Homo- and Copolymerizations of Ethylene and Norbornene Using Bis(β-ketoamino) Titanium Catalysts Containing Pyrazolone Rings
A series of bis(β-ketoamino) titanium complexes containing pyrazolone rings (1–3) have been synthesized, characterized, and used as precursors for homo- and copolymerization of ethylene and norbornene. The titanium complexes activated with methylaluminoxane (MAO) exhibited good activities for homopolymerization of ethylene (E) to produce linear polyethylenes (PEs). Ethylene–norbornene copolymers (E–N) were also prepared by these catalysts with moderate activities, and influences of ligand substituents and norbornene addition on copolymer microstructure were studied in detail. Microstructure analysis of the E–N copolymers by 13C NMR and differential scanning calorimetry (DSC) techniques showed that alternating (ENEN) and isolated (ENEE) norbornene predominately appeared in the copolymer chain, and the NN dyad and NNN triad sequences were also present in the copolymers obtained by the less bulky catalyst 1.
Living isomerization polymerizations of alkenylcyclohexane with camphyl α-diimine nickel catalysts
Abstract The steric effect of the α-diimine nickel catalyst on allylcyclohexane (ACH) and vinylcyclohexane (VCH) polymerizations has been studied with the aim of improving the monomer conversion and living fashion. We herein proposed a promising approach to enhancement on α-diimine nickel-catalyzed alkenylcyclohexane polymerization by moving steric bulk from the ortho-aryl to the ligand backbone to overcome the steric repulsion between them. A camphyl derived α-diimine nickel catalyst with 2,6-dimethylphenyl was successfully used to catalyze living isomerization polymerizations of ACH and VCH. Microstructure analysis of the obtained polymers revealed that ACH and VCH were preferentially inserted into secondary Ni–alkyl species (Ni–CH) in 2,1-insertion fashion followed by precise chain walking to form 1,ω-unit on the main chain. The isolated 1,2-insertion of the alkenylcyclohexane monomers infrequently took place, thus leading to the presence of 2,ω-unit by chain walking and 1,2-unit by direct insertion on the main chain.
Homo- and copolymerisation of norbornene and styrene with nickel bis(acetyl acetonate)/methylaluminoxane system
Abstract The homo and copolymerisations of norbornene and styrene with nickel bis(acetyl acetonate)/methylaluminoxane system were systematically investigated. This catalytic system shows a high activity towards homopolymerisation of both norbornene and styrene. For random copolymerisation, an increase in the initial styrene feed content leads to a gradual loss of activity relative to norbornene homopolymerisation. On the other hand, a drastic loss of activity, relative to styrene homopolymerisation, was found for very low norbornene feed contents. These results are qualitatively interpreted using the trigger coordination mechanism proposed by Ystenes. The structural characterisation of the polymers showed that norbornene polymerisation occurs via a 2,3 addition mechanism and that true copolymers are formed by random copolymerisation. At low styrene feed contents, only isolated styrene units or very short styrene sequences are present in the resulting copolymer. At higher styrene feed contents, short polystyrene sequences with more than eight styrene units may be formed. Determination of the reactivity ratios shows a much higher reactivity for norbornene (rnorbornene=17.8 and rstyrene=0.16). Size exclusion chromatography measurements have shown that polynorbornenes possess high molecular weights. Relatively low molecular weights were observed for homopolystyrene and copolymers.