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Dongmei Cui - One of the best experts on this subject based on the ideXlab platform.

  • highly syndiotactic Coordination co Polymerization of para methylselenostyrene
    Macromolecules, 2021
    Co-Authors: Yuanhao Zhong, Dongmei Cui
    Abstract:

    Synthesis of selenium-containing syndiotactic polystyrene through Coordination Polymerization is difficult to achieve since selenium atoms usually poison the applied catalysts. Herein, we report the Coordination Polymerization of para-methylselenostyrene (pMSS) and its coPolymerization with styrene (St) using pyridyl-methylene-fluorenyl-supported complexes [(Py–CH₂–Flu)Ln(CH₂SiMe₃)₂(THF)ₙ (Ln = Y (1), n = 1; Ln = Sc (2), n = 0)]. Complex 1 was completely inert, while complex 2 was highly active and exhibited >99% syndioselectivity to yield poly(pMSS) as the rare crystalline polymer-containing selenium atoms in side chains. In addition, the coPolymerization of polar pMSS with nonpolar St under various pMSS-to-St ratios proceeded smoothly. The excellent syndiotacticity was maintained in the coPolymerization, and the obtained copolymers have random sequence distributions confirmed by ¹³C NMR spectrum analysis and kinetics study. The optical performances of the copolymers with different incorporations of selenium were studied.

  • highly syndioselective Coordination co Polymerization of vinyl heteroaromatic monomers using rare earth metal complexes
    Polymer Chemistry, 2020
    Co-Authors: Dongmei Cui, Tiantian Wang
    Abstract:

    The Coordination Polymerization of polar vinyl monomers is a theoretical challenge since Lewis basic polar groups are usually poisonous to Lewis acidic transition-metal catalysts. In this work, we report the Coordination Polymerization of polar vinyl heteroaromatic monomers, including 2-vinylfuran (VF), 2-methyl-5-vinylfuran (MVF), 2-vinylbenzofuran (VBF), 2-vinylthiophine (VT), 2-vinylbenzothiophene (VBT) and 2-vinyldibenzothiophene (VDBT), by using the rare-earth-metal complexes 1–4 [(bis(2,6-dimethyl anilido)ketimine)Y(CH2SiMe3)2(THF) (1), (2,4,5,6-Me4-4H-cyclopenta[b]thiophenyl)Sc(CH2SiMe3)2(THF) (2), (Flu-CH2-Py)Sc(CH2SiMe3)2 (3) and (Flu-CH2-Py)Sc(CH2SiMe3)2(THF) (4)]. The Polymerizations of vinylfuran derivatives exhibited extremely low activity and gave crosslinked products. Strikingly, high stereo-selectivity Coordination Polymerization of VBT was achieved successfully with high activity by using complex 4. High-molecular-weight and perfect syndioselective (rrrr > 99%) poly(vinylbenzothiophene) (PVBT) was afforded. In addition, the coPolymerization of VBT and styrene (St) proceeded fluently in a wide range of VBT-to-St ratios. The competitive reactivity ratios of rVBT = 3.72 and rSt = 0.42 indicate the gradient sequence distribution of VBT-St copolymers. Moreover, the coPolymerization of St and vinyldibenzothiophene (VDBT) can also be realized to give highly thermally stable products, although the homoPolymerization of VDBT is rather sluggish due to the sterically hindered dibenzothiophenyl group.

  • syndioselective Coordination co Polymerization of alkyne substituted styrenes using rare earth metal catalysts
    Macromolecules, 2020
    Co-Authors: Dongtao Liu, Zhen Zhang, Yanli Dou, Zhongyi Cai, Dongmei Cui
    Abstract:

    Developing convenient methods to introduce functional groups into syndiotactic polystyrene has gained increasing attention in recent years. Herein, we report the Coordination Polymerization of 4-(1...

  • stereoselective Polymerization of an aromatic vinyl monomer to access highly syndiotactic poly vinyl alcohol
    Macromolecular Rapid Communications, 2020
    Co-Authors: Dongmei Cui, Jianming Huang, Yang Jiang, Zhen Zhang
    Abstract:

    Streoregular poly(vinyl alcohol) is hard to obtain because vinyl alcohol is unstable relative to its tautomer acetaldehyde, and the monomer precursor vinyl ester is poisonous to the Coordination catalyst. Herein, the Coordination Polymerization of 2-vinyl-2,1-borazanaphthalene (BN2VN) is reported by the linked or unlinked half-sandwich ligands attached scandium precursors ((FluSiMe3 )Sc(CH2 SiMe3 )2 (THF) (THF = tetrahydrofuran, 1), (FluCH2 CH2 -NHC-R)Sc(CH2 SiMe3 )2 (THF) (R = mesityl 2, i Pr 3, Me 4), and (FluCH2 Py)Sc(CH2 SiMe3 )2 (5) for the first time. Among these precursors, complex 5 converts 600 equivalents of BN2VN into polymer within 5 min to reach an activity as high as 8.99 × 105 g molSc-1 h-1 . The resultant products show excellent syndiotacticity and melting temperatures above 300 °C, which can be transferred to syndiotactic poly(vinyl alcohol) with 90% rr triad content by postPolymerization oxidation.

