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.
Efficient control of ethylene–norbornene copolymerization behavior of a fluorenylamido-ligated titanium complex: substituent effects of the amido ligand and copolymer properties
Copolymerization behavior is the most critical factor in the properties of polymeric materials. Highly active copolymerization of ethylene and norbornene was explored using (fluorenyl)(amido)titanium complexes bearing substituted amido ligands. The norbornene content and norbornene sequence distribution of the copolymers were controllable by changing the comonomer feed ratio and the polymerization temperature, respectively. The evaluation of the monomer reactivity ratios indicated that the copolymerization behavior of the (fluorenyl)(amido)titanium complex was tunable from alternating to random nature. The thermal and mechanical properties of the resulting copolymers depended on the sequence distribution of norbornene.
THE IRON-ACETOCARMINE METHOD OF FIXING AND STAINING CHROMOSOMES
A short description of this procedure was given in Vol. 55 of the American Naturalist, pp. 573â€”574. The method has now been used almost daily for five years, and certain improvements have suggested themselves. The solution can be prepared by mixing about equal volumes of glacial acetic acid and water. To this is added powdered carmine in excess. The liquid is then â€ ? just brought to boil, cooled, and decanted. To the red solution there are then added a few drops of a solution of ferric hydrate in 50 per cent. acetic acid, to act as a mordant. The amount of iron varies with different objects. Too much produces a precipitate in a short time. The more