Toward self-assembling dendritic macromolecules from conventional monomers by a combination of living radical polymerization and irreversible terminator multifunctional initiator

TERMINI stands for irreversible terminator multifunctional initiator and represents a new concept elaborated in our laboratory for the design of novel macromolecules with complex architecture from a diversity of commercial monomers. TERMINI is a masked multifunctional initiator that quantitatively interrupts a living polymerization. After demasking, the TERMINI-derived repeat unit provides access to a quantitative reinitiation of the same living polymerization in more than one direction, thus becoming a branching point. In this article, with a combination of self-regulated metal-catalyzed living radical polymerization and TERMINI, we demonstrate a new method for the divergent synthesis of dendritic poly(methyl methacrylate) containing a bifunctional core at its focal point. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 505–513, 2004     

Accelerated iterative strategy for the divergent synthesis of dendritic macromolecules using a combination of living radical polymerization and an irreversible terminator multifunctional initiator

Our laboratory has reported the elaboration of an iterative strategy for the synthesis of dendritic macromolecules from conventional monomers. This synthetic method involves a combination of self‐regulated metal‐catalyzed living radical polymerization initiated from arenesulfonyl chlorides and an irreversible terminator multifunctional initiator (TERMINI). The previous TERMINI, (1,1‐dimethylethyl)[[1‐[3,5‐bis(S‐phenyl‐4‐N,N′ diethylthiocarbamate)phenyl]ethenyl]oxy]dimethylsilane, was prepared in nine reaction steps. The replacement of the previous TERMINI with one that requires only three steps for its synthesis, diethylthiocarbamic acid S‐{3‐[1‐(tert‐butyl‐dimethyl‐silanyloxy)‐vinyl]‐5‐diethylcarbamoylsulfanyl‐phenyl} ester, and the use of the more reactive Cu₂S/2,2′‐bipyridine rather than the Cu₂O/2,2′‐bipyridine self‐regulated catalyst have generated an accelerated method for the synthesis of dendritic macromolecules. This method provides rational design strategies for the synthesis of dendritic macromolecules with different compaction by the use of a single monomer. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4894–4906, 2005     

Combination of an anionic terminator multifunctional initiator and divergent carbanionic polymerization: application to the synthesis of dendrimer-like polymers and of asymmetric and miktoarm stars

A new and versatile synthetic strategy that provides access to precisely defined and totally soluble multicarbanionic initiators has been implemented to obtain by divergent growth dendrimer-like samples of polystyrene (PS) (up to the seventh generation) or polybutadiene (PB) (up to the third generation) and also asymmetric and miktoarm stars. This strategy rests on lithium-halide exchange reactions to generate multicarbanionic species and on the design of an original reagent that can concomitantly react with living carbanionic chains/arms to deactivate them and produce multicarbanionic sites after exchange of its bromides against lithium. This reagent, 4,4'-dibromodiphenylethylene (1), functions as a TERminating agent and a Multifunctional INItiator (TERMINI), according to a concept first proposed by Percec in another context. Upon using this anionic TERMINI in living carbanionic polymerization and repeating the two steps of chain end derivatization by 1 and divergent arm growth from the multifunctional sites generated, perfectly defined dendrimer-like polystyrene and polybutadiene could be obtained up to the seventh generation for the former and up to the third generation for the latter. Each step, i.e., chain end modification and arm growth, was carefully monitored, and the dendrimer-like samples of PS and PB were all characterized by size exclusion chromatography equipped with a multiangle laser light scattering detector (SEC/LS) and high-temperature size exclusion chromatography equipped with a viscometric detector (HT-SEC). The viscosity behavior of these dendrimer-like polystyrenes--bell-shaped variation versus the number of generation--was found to be similar to that reported for regular dendrimers. This chemistry, namely this anionic TERMINI, was also exploited to derive three-arm asymmetric and miktoarm stars.     

A novel consecutive chain transfer reaction to p-methylstyrene and hydrogen during metallocene-mediated olefin polymerization.

