Studies On Propylene/ethylene/conjugated Alkenes Polymerization Catalyzed By Half-sandwich Scandium Complexes

Over the past few decades,due to their special electronic property and stable valence,rare earth-based complexes have good performances in coordination polymerization of olefins(such as,a-olefin,conjugated alkenes).By tuning the structure of complexes,the controlled polymerization of conjugated alkenes(such as,styrene,isoprene)could be efficiently achieved.However,due to the strong chain transfer reactions(such’ as β-H,-CH3 eliminations),the controllable polymerization of propylene is a still difficult and challenging problem for the rare earth-based complexes.Besides,the copolymerization of a-olefins with conjugated alkenes(such as,styrene,1,3-butadiene and isoprene)have aroused great interests because of the novel structures,physical and chemical properties of their copolymers.The copolymerization of ethylene with conjugated alkenes have been successfully achieved.However,for the high efficient and controllable copolymerization of propylene with conjugated alkenes could not be achieved for now.Accordingly,in this thesis,by tuning the complexes’ steric and electronic property,the effects of complex structures on propylene polymerization were investigated systematically.The chain transfer polymerization and living polymerization of propylene were successfully achieved in high efficient way.Besides,the co(ter)polymerization of propylene with ethylene,styrene or isoprene were also investigated,giving series of co(ter)polymers with novel structures and controlled compositions.The main results were summarized as following:(1)A series of half-sandwich scandium dialkyl complexes bearing different alkyl ligand,Lewis base ligand as well as metallocene ligand,were synthesized to study the effects of complex structure on propylene polymerization.With Me3SiCH2 and THF ligand in combination,complexes LSc(CH2SiMe3)2(THF)(5a:L = C5Me4SiMe3;6:L = 1,3-(Me3Si)2C9H5)could serve as efficient catalysts for the chain transfer polymerization of propylene in high activity(105～106 g molSc-1 h-1),giving atactic polypropylene with low molecular weight(Mn～2 ×104 g/mol,Mw/Mn～2.00).With Me3SiCH2 and NHC ligand in combination,the β-H chain transfer reactions were completely suppressed by complex[1,3-(Me3Si)2C9H5]Sc(CH2SiMe3)2(ImiPr2)(8)at-30 0C,and living polymerization of propylene and ethylene was successfully achieved in high activity(106 g molSc-1 h-1),giving polypropylene and linear polyethylene with ultra-high molecular weight and narrow molecular weight distribution(Mn>106 g/mol,Mw/Mn～1.20).According to the in-situ 1H-NMR analysis and DFT calculations,the electronic positivity of Sc center was decreased by the stronger Lewis base ligand-NHC,which could explain the living polymerization of propylene with complex 8.(2)By tuning the complex’s structures,the multi-block copolymerization of propylene with styrene were successfully achieved by THF-containing half-sandwich scandium complexes in high activity(104～105 g molSc-1 h-1),while the copolymer compositions could be controlled by feed ratios.Besides,by tuning the complex’s structures,the terpolymerization of propylene with ethylene as well as styrene were also successfully achieved in high activity(105 g molSc-1 h-1),giving a series of propylene-ethylene-styrene terpolymers with controllable composition.For complex 5a,random terpolymers could be obtained.Meanwhile,for complex 6,the sPS-b-P(P-co-E)multi-block terpolymers were obtained in the whole composition range while the P-E blocks contained low S contents.The tensile properties of the terpolymers suggested that the terpolymer(S/E/P = 44/46/10)exhibited the characteristic thermoplastic elastomers.(3)By tuning the complex’s structures,propylene/isoprene copolymerization could be successfully achieved by THF-containing half-sandwich scandium complexes in high activity(104～105 g molSc-1 h-1),while the copolymer compositions could be controlled by feed ratios.The random copolymers were obtained by complex 5a,while the multi-block copolymers were obtained by complex 6.Besides,by tuning the complex’s structures,the terpolymerization of propylene with ethylene as well as isoprene were also successfully achieved in high activity(105 g molSc-1 h-1).The crystalline terpolymers with high ethylene contents could be obtained by complex 5a,while the propylene units and isoprene units were isolately distributed in the polyethylene backbone.The non-crystalline random terpolymers with much broader compositions could be obtained by complex 6.The epoxidized or hydroxylated/chlorinated ethylene/propylene copolymer with saturated backbones and double bonds on side chains were successfully obtained by the methods of epoxidation and ring-opening reactions.