“Living” Polymerization of Ethylene and 1-Hexene Using Novel Binuclear Pd–Diimine Catalysts

Abstract

Abstract: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, [(NˆN)Pd(CH 2 ) 3 C(O)O(CH 2 ) m O(O)C(CH 2 ) 3 Pd(NˆN)](SbF 6 ) 2 (3a: m = 4, 3b: m = 6) (NˆN≡ArN=C(Me)-(Me)C=NAr, Ar≡2,6-(iPr) 2 C 6 H 3 ), were synthesized by simply reacting [(NˆN)Pd(CH 3 )(N≡CMe)]SbF 6 (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, [(NˆN)Pd(CH 2 ) 3 C(O)OMe]SbF 6 (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.

Dual Polymerization Pathway for Polyolefin-Polar Block Copolymer Synthesis via MILRad: Mechanism and Scope

“…During the course of the reaction, the polymerization exhibited a linear increase in molecular weight over time while maintaining narrow polydispersity ( Đ = 1.03–1.11), which indicates a high level of controlled polymerization with negligible chain transfer (Table S30 and Figure S137a,b). To the best of our knowledge, this is one of the rare examples of binuclear palladium catalysts that can achieve this narrow molecular weight distribution ( Đ > 1.46 for other catalysts) …”

Star polyethylenes by coordinative polymerization

“…[ 31 ] 4 was synthesized by reacting 1 with 1,6‐hexanediol diacrylate (HDDA) in large excess ( 1 : HDDA = 1: 10 mol/mol), which promoted the reaction of a single double bond in a diacrylate molecule rather than both. [ 34 ] In 4 , the pendant acryloyl group provides the monomeric site, which is covalently linked to the catalytic Pd‐CH 2 initiating site through the six‐membered chelate structure. [ 31 ]…”

“…[31] 4 was synthesized by reacting 1 with 1,6-hexanediol diacrylate (HDDA) in large excess (1: HDDA = 1: 10 mol/mol), which promoted the reaction of a single double bond in a diacrylate molecule rather than both. [34] In 4, the pendant acryloyl group provides the monomeric site, which is covalently linked to the catalytic Pd-CH 2 initiating site through the six-membered chelate structure. [31] UV-irradiated radical polymerization of 4 with/ without HDDA as a cross-linker was subsequently carried out, leading to the formation of two organometallic polymers: mPd-1 as the homopolymer of 4 and mPd-2 as the copolymer of 4 with HDDA.…”