Ethylene And Styrene Polymerization Catalyzed By The ?-diketomine Binuclear Titanium Complexes

Polyolefin industry is developing rapidly in China.With the overcapacity of low-grade products in the industry,the development and production of high-grade polyolefin products are urgently needed.The catalyst plays a decisive role in the performance of polyolefin.We prepared a series of?-diketomine tridentate binuclear titanium complexes Ti²L₁-Ti²L₄ with the advantages of open coordination environment of?-diketomine tridentate titanium complexes and the synergistic effect of bimetallic titanium complexes,and studied their catalytic properties towards olefin polymerization,which main contents are as follows:1.A series of bis-?-diketomine tridentate ligands and corresponding binuclear titanium complexes Ti²L₁-Ti²L₄ have been prepared and characterized by ¹H NMR,¹³C NMR and FT IR.The?-diketomine tridentate binuclear titanium complexes can catalyze ethylene polymerization with high activity over 10⁶ g/?mol.Ti.h.atm?with the activation of MMAO.The structure of the catalysts greatly affected the catalytic performances.With the increase of chain length and size of substituents in alkylthiol side arm,the polymerization activity of the series of catalysts decreased obviously along with the molecular weight of the obtained polymer increased.The polymers produced by the binuclear titanium complexes except Ti²L₂owned narrow molecular weight distribution of about 3,which is similar with that by mononuclear complexes and indicated that these binuclear titanium complexes possessed symmetric structure and contained single-site active species.2.The performances of ethylene copolymerization with?-olefin,norbornene or polar monomer 9-decene-1-alcohol catalyzed by?-diketomine tridentate binuclear titanium complexes were studied.With the activation of MMAO,the tridentate binuclear titanium complexes exihibited high activity up to 10⁶ g/?mol.Ti.h.atm?and obvious positive comonomer effect for ethylene/1-hexene copolymerization,that is,the catalytic activity increased with the increase of 1-hexene feeds,and the highest activity can reach twice more than that of the ethylene homopolymerization.The copolymerization activity and the comonomer incorporation ratio obtained by these binuclear titanium complexes decreased gradually with the substituents in alkylthiol side arm changing from methyl to propyl and octy.Furthermore,compared with the mononuclear titanium analogue,the binuclear titanium complexes produced copolymer with higher comonomer incorporation,indicating that there exists the synergistic effect of bimetallic titanium complexes.The binuclear titanium complexes can also catalyze the copolymerization of ethylene and norbornene or 9-decene-1-alcohol with high activity,showing that the binuclear titanium complexes had a certain tolerance to the comonomer with large hindrance and polar group.The alkyl groups on the sulfur side arm had great influences on the copolymerization of ethylene and norbornene,but little influences for the copolymerization of ethylene with 9-decene-1-alcohol,showing that the copolymerization of ethylene and norbornene is affected by steric hindrance effect,while the copolymerization of ethylene and 9-decene-1-alcohol is mainly affected by the electronic effects of complexes.3.The behaviors of styrene solution polymerization and bulk polymerization catalyzed by binuclear titanium complexes were investigated.The obtained polymers were syndiotactic polystyrenes with syndiotacticity nearly 100%.The activity of styrene bulk polymerization is obviously higher than that of solution polymerization,but the syndiotacticity of obtained polymer is slightly reduced with still more than 98%.With the increase of temperature,the activity of bulk polymerization gradually increased along with the decrease of the melting point and intermodulation of the polymer,which may be due to the increase of the insertion rate of styrene into the active center with the increase of temperature and the ability to control the tacticity of the active center decrease,along with the faster chain transfer and free radical polymerization of the styrene.Compared with the mononuclear titanium analogue,the binuclear titanium complexes catalyze the bulk polymerization of styrene with higher catalytic activity,and the obtained polymers have higher syndiotacticity.