Ceria based catalysts are very effective for the synthesis of cyclic carbonate such as ethylene carbonate (EC) and propylene carbonate (PC) by the reaction of CO 2 with ethylene glycol and propylene glycol. In these reactions, polycarbonate and ethers (diethylene glycol and dipropylene glycol) were not detected under optimum reaction conditions. This indicates that the PC and EC formation over CeO 2 -ZrO 2 catalysts is highly selective. Catalytic activity was much dependent on the composition and calcination temperature of catalysts. On the basis of catalyst characterization by means of surface area measurement, X-ray diffraction, thermogravimetric analysis, and temperature programmed desorption of NH 3 and CO 2 , the relations between catalytic performance and properties are discussed.
Coordination-insertion copolymerization of ethylene with 1,1-disubstituted ethylenes bearing a polar functional group, such as methyl methacrylate (MMA), is a long-standing challenge in catalytic polymerization. The major obstacle for this process is the huge difference in reactivity of ethylene versus 1,1-disubstituted ethylenes toward both coordination and insertion. Herein we report the copolymerization of ethylene and 1,1-disubstituted ethylenes by using an imidazo[1,5-a]quinolin-9-olate-1-ylidene-supported palladium catalyst. Various types of 1,1-disubstituted ethylenes were successfully incorporated into the polyethylene chain. In-depth characterization of the obtained copolymers and mechanistic inferences drawn from stoichiometric reactions of alkylpalladium complexes with methyl methacrylate and ethylene indicate that the copolymerization proceeds by the same coordination-insertion mechanism that has been postulated for ethylene.
A series of palladium complexes bearing a bisphosphine monoxide with a methylene linker, that is, [κ 2 -(Pd/ BPMO), were synthesized and evaluated as catalysts for the homopolymerization of ethylene and the copolymerization of ethylene and polar monomers. X-ray crystallographic analyses revealed that these Pd/BPMO complexes exhibit significantly narrower bite angles and longer Pd−O bonds than Pd/BPMO complexes bearing a phenylene linker, while maintaining almost constant Pd−P bond lengths. Among the complexes synthesized, menthyl-substituted complex 3f (R 1 = (1R,2S,5R)-2-isopropyl-5-methylcyclohexan-1-yl; R 2 = Me) showed the best catalytic performance in the homo-and copolymerization in terms of molecular weight and polymerization activity. Meanwhile, complex 3e (R 1 = t-Bu; R 2 = Me) exhibited a markedly higher incorporation of comonomers in the copolymerization of ethylene and allyl acetate (≤12.0 mol %) or methyl methacrylate (≤0.6 mol %). The catalytic system represents one of the first examples of late-transition-metal complexes bearing an alkylene-bridged bidentate ligand that afford high-molecular-weight copolymers from the copolymerization of ethylene and polar monomers.
Nickel
complexes bearing bidentate alkylphophine–phenolate
ligands were synthesized and applied to the polymerization of propylene
and the copolymerization of propylene and polar monomers. Therein,
the use of bulky alkyl substituents on the phosphorus atom was crucial
for the formation of highly regioregular polypropylenes. Theoretical
calculations suggested that the 1,2-insertion of propylene is favored
over the 2,1-insertion in these nickel-catalyzed (co)polymerization
reactions. The substituent at the ortho position
relative to the oxido group greatly influences the polymerization
activity, the molecular weight, and stereoregularity of the polypropylenes.
This method delivers moderately isotactic ([mm] ≤
68%) crystalline polypropylenes. The present system represents the
first example for a nickel-catalyzed regiocontrolled copolymerization
of propylene and polar monomers such as but-3-en-1-ol, but-3-en-1-yl
acetate, and tert-butyl allylcarbamate.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.