•Poly((5-triethoxysilyl-2-norbornene) is a mechanically and thermally robust membrane material.•This polymer has high permeability for many target gases.•This polymer exhibits reverse, or solubility controlled, selectivity which is unusual for glassy polymers.•This polymer has low fractional free volume compared to most other glassy polymers.•This polymer displays pressure dependent gas diffusion intermediate between those of typical glassy or rubbery materials.Poly(5-triethoxysilyl-2-norbornene) was prepared in good yield (71%) by vinyl-addition polymerization using the catalyst trans-Ni(C6F5)2(SbPh3)2. This polymer is completely amorphous and has a high glass transition temperature (325 °C). Investigation of its gas permeation parameters revealed that it has relatively high gas permeability for a variety of gases (e.g. P(O2) = 211 Barrer). A unique feature of poly(5-triethoxysilyl-2-norbornene) is that it is a glassy material that exhibits solubility controlled permeation of hydrocarbons, a feature that is commonly only found in rubbery polymers and polymers with extremely large free volume (e.g. poly[(trimethylsilyl)propyne]. The permeability coefficient of butane in this polymer (P(C4H10)) is as high as 5 × 103 Barrer, whereas its butane/methane selectivity (P(C4H10)/P(CH4)) is 21 ± 3. Analysis of poly(5-triethoxysilyl-2-norbornene)'s permeability coefficients, diffusion coefficients, solubility coefficients, and free volume demonstrate that this polymer combines the attractive properties of both a rubbery polymer and a glassy polymer.Download high-res image (63KB)Download full-size image

The ability to control catalytic activity via redox-activity has had a significant impact on the field of polymerization catalysis. Herein, we describe the synthesis of three unique Ni-based olefin polymerization catalysts bearing redox-active α-diimine ligands. We will demonstrate that catalysts bearing butanedione- or glyoxal-derived ligands display little to no differentiation as a function of redox-state. However, in stark contrast we will show that the catalyst bearing an acenaphthenequinone-derived ligand is capable of producing either medium-density or very-low-density polyethylene based purely on its ligand-based redox-state. This ability to access more than one polyethylene grade via a single redox-active catalyst is unprecedented.

The ability to control catalytic activity and selectivity via in situ changes in catalyst oxidation-state represents an intriguing tool for enhanced polymerization control. Herein, we report foundational evidence that catalysts bearing redox-active moieties may be used to synthesize high molecular weight polyethylene with tailored microstructure. The ability to modulate branching density and identity is facilitated by ligand-based redox chemistry, and is realized via the addition of chemical reductants into the polymerization reactor. Detailed GPC and NMR analyses demonstrate that branching density may be altered by up to ∼30% as a function of in situ added reductant.

The ability to precisely modulate polymer architecture and composition is a long-standing goal within the field of polymer synthesis. Herein, we demonstrate that redox-active olefin polymerization catalysts may be used to predictably tailor polyolefin comonomer incorporation levels for the copolymerization of ethylene and higher α-olefins. This ability is facilitated via the utilization of a redox-active olefin polymerization catalyst that once reduced via in situ addition of a chemical reductant results in a notable drop in α-olefin incorporation. We attribute this behavior to the reduced catalyst’s increased electron density and its concomitant decreased rate of α-olefin consumption. These results are supported by investigations into propylene and 1-hexene homopolymerizations as well as detailed GPC, DSC, GC, and NMR analyses.

The vinyl addition polymerization of norbornyl-based monomers bearing polar functional groups is often problematic, leading to low molecular weight polymers in poor yield. Herein, we provide proof-of-principle evidence that addition-type homopolymers of siloxane substituted norbornyl-based monomers may be readily synthesized using the catalyst trans-[Ni(C6F5)2(SbPh3)2]. Polymerizations using this catalyst reached moderate to high conversion in just 5 min of polymerization and produced siloxane-substituted polymers with molecular weights exceeding 100 kg/mol. These polymers showed excellent thermal stability (Td ≥ 362 °C) and were cast into membranes that displayed high CO2 permeability and enhanced CO2/N2 selectivity as compared to related materials.

A titanium(IV) salfen catalyst bearing a redox-active ferrocenyl center in close proximity to the active metal site was examined for the redox-switchable polymerization of l-lactide. The catalyst displayed an atypical β-cis geometry in both the solid- and solution-states, and placement of the redox-active moiety in close proximity to the active metal site was shown to provide an enhancement in catalytic “on–off–on” switching behavior when the redox events were performed in the presence of lactide monomer. More importantly, when comparing oxidized and reduced catalytic species, completely contrasting trends in polymerization behavior were observed, depending on whether the catalyst was oxidized in the absence or in the presence of lactide monomer. On the basis of NMR spectroscopic analysis, we propose that this unusual behavior is a result of a rapid switch in ligand coordination geometry that is facilitated by monomer coordination prior to any redox reactions. Additionally, when redox reactions were conducted in the absence of monomer, a trend in activity that contradicted those of all previously reported Ti-based redox-active catalysts was observed.Keywords: l-lactide; oxidation; polyester; polymerization; redox-active; reduction; titanium

A series of highly enantioselective transformations, such as the Sharpless asymmetric epoxidation and Jacobsen hydrolytic kinetic resolution, were utilized to achieve the complete stereoselective synthesis of β-O-4 lignin dimer models containing the S, G, and H subunits with excellent ee (>99%) and moderate to high yields. This unprecedented synthetic method can be exploited for enzymatic, microbial, and chemical investigations into lignin’s degradation and depolymerization as related to its stereochemical constitution. Preliminary degradation studies using enantiopure Co(salen) catalysts are also reported.

Sterically demanding 2,6-bis(diphenylmethyl)-4-methylaniline was condensed onto acenaphthenequinone via an aminoalane intermediate and metalated using nickel(II) dibromide dimethoxyethane adduct to yield bis[(2,6-dibenzhydryl-4-methylimino) acenaphthene]dibromo nickel(II). This α-diimine precatalyst was examined for high-temperature ethylene polymerization and proved to be thermally robust at temperatures as high as 90 °C, demonstrating enhanced activity as compared with related catalysts. Furthermore, the resultant polymers displayed increased melting transitions as compared with those produced using catalysts with identical N-aryl moieties appended to nonacenaphthenequinone-derived ligand backbones.Keywords: catalysis; coordination polymerization; high temperature; nickel; polyethylene; α-diimine

Sterically demanding NiII α-diimine precatalysts were synthesized utilizing 2,6-bis(diphenylmethyl)-4-methyl aniline. When activated with methylaluminoxane, the catalyst NiBr2(ArN═C(Me)–C(Me)═NAr) (Ar = 2,6 bis(diphenylmethyl)-4-methylbenzene) was highly active, produced well-defined polyethylene at temperatures up to 100 °C (Mw/Mn = 1.09–1.46), and demonstrated remarkable thermal stability at temperatures appropriate for industrially used gas-phase polymerizations (80–100 °C).

The ability to control catalytic activity via redox-activity has had a significant impact on the field of polymerization catalysis. Herein, we describe the synthesis of three unique Ni-based olefin polymerization catalysts bearing redox-active α-diimine ligands. We will demonstrate that catalysts bearing butanedione- or glyoxal-derived ligands display little to no differentiation as a function of redox-state. However, in stark contrast we will show that the catalyst bearing an acenaphthenequinone-derived ligand is capable of producing either medium-density or very-low-density polyethylene based purely on its ligand-based redox-state. This ability to access more than one polyethylene grade via a single redox-active catalyst is unprecedented.