Controlled Coordination (Co) Polymerization Of Olefin And Conjugated Diene Catalyzed By Rare-earth Complexes

Elastomer synthesized by commercial monomers such as ethylene,styrene,butadiene,isoprene has low cost,excellent performance and good compatibility with other polyolefin,and was widely used in industrial field and daily life.At present the capacity of low-end products is excess for market demands in China’s polyolefin-based elastomer industry,while high-value-added production largely relies on imports.So,it is necessary to develop elastomers with new microstructures and properties to promote competitiveness of elastomer manufacturing and meet demands of our country.Herein,using rare-earth metal complexes,coordination(co)polymerization of olefins and conjugated dienes were realized and regioselectivity,composition and sequence distribution of copolymers were precisely adjusted,affording a series of new elastomers with potential applications.Representative results are listed as follows:(1)Random copolymerization of butadiene and isoprene was achieved using PNP-pincer carbazolide yttrium complex 1[3,6-(’Bu)2-1,8-(PPh2)2-carbazole]Y[CH2C6H4N(Me)2-o]3.By adjusting polymerization conditions,a series of high cis-1,4-regulated(cis-1,4>99 mol%)butadiene-isoprene rubber(CBIR)with isoprene content varying in the range of 11～53 mol%(CBIR-1～5)were prepared.Copolymers with lower molecular weights(12.1 × 104 g/mol and 19.0 × 104 g/mol)with 20 mol%isoprene content(CBIR-6,7)were also prepared.Only as low as 11 mol%isoprene incorporation,the crystallization of CBIR could be completely suppressed,but still has a low glass-transition temperature(Tg=-86.4℃).Containing 20%isoprene content,CBIR-7 is the most suitable for processing,and its vulcanizate exhibits the highest tensile strength(17.6 MPa)and elongation at break(610%),meanwhile it still maintains good low-temperature resistance by possessing a low Tg=-82.1℃.(2)Coordination polymerization of a series reactive monomers 2-(R-Ph)-1,3-butadienes(A:R=4-Me-,B:3-Me-,C:2-Me-,D:H-,E:4-Pentyl-,F:4-F-;G:4-Cl-,H:4-Br-)using N-heterocyclic carbene functionalized fluorenyl lutetium complex 2(Flu-NHC)Lu(CH2SiMe3)2(Flu-NHC=C13H8CH2CH2(NCHCCHN)C6H2Me3-2,4,6),lutetium bis(alkyl)complex bearing NPN-bidentate ligand 3[Ph2P(NC6H3iPre-2,6)(NC6H4iPr2-6)]Lu(CH2SiMe3)2THF and yttrium bis(alkyl)complex 4[Ph2P(NC6H3iPr2-2,6)(NC6H4iPr2-6)]Y(CH2SiMe3)2THF.Catalyst 2 exhibited low selectivity(3,4-=65.2 mol%)for polymerization of A,while 3 and 4 could produce conjugated diene polymers with 98.1 mol%3,4-regularity and perfect(>99 mol%)3,4-regularity,respectively.The resultant polymers have low PDIs(<1.1).Catalyst 4 exhibited high 3,4-selectivity(>99 mol%)for the polymerizations of other monomers except C,which indicated that activity didn’t impaired by the polar group but the ortho-substituted group on phenyl group but diminished largely by the steric hindrance of the ortho-methyl substituent.Due to the highly regulated microstructures and rigid phenyl substituents,the resultant reactive polymers have high glass transition temperatures(46.3～71.5℃),which were to transferred into a series of plastic materials with highly dense hydroxyl side chains,mediated by the hydroboration/oxidation reactions(3)Using a series of newly designed quinolinyl-functionalized cyclopentadienyl and thiophene-fused cyclopentadienyl scandium complexes 5[1-(8-quinolinyl)-3,4-Me2-cyclopentadiene]Sc(CH2SiMe3)2,6[1-(8-quinolinyl)-2,3,4,5-Me4-cyclopentadiene]Sc(CH2SiMe3)2,and 7[2,4,5-Me3-6-(8-quinolinyl)-cyclopenta[b]thiophene]Sc(CH2SiMe3)2,polymerization of 2,3-dimethyl-1,3-butadiene(DMB)and copolymerization of E and DMB were carried out.Three catalysts exhibit high trans-1,4-selectivity(97.6 mol%)for DMB homopolymerization.Based on these results,the copolymerization of DMB and ethylene(E)was realized with high activity show the rare comonomer "positive effect".More interestingly,high 1,2-regioselectivity of DMB was achieved(96.6 mol%)in its copolymerization with ethylene.DFT calculation revealed that the regioselectivity switch is triggered by the comonomer E,which coordinates to the active metal center to cause the isomerization of the active species from the Sc-η3-allyl mode to the Sc-σ-alkyl mode.The resultant E/DMB copolymers bear the pseudo-random sequence distributions to exhibit high elongation and strength(595%,12.2 MPa)contrary to the crystalline properties of PDMB and PE precursors,indicating a rubbery material.(4)Using thiophene-fused cyclopentadienyl ligated scandium bis(alkyl)complexes 8(2,5-Me2-3-Ph-SiMe3-cyclopenta[b]thiophenyl)Sc(CH2SiMe3)2THF,high cis-1,4-copolymerization of BD and E was carried out and integrated plastic polyethylene(PE)sequences and elastic polybutadiene(PBD)into one molecular chain to fabricate novel "plastic-rubber".By adjusting polymerization conditions,random copolymers E/BD-1～5 with E content varying from 13 mol%to 50 mol%and the tapered E/BD-6 with 21 mol%ethylene content and the random copolymer with longer PE sequences E-BD-7 at the E content of 30 mol%could also be produced.The mechanical properties of random copolymers were enhanced as E content increasing,with 50 mol%E incorporation,the tensile strength of copolymer is 3.99 MPa,while elongation at break reaches to 450%,and tear strength is 20.3 kN/m.It is found that at the same E incorporation,E/BD copolymers with longer PE sequence and tapered structure have superior tensile properties but inferior tear strength.Morphology study revealed that more obvious microphase separation should be attributed to tha.As for E/BD vulcanizates,E incorporation lead to superior tensile properties(19.1 MPa,805%),tear strength(71.6 kN/m)and anti-aging properties than BR vulcanizates.(5)Using AliBu3 as chain transfer agent,rare-earth metal complex 9(Flu-CH2-Py)Sc(CH2SiMe3)2 catalyzed the copolymerization of ethylene and styrene to give the alternating sequence enriched copolymer with the chain transfer efficiency of 100%.Different catalytic system were screened to achieve chain shuttling polymerization.Complex 10[PhC(NC6H4iPr2-2,6)2]Y(CH2SiMe3)2THF was employed to catalyze the copolymerization of ethylene and styrene,but the chain transfer efficiency is less than 100%and failed to achieve chain shuttling polymerization.Complex 11(2,4,5,6-Me4-cyclopenta[b]thiophenyl)Sc(CH2SiMe3)2THF was found to catalyze the copolymerization of ethylene and styrene with the chain transfer efficiency of 100%.When the ratio of[AliBu3]0/[9+11]0<20,the ternary catalytic system 9,11 and AliBu3 could prepare multi-block copolymers containing alternating sequences and syndiotactic polystyrene sequences with unimodal molecular weight distributions,indicating the success of chain shuttling.The sequence distribution was effectively controlled by adjusting the ratio of 9 to 11.