This paper describes the first example of consecutive chain transfer reaction, first to p-methylstyrene (or styrene) and then to hydrogen, during metallocene-catalyzed propylene polymerization by rac-Me(2)Si[2-Me-4-Ph(Ind)](2)ZrCl(2)/MAO complex. The PP molecular weight is inversely proportional to the molar ratio of [p-methylstyrene]/[propylene] and [styrene]/[propylene] with the chain transfer constants of k(tr)/k(p) = 1/6.36 and 1/7.5, respectively. Although hydrogen does not influence the polymer molecular weight, it greatly affects the catalyst activity. Each PP chain formed contains a terminal p-methylstyrene (or styrene) unit. The terminal p-MS unit can be metalated to form a stable polymeric anion for living anionic polymerization to prepare new PP diblock copolymers, such as PP-b-PS, which are very difficult to prepare by other methods. The overall process resembles a transformation reaction from metallocene to living anionic polymerization.     

High‐Molecular‐Weight Polynucleotides by Transferase‐Catalyzed Living Chain‐Growth Polycondensation

We present terminal deoxynucleotidyl transferase‐catalyzed enzymatic polymerization (TcEP) for the template‐free synthesis of high‐molecular‐weight, single‐stranded DNA (ssDNA) and demonstrate that it proceeds by a living chain‐growth polycondensation mechanism. We show that the molecular weight of the reaction products is nearly monodisperse, and can be manipulated by the feed ratio of nucleotide (monomer) to oligonucleotide (initiator), as typically observed for living polymerization reactions. Understanding the synthesis mechanism and the reaction kinetics enables the rational, template‐free synthesis of ssDNA that can be used for a range of biomedical and nanotechnology applications.     

聚醋酸乙烯酯的光引发可控合成——介绍一个高分子化学综合实验

本实验开展了醋酸乙烯酯的可逆加成-断裂链转移自由基聚合(RAFT),分别运用偶氮二异丁腈(AIBN)引发和可见光引发两种方式进行了聚合反应,运用核磁共振和凝胶色谱等多种手段对所得聚合物结构进行了表征与分析。通过比较AIBN引发与光引发所获得聚合物端基结构的异同,加深了学生对RAFT聚合方法原理的理解。同时,运用该方法实现了聚合物两端端基结构的高度功能化,深入体会聚合物合成设计概念。本综合实验教学不仅通过对比法加深了学生对实验原理和专业知识的理解,提升了学生创新研究能力,而且训练了学生的实验操作技能、大型仪器使用能力和结果分析能力,提升了综合素质。     

Synthesis of well‐defined comb‐like graft (co)polymers by nucleophilic substitution reaction between living polymers and polyhalohydrocarbon

A series of graft (co)polymers were synthesized by nucleophilic substitution reaction between iodinated 1,2‐polybutadiene (PB‐I, backbone) and living polymer lithium (side chains). The coupling reaction between PB‐I and living polymers can finish within minutes at room temperature, and high conversion (up to 92%) could be obtained by effectively avoiding side reaction of dimerization when living polymers were capped with 1,1‐diphenylethylene. By virtue of living anionic polymerization, backbone length, side chain length, and side chain composition, as well as graft density, were well controlled. Tunable molecular weight of graft (co)polymers with narrow molecular weight distribution can be obtained by changing either the lengths of side chain and backbone, or the graft density. Graft copolymers could also be synthesized with side chains of multicomponent polymers, such as block polymer (polystyrene‐b‐polybutadiene) and even mixed polymers (polystyrene and polybutadiene) as hetero chains. Thus, based on living anionic polymerization, this work provides a facile way for modular synthesis of graft (co)polymers via nucleophilic substitution reaction between living polymers and polyhalohydrocarbon (PB‐I). © 2013 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

