Abstract
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.
Highlights
Cyclic olefin copolymers (COCs) of ethylene (E) with cyclic olefins, especially norbornene (N), representing a new class of amorphous materials has attracted great interest over the past decade because of their remarkable properties, such as high vapor and thermal resistance, excellent optical transparency, and high refractive indexes [1,2,3,4,5]. These material properties can be precisely controlled by varying monomer composition, sequence distribution, and the chain stereoregularity, which closely depends on the employed catalyst structure
Both the ligand environment and the center metal atom type play a major role in the copolymerization of ethylene and norbornene
The influences of catalyst structure and norbornene addition on copolymerization activity and incorporation of norbornene in copolymers have been investigated in detail
Summary
Cyclic olefin copolymers (COCs) of ethylene (E) with cyclic olefins, especially norbornene (N), representing a new class of amorphous materials has attracted great interest over the past decade because of their remarkable properties, such as high vapor and thermal resistance, excellent optical transparency, and high refractive indexes [1,2,3,4,5]. Non-metallocene titanium catalysts usually produce alternating E–N copolymers, the bis(α-alkyloxoimine) titanium catalyst facilitates random copolymers with high norbornene incorporation up to 76 mol %, because the electron-negative alkoxide group makes the titanium center prone to be attacks by the norbornene monomer [27]. These differences of the E–N copolymer microstructure highlight the powerful ligand influence on the reactivity of titanium catalysts and the potential reward for continued efforts to uncover new type of ligands and catalysts. The influences of catalyst structure and norbornene addition on copolymerization activity and incorporation of norbornene in copolymers have been investigated in detail
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