  • access to hydroxy functionalized polypropylene through Coordination Polymerization
    Angewandte Chemie, 2020
    Co-Authors: Yuanhao Zhong, Iskander Douair, Tiantian Wang, Laurent Maron, Dongmei Cui
    Abstract:

    Preparation of polyethylenes containing hydroxy groups has been already industrialized through radical coPolymerization under harsh conditions followed by alcoholysis. By contrast, hydroxy-functionalized polypropylene has proven a rather challenging goal in polymer science. Propylene can't be polymerized through a radical mechanism, and its Coordination coPolymerization with polar monomers is frustrated by catalyst poisoning. Herein, we report a new strategy to reach this target. The Coordination Polymerization of allenes by rare-earth-metal precursors affords pure 1,2-regulated polyallenes, which are facilely transformed into poly(allyl alcohol) analogues by subsequent hydroboration/oxidation. Strikingly, the coPolymerization of allenes and propylene gives unprecedented hydroxy-functionalized polypropylene after post-Polymerization modification. Mechanistic elucidation by DFT simulation suggests kinetic rather than thermodynamic control.

Eugene Y X Chen - One of the best experts on this subject based on the ideXlab platform.

  • Living Coordination Polymerization of a Six-Five Bicyclic Lactone to Produce Completely Recyclable Polyester
    Angewandte Chemie - International Edition, 2018
    Co-Authors: Jian-bo Zhu, Eugene Y X Chen
    Abstract:

    The development of chemically recyclable polymers promises a closed-loop approach towards a circular plastic economy but still faces challenges in structure/property diversity and dePolymerization selectivity. Here we report the first successful Coordination ring-opening Polymerization of 4,5-trans-cyclohexyl-fused γ-butyrolactone (M1) with lanthanide catalysts at room temperature, producing P(M1) with Mn up to 89 kg/mol, high thermal stability, and a linear or cyclic topology. The same catalyst also catalyses selective dePolymerization of P(M1) back to M1 exclusively at 120 °C. This Coordination Polymerization is also living, enabling the synthesis of well-defined block copolymer.

  • stereoregular brush polymers and graft copolymers by chiral zirconocene mediated Coordination Polymerization of p3ht macromers
    Polymers, 2017
    Co-Authors: Yang Wang, Miao Hong, Travis S Bailey, Eugene Y X Chen
    Abstract:

    Two poly(3-hexylthiophene) (P3HT) macromers containing a donor polymer with a polymerizable methacrylate (MA) end group, P3HT-CH2-MA and P3HT-(CH2)2-MA, have been synthesized, and P3HT-(CH2)2-MA has been successfully homopolymerized and copolymerized with methyl methacrylate (MMA) into stereoregular brush polymers and graft copolymers, respectively, using chiral ansa-zirconocene catalysts. Macromer P3HT-CH2-MA is too sterically hindered to polymerize by the current Zr catalysts, but macromer P3HT-(CH2)2-MA is readily polymerizable via either homoPolymerization or coPolymerization with MMA in a stereospecific fashion with both C2-ligated zirconocenium catalyst 1 and Cs-ligated zirconocenium catalyst 2. Thus, highly isotactic (with mm% ≥ 92%) and syndiotactic (with rr% ≥ 93%) brush polymers, it-PMA-g-P3HT and st-PMA-g-P3HT, as well as well-defined stereoregular graft copolymers with different grafted P3HT densities, it-P(M)MA-g-P3HT and st-P(M)MA-g-P3HT, have been synthesized using this controlled Coordination-addition Polymerization system under ambient conditions. These stereoregular brush polymers and graft copolymers exhibit both thermal (glass and melting) transitions with Tg and Tm values corresponding to transitions within the stereoregular P(M)MA and crystalline P3HT domains. Acceptor molecules such as C60 can be effectively encapsulated inside the helical cavity of st-P(M)MA-g-P3HT to form a unique supramolecular helical crystalline complex, thus offering a novel strategy to control the donor/acceptor solar cell domain morphology.

