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2 results on '"polar olefin"'

1. The contradictory effect of the methoxy-substituent in palladium-catalyzed ethylene/methyl acrylate cooligomerization

Author

Paolo Fornasiero, Tiziano Montini, Barbara Milani, Angelo Meduri, Vera Rosar, Ennio Zangrando, Rosar, V., Meduri, A., Montini, T., Fornasiero, P., Zangrando, E., and Milani, B.

Subjects
Substituent, chemistry.chemical_element, homogeneous catalysi, 010402 general chemistry, 01 natural sciences, Medicinal chemistry, Inorganic Chemistry, chemistry.chemical_compound, ethylene/methyl acrylate copolymerization, Methyl acrylate, nitrogen-donor ligands, 010405 organic chemistry, Aryl, Cationic polymerization, palladium, homogeneous catalysis, coligomerization, 0104 chemical sciences, chemistry, polar olefin, Stereoselectivity, Cis–trans isomerism, Palladium, Methyl group
Abstract

Two new nonsymmetric bis(aryl-imino)acenaphthene ligands (Ar,Ar′-BIAN) and one symmetric Ar2-BIAN were studied. The three ligands share the presence of at least one methoxy group on one of the two aryl rings. These ligands were used for the synthesis of neutral and monocationic palladium(II) complexes of general formula [Pd(CH3)Cl(N–N)] and [Pd(CH3)(L)(N–N)][PF6] (N–N = Ar,Ar′-BIAN, Ar2-BIAN; L = CH3CN, dmso). Due to the nonsymmetric nature of the ligands and their coordination to palladium in a nonsymmetric chemical environment, cis and trans isomers are possible for the three series of complexes with Ar,Ar′-BIANs. Both a detailed NMR investigation in solution and the X-ray characterization in the solid state point out that the trans isomer is the preferred species for the neutral derivatives, whereas for the cationic compounds a decrease in the stereoselectivity of the coordination is observed. One of the new Ar,Ar′-BIANs differs from an already reported nonsymmetric α-diimine for the replacement, on one aryl ring, of a methyl group with a methoxy substituent, thus allowing a comparison of the structural features of the relevant complexes. The monocationic complexes were tested as precatalysts for the ethylene/methyl acrylate copolymerization under mild reaction conditions. Despite the structural similarities observed in solution with the already known precatalysts, the present compounds demonstrated a remarkable decrease in the productivity values associated with a higher affinity for the polar monomer.

Published
2018

2. Copolymerization of ethylene and halogenated styrenes using scandium catalysts.

Author

Zhang, Kai, Dou, Yanli, Zhang, Zhen, Jiang, Yang, Li, Shihui, and Cui, Dongmei

Subjects
*SCANDIUM catalysts, *COPOLYMERIZATION, *STYRENE, *GLASS transition temperature, *ETHYLENE, *FLUOROPOLYMERS
Abstract

Copolymerization of ethylene (E) and halogenated styrenes is screened by half-sandwich scandium catalyst 1 and constrained geometry scandium catalysts 2 – 4. The methyl-substituted N -heterocyclic carbene fluorenyl catalyst 3 initiates the E copolymerization with para -fluorostyrene (p FSt), para -chlorostyrene (p ClSt) and para -bromostyrene (p BrSt) to pseudo -random copolymers with an incorporation level of up to 46.3 mol%, 45.1 mol% and 37.5 mol%, respectively. Increasing reaction temperatures from 20 to 60 °C results in an increment of E/ p FSt copolymerization activity from 5.64 × 105 to 8.10 × 105 g mol Sc −1h−1. In contrast, a higher temperature dramatically depresses the E/ p ClSt copolymerization (4.86 × 105 g mol Sc −1h−1 at 20 °C vs 0.90 × 105 g mol Sc −1h−1 at 60 °C). At 20 °C, the E/ p BrSt copolymerization only affords a little pure polyethylene, and the E- p BrSt copolymer with 37.5 mol% p BrSt is obtained at 0 °C. The pseudo -random copolymers of E and halogenated styrenes give one glass transition temperature and decomposition temperature on DSC and TGA curves. Image 1 • Pseudo-random ethylene-halogenated styrene copolymers are synthesized using constrained geometry scandium catalysts. • A positive comonomer effect is found in ethylene copolymerization with halogenated styrenes. • The copolymerization activity is very sensitive to the reaction temperature. [ABSTRACT FROM AUTHOR]

Published
2020
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