含咪唑离子盐的环辛烯在离子液体中开环易位聚合微观研究

用核磁共振方法研究了带电荷的环辛烯单体在离子液体和CDCl3中开环易位聚合反应的微观特征,根据单体在化学位移δ=5.66~5.58处双键氢积分峰面积的减少和聚合物主链上不饱和双键氢移至高场δ=5.38~5.39处峰面积积分的增加来表征聚合反应的情况.检测和记录了单体在有离子液体参与的条件下均相聚合反应和在CDCl3中的异相聚合反应过程,根据在不同反应体系中Grubbs第二代崔化剂中与Ru相连的苯亚甲基上氢在核磁图谱上δ=19.2处的峰型变化,探讨在两种介质中的不同聚合行为.研究表明,该单体在离子液体介质中的均相聚合有可控聚合的微观特点,并通过ln[M]0/[M]与反应时间的关系曲线,证实了反应的活性特征.     

可逆加成-断裂链转移活性自由基聚合的应用研究进展

可逆加成-断裂链转移(Reversible addition-fragmentation chain transfer,RAFT)自由基聚合是活性自由基聚合领域的一次突破.由于该方法具有适用单体范围广、反应条件温和以及聚合实施方法多样等优点,已成为一种有效的分子设计和材料设计手段.它不但可实现聚合物链端及链段侧基的功能化和制备特定空间拓扑结构的大分子,比如嵌段、星型、梳状及链端氨基聚合物等,还可用于修饰固体材料表面及生物大分子来赋予其特殊的功能.本文综述了RAFT技术在实际应用中的实施研究进展.     

Cu(0) Wire-mediated Single-electron Transfer-living Radical Polymerization of Oligo(ethylene oxide) Methyl Ether Acrylate by Selecting the Optimal Reaction Conditions

The efficient Cu(0) wire-catalyzed single-electron transfer-living radical polymerization (SET-LRP) in organic solvents and mixtures of the organic solvents with water has been thoroughly investigated.Oligo(ethylene oxide) methyl ether acrylate was used as an exemplar oligomer monomer to determine the optimum polymerization conditions for rapid,controlled,and quantitative production of well-defined polymers.The effects of Cu(0)-wire length (12.5 or 4.5 cm),ligand type (tris(dimethylaminoethyl)amine,Me6-TREN,or tris(2-aminoethyl)amine,TREN),and solvent type (dipolar aprotic solvents,cyclic ethers,alcohol,or acetone) on the polymerization have been evaluated.Kinetic experiments were performed for all polymerizations to assess the "living" behavior of each system employed.Importantly,TREN could be used as a replacement for Me_6-TREN in Cu(0) wire-catalyzed SET-LRP of oligomer monomer,which probably provides the most economical and efficient methodology since TREN is 80 times less expensive than Me6-TREN.The high chain-end fidelity of resulting polymer was experimentally verified by thiol-Michael addition reaction at the a-Br chain end and subsequent chain extension with methyl acrylate.     

再活化链式聚合

基于传统的链式聚合和逐步聚合二种高分子链增长过程,提出了再活化链式聚合。按此聚合机理,高分子的链增长是通过将一个非活性或睡眠状态的链(Mm)重新活化为活性种(Mm*),活性种再和一个单体(M)反应,生成一个较大分子量的休眠产物(Mm 1)来实现的。再活化链式聚合主要例子包括苯胺和或许其它芳香族单体的氧化聚合,活性自由基聚合,以及核酸和蛋白质合成中的生物聚合。     

Efficient Synthesis of Poly(acrylic acid) in Aqueous Solution via a RAFT Process

The direct polymerization of acrylic acid (AA) in aqueous solution for high molecular weight by means of living radical polymerization is still difficult. Here, AA was polymerized homogeneously in water by a reversible addition-fragmentation transfer polymerization (RAFT) in the presence of a water-soluble trithiocarbonate as a RAFT agent. Various ratios [AA]:[RAFT agent] were investigated to aim at different molecular weights. The polymerization exhibited living free-radical polymerization characteristics at different ratios [AA]: [RAFT agent]: controlled molecular weight, low polydispersity and well-suited linear growth of the number-average molecular weight, M _n with conversion. The chain transfer to solvent or polymer was suppressed during the polymerization process, thus high linear PAA with high molecular weight and low PDI can be obtained. Moreover, using the generated PAA as a macro RAFT agent, the chain extension polymerization of PAA with fresh AA displayed controlled behavior, demonstrated the ability of PAA to reinitiate sequential polymerization.     

