High Temperature, Living Polymerization of Ethylene by a Sterically-Demanding Nickel(II) α-Diimine Catalyst.

Catalysts that employ late transition-metals, namely Ni and Pd, have been extensively studied for olefin polymerizations, co-polymerizations, and for the synthesis of advanced polymeric structures, such as block co-polymers. Unfortunately, many of these catalysts often exhibit poor thermal stability and/or non-living polymerization behavior that limits their ability to access tailored polymer structures. Due to this, the development of catalysts that display controlled/living behavior at elevated temperatures is vital. In this manuscript, we describe a Ni α-diimine complex that is capable of polymerizing ethylene in a living manner at temperatures as high as 75 °C, which is one of the highest temperatures reported for the living polymerization of ethylene by a late transition metal-based catalyst. Furthermore, we will demonstrate that this catalyst's living behavior is not dependent on the presence of monomer, and that it can be exploited to access polyethylene-based block co-polymers.

Accessing Siloxane Functionalized Polynorbornenes via Vinyl-Addition Polymerization for CO2 Separation Membranes.

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.

Effect of Cross-Link Density on Carbon Dioxide Separation in Polydimethylsiloxane-Norbornene Membranes.

The development of high-performance materials for carbon dioxide separation and capture will significantly contribute to a solution for climate change. Herein, (bicycloheptenyl)ethyl-terminated polydimethylsiloxane (PDMSPNB) membranes with varied cross-link densities were synthesized via ring-opening metathesis polymerization. The developed polymer membranes show higher permeability and better selectivity than those of conventional cross-linked PDMS membrane. The achieved performance (CO2 permeability≈6800 Barrer; CO2 /N2 selectivity≈14) is very promising for practical applications. The key to achieving this high performance is the use of an in situ cross-linking method for difunctional PDMS macromonomers, which provides lightly cross-linked membranes. By combining positron annihilation lifetime spectroscopy, broadband dielectric spectroscopy, and gas solubility measurements, key parameters necessary for achieving excellent performance have been elucidated.