Zhengguo Cai

Precision Chain-Walking Polymerization of trans-4-Octene Catalyzed by α-Diimine Nickel(II) Catalysts Bearing ortho-sec-Phenethyl Groups

α-Diimine nickel complexes bearing bulky ortho-sec-phenethyl groups (bis{[N,N-(4-methyl-2,6-di-sec-phenethylphenyl)imino]-1,2-dimethylethane}dibromonickel (1), bis{[N,N-(4,6-dimethyl-2-sec-phenethylphenyl)imino]-1,2-dimethylethane}dibromonickel (2), bis{[N,N-(4-methyl-2-sec-phenethylphenyl)imino]-1,2-dimethylethane}dibromonickel (3)) and {bis[N,N-(2,4,6-trimethylphenyl)imino]-1,2-dimethylethane}dibromidonickel (4) are used as a precatalyst for the polymerization of trans-4-octene upon activation with modified methylaluminoxane. These catalysts conduct chain-walking polymerization of trans-4-octene to give polymers possessing propyl and butyl branches with high molecular weight and narrow molecular weight distribution. The branching structure depends on the nickel complex as well as the polymerization temperature, and the ratio of propyl branch was increased with increasing the bulkiness of the ligand and decreasing the polymerization temperature. Consequently, the most bulky 1 among the complexes used is found to polymerize trans-4-octene with high 1,5-regioselectivity at -20 °C to give poly(1-propylpentan-1,5-diyl).

Precise synthesis of olefin block copolymers using a syndiospecific living polymerization system

This feature article summarizes the synthesis of novel olefin block copolymers using fast syndiospecific living homo- and copolymerization of propylene, higher 1-alkene, and norbornene with ansa-fluorenylamidodimethyltitaniumbased catalyst according to the authors’ recent results. The catalytic synthesis of monodisperse polyolefin and olefin block copolymer was also described using this living system.

Facile Synthesis of Novel Polyethylene-Based A-B-C Block Copolymers Containing Poly(methyl methacrylate) Using a Living Polymerization System

Ethylene-propylene-methyl methacrylate (MMA) and ethylene-hexene-MMA A-B-C block copolymers with high molecular weight (>100,000) are synthesized using fluorenylamide-ligated titanium complex activated by modified methylaluminoxane and 2,6-di-tert-butyl-4-methylphenol for the first time. After diblock copolymerization of olefin is conducted completely, MMA is added and activated by aluminum Lewis acid to promote anionic polymerization. The length of polyolefin and poly (methyl methacrylate) (PMMA) is controllable precisely by the change of the additive amount of olefin and polymerization time, respectively. A soft amorphous polypropylene or polyhexene segment is located between two hard segments of semicrystalline polyethylene and glassy PMMA blocks.

Synthesis of Hydroxy‐Functionalized Cyclic Olefin Copolymer and Its Block Copolymers with Semicrystalline Polyolefin Segments

Synthesis of hydroxy-functionalized cyclic olefin copolymer (COC) is achieved with remarkably high activity (up to 5.96 × 107 g-polymer mol-Ti-1 h-1 ) and controlled hydroxy group in a wide range (≈17.1 mol%) by using ansa-dimethylsilylene (fluorenyl)(amido)titanium complex. The catalyst also promotes living/controlled copolymerization to afford novel diblock copolymers consisting of hydroxy-functionalized COC and semicrystalline polyolefin sequence such as polyethylene and syndiotactic polypropylene, where the glass transition temperature of the norbornene/10-undecen-1-ol segment and each block length are controlled by comonomer composition and copolymerization time, respectively.

Synthesis of Hydroxy-functionalized Ultrahigh Molecular Weight Polyethylene Using Fluorenylamidotitanium Complex

Copolymerizations of ethylene and 1-dodecene were conducted with a series of ansa-fluorenylamidodimethyltitanium complexes, [t-BuNSiMe2Flu]TiMe2 (1a), [t-BuNSiMe2(2,7-tBu2Flu)]TiMe2 (1b), and [(1-adamantyl)NSiMe2(2,7-tBu2Flu)]TiMe2 (1c) activated by modified methylaluminoxane. The activity increased by the introduction of the alkyl groups on the fluorenyl and amido ligands, and 1c produced the highest molecular weight copolymers. Complex 1c also promoted copolymerization of ethylene and iBu3Al protected 10-undecen-1-ol with high activity (~2000 kg·mol−1·h−1), affording hydroxy-functionalized ultrahigh molecular weight polyethylene. The hydroxy content of the copolymers obtained was controllable by changing comonomer feed ratio. The introduction of a small amount of hydroxy group can alter the surface properties of polyethylene.

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.