Biaxial melt-drawing of blend films composed of ultra-high molecular weight polyethylene and normal molecular weight polyethylene produced a unique network structure consisting of 30-nm thick homogeneous folded chain crystals. Subsequent biaxial solid-drawing produced a nanoporous structure covering a large area of the membrane surface (120 mm × 120 mm). Effects of preparation parameters, including annealing and subsequent solid-drawing, on resultant nanoporous morphology are also testified to achieve the desirable membrane. The higher gas permeability coefficients of the nanoporous membranes indicate that these nanopores are interconnected along the thickness direction. Despite such excellent porosity, the tensile strength reached 30 MPa, which is similar to that for the initial non-porous film. Consistence of membrane porousness and robustness is highly desirable for various separation applications, including filtration, water purification, dialysis, and lithium-ion batteries.
Various transition metal catalysts have been utilized for ethylene polymerization. Silver catalysts have attracted less attention as the catalysts, but are potential for production of high molecular weight polyethylene. Herein, we report that silver complexes with various
N
-heterocyclic carbene (NHC) ligands in combination with modified methylaluminoxane (MMAO) afford polyethylene with high molecular weight (melting point over 140°C). SEM observation showed that the produced polyethylene has ultra-high molecular weight. NMR investigation of the reaction between the silver complexes with organoaluminums indicate that the NHC ligands transfer from the silver complex to aluminum to produce NHC aluminum complexes. Ph
3
C[B(C
6
F
5
)
4
] abstract methyl group from the NHC aluminum complex to afford cationic aluminum complex. The NHC aluminum complex promoted ethylene polymerization in the presence of Ph
3
C[B(C
6
F
5
)
4
] and organoaluminums. NHC ligand also promoted ethylene polymerization in combination with MMAO to produce polyethylene with high melting point (140.7°C). Thus, the aluminum complexes are considered to be the actual active species in silver-catalyzed ethylene polymerization.
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