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.
Regioselective living polymerization of allylcyclohexane and precise synthesis of hydrocarbon block copolymers with cyclic units
Precise control over macromolecular structures is a central goal and remains a great challenge in synthetic polymer chemistry. We report herein the living isomerization polymerization of allycyclohexane (ACH) using α-diimine nickel catalysts with high regioselectivity. The influences of catalyst structure, cocatalyst, and temperature on ACH polymerization were studied in detail. The macromolecular structure of polyallycyclohexanes (PACHs) was precisely controlled by living polymerization in combination with high regioselectivity under optimized conditions. A mechanistic model involving the 2,1-insertion selectivity of ACH and chain walking was proposed. Well-defined polyallycyclohexane-b-poly(1-hexene) copolymers (PACH-b-PH) with cyclic units were synthesized by sequential monomer addition.
The Origins of Jewish Guilt: Psychological, Theological, and Cultural Perspectives
The idea that guilt and Judaism are closely interlinked has a long historical legacy. After discussing recent work on anthropology and emotion focusing on shame and guilt, we examine three theories purporting to account for this link: psychoanalytic, theological, and guilt as a cultural stereotype particularly the notion of the Jewish mother.