| Polystyrene is a widely used synthetic material in manufacturing and daily life.However,the application of polystyrene is limited due to the absence of polar groups resulted from its non-polar characteristic.Incorporating polar groups or molecular chains into polystyrene can significantly improve its characteristics.Therefore,this study synthesized a series of functional styrene monomers with different substituent groups,and designed a series of rare earth metal complexes chelated with different ligands according to the structural characteristics of these monomers.The main research contents are summarized as follows:(1)One-pot reaction between pyridyl-methylene-cyclopentadienyl lithium salt,Ln Cl3and Li CH2Si Me3 afforded a series of constrained-geometry-configuration rare-earth metal bis(alkyl)complexes(Cp?CH2-Py)Ln(CH2Si Me3)2(THF)n(Py=C5H4N,Cp?=C5H4(Cp),Ln=Sc,n=0(1);Cp?=C9H6(Ind),Ln=Sc,n=0(2);Cp?=3-Me3Si-C9H5(3-Me3Si-Ind),Ln=Sc,n=0(3a),Ln=Lu(3b),Y(3c),n=1;Cp?=2,7-(tBu)2C13H8(2,7-(tBu)2-Flu),Ln=Sc(4a),n=0,Ln=Lu(4b),Y(4c),n=1).And the above complexes are characterized by NMR spectroscopy and single crystal X ray diffraction.Under the activation effect of[Ph3C][B(C6F5)4]and AliBu3,these complexes display different catalytic performances towards styrene polymerization.Rare-earth metal bis(alkyl)precursors bearing Cp,Ind and3-Me3Si-Ind segments exhibited very low catalytic activity for the polymerization of styrene.All electron-donating tBu substituted complexes 4a,4b and 4c showed very high activity and perfect syndiotactivity(rrrr>99%)for styrene polymerization.Gel chromatography(GPC)and differential scanning calorimetry(DSC)analysis of the polymer obtained from the catalytic system show that the polymer has relatively narrow molecular weight distribution(PDI=1.28-2.49),high molecular weight(54.1×104)and a significant melt peak at 270°C.(2)Coordination(co)polymerization of para-isopropenylstyrene(p IPSt)and meta-isopropenylstyrene(m IPSt)was initiated by scandium(Sc)based catalysts,leading to the formation a functional syndiotacity Polystyrene bearing pendant isopropenyl groups(rrrr>99%).Sc catalysts demonstrates overwhelmingly chemoselectivity towards the vinyl group over the isopropenyl group of isopropenylstyrene.Compared to the constrained geometry Sc catalysts having electron-donating pyridyl methylene fluorenyl ligands Flu?CH2Py(1,Flu?=C13H8;2,Flu?=2,7-tBu2C13H6,Py=C5H5N),the half-sandwich Sc catalysts containing electron-withdrawing substituents[3,C13H8Si Me3Sc(CH2Si Me3)2(THF);4,C5Me4Ph Sc(CH2C6H4NMe2-o)2]show much higher catalytic activity under identical conditions.The activity of 4 can be over 2164 kg mol Sc-1 h-1 at room temperature at a lower monomer concentration(1 mol/L).Moreover,copolymerization of p IPSt and styrene(St)proceeded fluently in a pathway close to ideal copolymerization,with close matched monomer reactivity ratios:rp IPSt=1.05,r St=0.83.Therefore,a series of statically random copolymers with pendant unsaturated olefinic groups,ranging from 5%to 90%,were accessed.These pendant isopropenyl groups could be readily converted into epoxide and bromide moieties at mild reaction conditions.(3)Styrene monomers with different alkynyl group substitutions,such as 4-(1-hexynyl)styrene(HES),4-(phenylethynyl)styrene(PES)and4-(trimethylsilyl)ethynylstyrene(TES),were designed and synthesized,and catalytic behavior of rare earth metal complexes(half-sandwich scandium precursor C5Me4Ph Sc(CH2C6H4NMe2-o)2(1)and constrained-geometry-configuration precursors C13H8CH2Py Sc(CH2Si Me3)2(2,Py=C5H4N),2,7-(tBu)2C13H8CH2Py Ln(CH2Si Me3)2(THF)n(Ln=Sc(3a),n=0;Y(3b),Lu(3c),n=1))on these three monomers was studied.Under mild conditions,perfect syndiotactic products(rrrr>99%)are produced by homopolymerizations of HES,PES and TES.The random copolymerizations of TES and styrene(St)proceed fluently by precursor 3b,and the insertion fractions of TES are tuned in a range of 0 to 100 mol%via changing the TES-to-St feed ratio.The trimethylsilyl groups are facilely eliminated from the TES-based polymers by tetrabutylammonium fluoride to give terminal ethynyl-containing polystyrenes,the reactions of which with azide compound,carbon dioxide and anthracene-9-aldehyde afford a series of functional syndiotactic polystyrenes.(4)The catalytic performance of rare-earth metal dialkyl complexes in combination with DMAO(dry methylaluminoxane)was explored.In the presence of 60 equivalents of DMAO,the half-sandwich complex(C13H8CH2Ph)Sc(CH2Si Me3)2(THF)(1)is inert for styrene polymerization,but(C5Me4Ph)Sc(CH2C6H4NMe2-o)2(2)converts 18%styrene into syndiotactic polystyrene.Under the same conditions,the constrained-geometry configuration sandium complex(C13H8CH2Py)Sc(CH2Si Me3)2(3a)displays extremely high catalytic activity(>6420 kg?mol Sc-1 h-1)and perfect syndiospecific(rrrr>99%)for styrene polymerization,and,in contrast,its lutetium(3b)and yttrium(3c)analogues are nearly inactive.Although the binary catalytic system 3a/DMAO exhibits very low activity for 4-methoxystyrene polymerization,it is an efficient catalyst for the syndioselective polymerization of other styrene derivatives such as 2-methoxystyrene,4-methylthiostyrene,4-fluorostyrene,4-dimethylhydrosilylstyrene,alkyne-susbstituted styrenes and 4-methylstyrene.In addition,the binary system 3a/DMAO can copolymerize ethylene and styrene to give alternating copolymers with a single glass transition at 80°C and 4 bar ethylene pressures.(5)Coordination copolymerization of ethylene(E)with polar vinyl monomers is the most direct and challenging approach to preparing functional polyolefins.The main obstacle to this process is that the Lewis acid-base interaction between polar group and transition metal significantly depresses the catalytic activity.Herein,we present the synthesis and characterization of two binuclear half-sandwich scandium complexes C1-Sc2 and C2-Sc2bridged with-CH2-and-CH2CH2-linker,respectively.In the copolymerization of E and para-methoxystyrene(p MOS),C1-Sc2 and C2-Sc2 exhibit 13 and 7 times greater polymerization activities,respectively,than does their mononuclear analogue Sc1.The excellent catalytic performance is extended to polar olefins bearing varied linker lengths and polar groups,where binuclear catalysts display higher catalytic activity and improved tolerance towards polar group versus mononuclear analogue.Mechanistic elucidation by DFT simulation suggests that the synergic action of two active species plays a key role in promoting the copolymerization of E and polar monomer. |
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