  • precision polymer synthesis via chemoselective stereoselective and living controlled Polymerization of polar divinyl monomers
    Synlett, 2017
    Co-Authors: Fernando Vidal, Eugene Y X Chen
    Abstract:

    Post-Polymerization modification of polymers carrying reactive side-chain groups has been a successful method to introduce target functionalities into polymer systems, based commonly on atactic amorphous polymers. Effective synthetic methods for obtaining stereoregular functional polymers from Polymerization of polar divinyl monomers must achieve not only high chemoselectivity and livingness of the Polymerization, but also high stereoregularity of the polymer main-chain backbone, preferably under ambient reaction conditions for a facile manipulation over the spatial orientation of such functional groups. In this account, we review some recent metal-mediated Coordination Polymerization systems that are simultaneously chemoselective, stereo­selective, and living/controlled for obtaining highly stereoregular and densely functionalized polymers. In addition, we compare such results with those obtained by certain organocatalysts and describe the efforts to post-functionalize the olefin-carrying stereoregular polymers with the efficient thiol-ene ‘click’ reaction. 1 Introduction 2 Metal-Catalyzed Coordination-Addition Polymerization of Polar Divinyl Monomers 3 Organocatalyzed Conjugate-Addition Polymerization of Polar Divinyl Monomers 4 Post-Functionalization of Vinyl-Containing Stereoregular Polymers 5 Conclusions and Outlook

  • robust cross linked stereocomplexes and c60 inclusion complexes of vinyl functionalized stereoregular polymers derived from chemo stereoselective Coordination Polymerization
    Journal of the American Chemical Society, 2016
    Co-Authors: Fernando Vidal, Laura Falivene, Lucia Caporaso, Luigi Cavallo, Eugene Y X Chen
    Abstract:

    The successful synthesis of highly syndiotactic polar vinyl polymers bearing the reactive pendant vinyl group on each repeat unit, which is enabled by perfectly chemoselective and highly syndiospecific Coordination Polymerization of divinyl polar monomers developed through this work, has allowed the construction of robust cross-linked supramolecular stereocomplexes and C60 inclusion complexes. The metal-mediated Coordination Polymerization of three representative polar divinyl monomers, including vinyl methacrylate (VMA), allyl methacrylate (AMA), and N,N-diallyl acrylamide (DAA) by Cs-ligated zirconocenium ester enolate catalysts under ambient conditions exhibits complete chemoselectivity and high stereoselectivity, thus producing the corresponding vinyl-functionalized polymers with high (92% rr) to quantitative (>99% rr) syndiotacticity. A combined experimental (synthetic, kinetic, and mechanistic) and theoretical (DFT) investigation has yielded a unimetallic, enantiomorphic-site-controlled propagation ...

  • chiral and achiral imino phenoxy based cationic group 4 non metallocene complexes as catalysts for Polymerization of renewable α methylene γ butyrolactones
    Dalton Transactions, 2013
    Co-Authors: Ravikumar R Gowda, Eugene Y X Chen
    Abstract:

    Protonolysis of M(Bn)4 (M = Zr, Ti; Bn = benzyl) with equimolar 2,4-di-tert-butyl-6-[(2,6-diisopropylphenylimino)methyl]phenol [(2,6-iPr2C6H3)NC(3,5-tBu2C6H2)OH] in toluene at −30 °C to 25 °C cleanly affords the corresponding achiral (imino)phenoxy-tribenzyl complexes, [(2,6-iPr2C6H3)NC(3,5-tBu2C6H2)O]Zr(Bn)3 (1) and [(2,6-iPr2C6H3)NC(3,5-tBu2C6H2)O]Ti(Bn)3 (2). A chiral dibenzyl complex 3 incorporating the unsymmetric, tetradentate amino(imino)bis(phenoxy) ligand, [2,4-Br2C6H2(O)(6-CH2(NC5H9))CH2NCH(2-adamantyl-4-MeC6H2O)]Zr(Bn)2 (3), has also been prepared using the same protonolysis protocol. Abstractive activation of 1 with B(C6F5)3·THF in CD2Cl2 at room temperature (RT) affords clean, quantitative formation of the corresponding zirconium cation [((2,6-iPr2C6H3)NC(3,5-tBu2C6H2)O)Zr(Bn)2(THF)]+[BnB(C6F5)3]− (4). Likewise, benzyl abstraction of 2 with B(C6F5)3·THF in CD2Cl2 at RT generates the cationic titanium complex [((2,6-iPr2C6H3)NC(3,5-tBu2C6H2)O)Ti(Bn)2(THF)]+[BnB(C6F5)3]− (5), accompanied by a small amount of decomposed species as a result of C6F5 transfer. The dibenzyl cations 4 and 5 have been characterized spectroscopically, and their structures have been confirmed by single crystal X-ray diffraction analysis. Characteristics of the Coordination Polymerization of renewable α-methylene-γ-butyrolactone monomers by the cationic catalysts derived from achiral complexes 1 and 2 as well as chiral complex 3 have been investigated, representing the first study of such Polymerization by non-metallocene catalysts.