Selective one-pot synthesis of trithiocarbonates, xanthates, and dithiocarbamates for use in RAFT/MADIX living radical polymerizations

[reaction: see text] We report a facile route for the production of chain transfer agents for reversible addition fragmentation chain transfer (RAFT) and macromolecular design via the interchange of xanthates (MADIX) polymerizations, via a one-pot reaction. 1,1'-Thiocarbonyl diimidazole (TCDI) undergoes controlled monosubstitution when reacted with secondary thiols or alcohols. The intermediate S/O-esters of imidazole-N-thionocarboxylic acid react efficiently with a range of primary thiols, alcohols, and amines to form asymmetrical dithiocarbonates, trithiocarbonates, and dithiocarbamates, respectively. The synthesis provides a facile approach to the controlled radical polymerization of vinyl monomers through the reversible addition-fragmentation chain transfer (RAFT) mechanism.     

High‐Speed Living Polymerization of Polar Vinyl Monomers by Self‐Healing Silylium Catalysts

This contribution describes the development and demonstration of the ambient‐temperature, high‐speed living polymerization of polar vinyl monomers (M) with a low silylium catalyst loading (≤ 0.05 mol % relative to M). The catalyst is generated in situ by protonation of a trialkylsilyl ketene acetal (^RSKA) initiator (I) with a strong Brønsted acid. The living character of the polymerization system has been demonstrated by several key lines of evidence, including the observed linear growth of the chain length as a function of monomer conversion at a given [M]/[I] ratio, near‐precise polymer number‐average molecular weight (M_n, controlled by the [M]/[I] ratio) with narrow molecular weight distributions (MWD), absence of an induction period and chain‐termination reactions (as revealed by kinetics), readily achievable chain extension, and the successful synthesis of well‐defined block copolymers. Fundamental steps of activation, initiation, propagation, and catalyst “self‐repair” involved in this living polymerization system have been elucidated, chiefly featuring a propagation “catalysis” cycle consisting of a rate‐limiting C? C bond formation step and fast release of the silylium catalyst to the incoming monomer. Effects of acid activator, catalyst and monomer structure, and reaction temperature on polymerization characteristics have also been examined. Among the three strong acids incorporating a weakly coordinating borate or a chiral disulfonimide anion, the oxonium acid [H(Et₂O)₂]⁺[B(C₆F₅)₄]^? is the most effective activator, which spontaneously delivers the most active R₃Si⁺, reaching a high catalyst turn‐over frequency (TOF) of 6.0×10³ h^?1 for methyl methacrylate polymerization by Me₃Si⁺ or an exceptionally high TOF of 2.4×10⁵ h^?1 for n‐butyl acrylate polymerization by iBu₃Si⁺, in addition to its high (>90 %) to quantitative efficiencies and a high degree of control over M_n and MWD (1.07–1.12). An intriguing catalyst “self‐repair” feature has also been demonstrated for the current living polymerization system.     

Novel methodology for the synthesis of N-alkoxyamines

[reaction: see text] We report a new methodology for the synthesis of the N-alkoxyamines, which can be used as initiators in "living" free radical polymerization. Silyl radical abstraction from alkyl halides allows the synthesis of N-alkoxyamines inaccessible by other methods.     

