towards unprecedented PE-based materials.

Reversible star assembly of polyolefins using interconversion between boroxine and boronic acid

The reversible star formation of polyolefins, with boronic acid modified chain-ends, was achieved.

"Living" Polymerization of Ethylene and 1-Hexene Using Novel Binuclear Pd⁻Diimine Catalysts

We report the synthesis of two novel binuclear Pd–diimine catalysts and their unique behaviors in initiating “living” polymerization of ethylene and 1-hexene. These two binuclear catalysts, [(N^N)Pd(CH₂)₃C(O)O(CH₂)_mO(O)C(CH₂)₃Pd(N^N)](SbF₆)₂ (3a: m = 4, 3b: m = 6) (N^N≡ArN=C(Me)–(Me)C=NAr, Ar≡2,6–(iPr)₂C₆H₃), were synthesized by simply reacting [(N^N)Pd(CH₃)(N≡CMe)]SbF₆ (1) with diacrylates, 1,4-butanediol diacrylate and 1,6-hexanediol diacrylate, respectively. Their unique binuclear structure with two identical Pd–diimine acrylate chelates covalently linked together through an ester linkage was confirmed by NMR and single crystal XRD measurements. Ethylene “living” polymerizations were carried out at 5 °C and under ethylene pressure of 400 and 100 psi, respectively, with the binuclear catalysts, along with a mononuclear chelate catalyst, [(N^N)Pd(CH₂)₃C(O)OMe]SbF₆ (2), for comparison. All the polyethylenes produced with both binuclear catalysts show bimodal molecular weight distribution with the number-average molecular weight of the higher molecular weight portion being approximately twice that of the lower molecular weight portion. The results demonstrate the presence of monofunctional chain growing species resembling catalyst 2, in addition to the expected bifunctional species leading to bifunctional “living” polymerization, in the polymerization systems. Both types of chain growing species exhibit “living” characteristics under the studied conditions, leading to the simultaneous linear increase of molecular weight in both portions. However, when applied for the “living” polymerization of 1-hexene, the binuclear catalyst 3a leads to polymers with only monomodal molecular weight distribution, indicating the sole presence of monofunctional chain growing species. These two binuclear catalysts are the first Pd–diimine catalysts capable of initiating bifunctional ethylene “living” polymerization.

“Arm-first” approach for the synthesis of star-shaped stereoregular polymers through living coordination polymerization

Stereoregular star polymers were synthesized through an “arm-first” approach via a living coordination polymerization mechanism for the first time using a half-sandwich scandium catalyst system.

Well-defined 4-arm stars with hydroxy-terminated polyethylene, polyethylene-b-polycaprolactone and polyethylene-b-(polymethyl methacrylate)2 arms

Bis-boron-thexyl-silaboracycle was used to initiate the polyhomologation of dimethylsulfoxonium methylide to afford well-defined hydroxy-terminated 4-arm polyethylene (PE) stars, which served as precursors for the synthesis of PE-based starblock copolymers.

New polymethylene-based AB2 star copolymers synthesized via a combination of polyhomologation of ylides and atom transfer radical polymerization

Polymethylene-based AB₂ star copolymers were synthesized. PM-b-(PS)₂ porous films and particles were fabricated via static breath-figure process and electrospraying, respectively.

Synthesis of low dispersity star-like polyethylene: a combination of click chemistry and a sol–gel process

Low dispersity star-like polyethylene was synthesized via a facile sol–gel process using trimethoxysilane-terminated polyethylene derived from thiol-ene click chemistry.

Synthesis of polyethylene and polystyrene miktoarm star copolymers using an “in–out” strategy

Miktoarm star copolymers having multiple polyethylene and polystyrene arms joined at the crosslinked polydivinylbenzene core were synthesized using an “in–out” strategy with the combined Pd-catalyzed ethylene “living” polymerization and atom transfer radical polymerization.