Lawrence R Sita - One of the best experts on this subject based on the ideXlab platform.

  • electronic effect rate enhancement in the stereoselective living coordinative Polymerization of α olefins by α α α trifluoroacetamidinate modified group 4 metal cpamcf3 initiators
    Organometallics, 2019
    Co-Authors: Rick R. Thompson, Peter Y. Zavalij, Lawrence R Sita
    Abstract:

    The C1-symmetric cyclopentadienyl, α,α,α-trifluoroacetamidinate (CPAMCF3) group 4 metal dimethyl complexes, Cp*[N(Et)C(CF3)N(tBu)]M(Me)2 (Cp* = η5-C5Me5) for M = Zr (3) and Hf (4), serve as initiators for the stereoselective (isotactic) living Coordination Polymerization (LCP) of α-olefins upon in situ “activation” using one equiv of the borate co-initiator, [PhNMe2H][B(C6F5)4]. For the LCP of 1-hexene using 4, a six-fold enhancement in the rate of Polymerization, Rp, is observed relative to the LCP of this same α-olefin when the nonfluorinated CPAMCH3 structural analogue, Cp*[N(Et)C(CH3)N(tBu)Hf(Me)2] (2), is employed as the preinitiator. For the LCP of propene, an eight-fold increase in Rp using the CPAMCF3 preinitiator 4 now permits production of practical quantities of highly stereo- and regioregular isotactic polypropene (iPP) under reaction conditions that are not amenable for use with the corresponding CPAMCH3 preinitiator 2. These results provide strong support for a unique synergistic coupling of...

  • Electronic Effect Rate Enhancement in the Stereoselective Living Coordinative Polymerization of α‑Olefins by α,α,α-Trifluoroacetamidinate-Modified Group 4 Metal CPAMCF3 Initiators
    2018
    Co-Authors: Rick R. Thompson, Peter Y. Zavalij, Lawrence R Sita
    Abstract:

    The C1-symmetric cyclopentadienyl, α,α,α-trifluoroacetamidinate (CPAMCF3) group 4 metal dimethyl complexes, Cp*­[N­(Et)­C­(CF3)­N­(tBu)]­M­(Me)2 (Cp* = η5-C5Me5) for M = Zr (3) and Hf (4), serve as initiators for the stereoselective (isotactic) living Coordination Polymerization (LCP) of α-olefins upon in situ “activation” using one equiv of the borate co-initiator, [PhNMe2H]­[B­(C6F5)4]. For the LCP of 1-hexene using 4, a six-fold enhancement in the rate of Polymerization, Rp, is observed relative to the LCP of this same α-olefin when the nonfluorinated CPAMCH3 structural analogue, Cp*­[N­(Et)­C­(CH3)­N­(tBu)­Hf­(Me)2] (2), is employed as the preinitiator. For the LCP of propene, an eight-fold increase in Rp using the CPAMCF3 preinitiator 4 now permits production of practical quantities of highly stereo- and regioregular isotactic polypropene (iPP) under reaction conditions that are not amenable for use with the corresponding CPAMCH3 preinitiator 2. These results provide strong support for a unique synergistic coupling of steric and electronic effects of the CPAMCF3 ligand environment

  • stereoengineering of poly 1 3 methylenecyclohexane via two state living Coordination Polymerization of 1 6 heptadiene
    Journal of the American Chemical Society, 2013
    Co-Authors: Kaitlyn E Crawford, Lawrence R Sita
    Abstract:

    External control over the rate of dynamic methyl group exchange between configurationally stable active species and configurationally unstable dormant species with respect to chain-growth propagation within a highly stereoselective and regiospecific living Coordination Polymerization of 1,6-heptadiene has been used to generate a spectrum of different physical forms of poly(1,3-methylenecyclohexane) (PMCH) in which the stereochemical microstructure has been systematically varied between two limiting forms. The application of this strategy to manipulate the bulk properties of PMCH and the solid-state microphase behavior of well-defined PMCH-b-poly(1-hexene) block copolymers is further demonstrated.