基于巯基点击反应与RAFT聚合的功能性聚合物合成

可逆加成-裂解链转移聚合(RAFT)由于单体适用面广、聚合条件温和、不受聚合方法的限制等特性, 已经成为活性合成聚合物的有效手段之一。点击化学(click chemistry)由于具有良好的选择性、模块性以及官能团耐受性等特点迅速成为许多研究领域,如药物、聚合物、功能材料等合成的有力工具,同时涌现出了多种基于巯基的点击反应。本文综述了近年来基于巯基的点击反应, 如巯基-烯、巯基-炔、巯基-异氰酸酯、巯基-环氧化物以及巯基-卤代烃等新型点击反应与RAFT聚合相结合在功能性聚合物的制备和修饰中的应用, 相信这两种手段的结合将在其中发挥积极的作用。     

From linear side-chain functionalized poly(vinyl ether)s to functional macrocycles

This paper deals with the synthesis of functional polymers of controlled chain dimensions and architecture from poly(chloroalky1 vinyl ether)s. The living polymerization of chloroalkyl vinyl ethers initiated by HX/ZnX₂ systems, and the chemical substitution of the pendant chlorines by various organic functions and groups, in order to generate specific polymer properties are first discussed. Also based on the living character of the polymerizations, the preparation of poly(chloroethyl vinyl ether) with monomacrocyclic and plurimacrocyclic architectures as well as their characterization are then reported. Some evidence for specific host–guest interactions between large organic molecules and polymacrocycles is also presented.     

Conducting Block Copolymer Nanowires Containing Regioregular Poly(3‐Hexylthiophene) and Polystyrene

Grignard Metathesis polymerization (GRIM) for the synthesis of regioregular poly(3‐alkylthiophenes) proceeds via a “living” chain growth mechanism. Due to the “living” nature of this polymerization regioregular poly(3‐alkylthiophenes) with predetermined molecular weight, narrow molecular weight distributions and desired chain end functionality are now readily available. Allyl terminated poly(3‐hexylthiophene) was successfully used as a precursor for the synthesis of di‐block copolymers containing polystyrene. The addition of “living” poly(styryl)lithium to the allyl terminated regioregular poly(3‐hexylthiophene) generated the di‐block copolymer. Poly(3‐hexylthiophene)‐b‐polystyrene was also synthesized by atom transfer radical polymerization. Integration of poly(3‐hexylthiophene) in di‐block copolymers with polystyrene leads to the formation of nanowire morphology and self‐ordered conducting nanostructured materials.     

Synthesis of block copolymers consisting of liquid crystalline and amorphous segments by living/controlled radical polymerization

Living polymerization is most often observed in systems where the growing species are ions. In such systems the chain ends do not react to each other due to elestrostactic repulsion, but only to monomers allowing, this way, the control in structure of the formed polymer. Free radicals, which are the growing species in the radical polymerization, easely undergo combination and prevent a living radical polymerization. Thus, a great challenge to polymer science was in meeting a system that offered to the radical polymerization a radical stabillization alike in ionic polymerizations. At the same time, the radicals should undergo rapid propagation and should not be able to initiate new chains, in a controlled reaction. Some succesfull techniques of living/controlled radical polymerization, such as stable free radical polymerization (SFRP), mediated by nitroxide, INIFERTER and atom transfer polymerization (ATRP) will be overviewed here, as well as their application to the synthesis of liquid crystalline polymers.     

环境友好的可控自由基聚合*

近年来,我们以环境友好、简便快捷、活泼可控、单体普适性强的光活化室温RAFT聚合为主攻目标,针对长波紫外或可见光活化室温RAFT聚合反应特征及其应用展开了深入探讨。研究表明,作为RAFT聚合链转移剂的硫酯化合物具有分别在紫外光和可见光波段的双波段光吸收特征。短波紫外光强吸收,导致硫酯键的光解。然而,可见光波段弱的光吸收则活化其自由基加成产物的断裂反应,加速室温RAFT过程并确保聚合反应的活性特征。高效光引发,可显著缩短RAFT聚合引发期。通过光开关,可实时启动或终止聚合。与常规热聚合不同,室温以下这类聚合反应不存在明显的热活化效应。由此,我们创建了环境友好、单体普适性强、快速可控、通过光开关可实时控制聚合反应启动或终止的光活化室温RAFT聚合,将其成功拓展到太阳光和水溶液聚合体系,并运用于温和条件下新兴水溶性温敏高分子、仿生光响应高分子的快捷可控合成。