  • ex uno plures out of one many new paradigms for expanding the range of polyolefins through reversible group transfers
    Angewandte Chemie, 2009
    Co-Authors: Lawrence R Sita
    Abstract:

    The "mature" status presently enjoyed by polyolefins prepared with homogeneous (soluble) single-site catalysts through the transition-metal-catalyzed Coordination Polymerization of ethene and 1-alkenes brings with it a common impression that it is now routinely possible to obtain, with a high degree of confidence, any desired stereochemical microstructure or copolymer composition through iterative optimization employing a set of mutationally related synthetic derivatives generated from an initial molecular design. The dominant reliance on this "one catalyst, one material" strategic approach to discovery is intrinsically self-limiting, however, owing to the limited pool of molecular structures that can be reasonably synthesized and drawn upon. Recently, non-chain-terminating, reversible group-transfer processes have been purposefully introduced to olefin Coordination Polymerization. These processes, which are highly competitive with propagation, can be controlled externally and now provide the basis for new "one catalyst, many materials" paradigms that have the potential to greatly expand the reach of polyolefin materials for the 21st century.

  • living coordinative chain transfer Polymerization and coPolymerization of ethene α olefins and α ω nonconjugated dienes using dialkylzinc as surrogate chain growth sites
    Macromolecules, 2008
    Co-Authors: Wei Zhang, Jia Wei, Lawrence R Sita
    Abstract:

    Highly efficient, rapid, and reversible chain transfer between active transition-metal-based propagating centers derived from {Cp*Hf(Me)[N(Et)C(Me)N(Et)]}[B(C6F5)4] (Cp* = η5-C5Me5) (1a) or {Cp*Hf(Me)[N(Et)C(Me)N(Et)]}[B(C6F5)3Me] (1b) and multiple equivalents of dialkylzinc (ZnR2) acting as “surrogate” chain-growth sites has been achieved for establishing the living coordinative chain-transfer Polymerization (CCTP) of ethene, α-olefins, and α,ω-nonconjugated dienes and living CCTP coPolymerization of ethene with α-olefins and α,ω-nonconjugated dienes. These living CCTP processes not only provide a work-around solution to the “one chain per metal” cap on product yield currently limiting traditional living Coordination Polymerization of ethene and α-olefins but, in addition, provide access to practical volumes of a variety of unique new classes of precision polyolefins of tunable molecular weights and very narrow polydispersity (Mw/Mn ≤ 1.1).

Xiaoyu Huang - One of the best experts on this subject based on the ideXlab platform.

Shiping Zhu - One of the best experts on this subject based on the ideXlab platform.

  • elastomeric properties of ethylene 1 octene random and block copolymers synthesized from living Coordination Polymerization
    Polymer, 2015
    Co-Authors: Weifeng Liu, Wenjun Wang, Hong Fan, Xiao Zhang, Shiping Zhu
    Abstract:

    Abstract The elastomeric performance of a series of ethylene/1-octene random and block copolymers prepared from living Coordination Polymerization was studied in this work. All the polymer samples exhibited good toughness. The living random copolymers had better elasticity than commercial metallocene random copolymers. The strain recovery of the living random copolymers was about 90% with an applied strain up to 800%. It was demonstrated that the copolymer elasticity was mainly determined by their block structure, with little influence by their molecular weight. It was also found that either too high or too low content of hard-block content deteriorated the copolymer elastomeric behavior. The diblock copolymer having about 42 wt% hard block content (LBC1) gave the best elasticity among the studied block copolymers and retained the strain recovery about 80% under the applied stain of 600%.

  • structure analysis of ethylene 1 octene copolymers synthesized from living Coordination Polymerization
    European Polymer Journal, 2014
    Co-Authors: Weifeng Liu, Wenjun Wang, Hong Fan, Shiping Zhu
    Abstract:

    Abstract A series of ethylene/1-octene random and block copolymer samples were synthesized via a living Coordination Polymerization catalyzed by bis [ N -(3-methylsalicylidene)-2,3,4,5,6-pentafluoroanilinato] titanium(IV) dichloride/dMAO. The chain microstructures of the copolymers were elucidated by analytic TREF and DSC thermal fractionation techniques in this work. It was found that the living random copolymers possessed narrower intrachain composition distributions than those prepared from conventional metallocene catalysts. With the same short chain branching content, the melting temperature of living random copolymer was about 16 °C lower than metallocene-catalyzed random copolymer. The living block copolymers were also studied in comparison with the olefin multiblock copolymer (OBC) produced from chain shuttling Polymerization. The interchain composition distribution of OBC was found broader than living block copolymers. However, the crystal thickness distribution of OBC was narrower. The diblock copolymer had a bimodal distribution in the crystal thickness and the step triblock copolymer showed a trimodal distribution, in contrast to OBC’s single modal distribution.