原子转移自由基聚合的最新研究进展*

原子转移自由基聚合(ATRP)是目前为止最具工业化应用前景的“活性”/可控自由基聚合之一。近年来对其广泛的研究使这一技术逐渐向着“提高可操作性”与“尽可能地减少金属催化剂用量”方面发展;与此同时,诞生了不同催化体系的ATRP衍生技术,如反向原子转移自由基聚合(RATRP)、正向反向同时引发的原子转移自由基聚合(SR&NI ATRP)、引发剂连续再生催化剂原子转移自由基聚合(ICAR ATRP)、电子转移生成催化剂的原子转移自由基聚合(AGET ATRP)和电子转移再生催化剂原子转移自由基聚合(ARGET ATRP)等多种基于ATRP的新方法。本文概述了这几种ATRP体系的发展历程与基本原理,并对其国内外的最新研究进展进行了综述。     

乳液原子转移自由基聚合*

原子转移自由基聚合(ATRP)应用于乳液聚合体系的主要挑战在于如何同时保证乳液的稳定性和聚合反应的可控性。本文主要对乳液ATRP体系中影响聚合反应可控性和乳液稳定性的各种因素、乳液ATRP的机理和乳液ATRP的应用等方面进行了综述。表面活性剂亲水亲油性及其亲水亲油基团的化学性质、催化剂/配体在油/水两相之间的分配行为、引发剂的溶解性、反应温度以及各组分的浓度是影响反应可控性和乳液稳定性的主要因素。各组分在油/水两相中的分配行为使得乳液ATRP的机理比传统乳液聚合更加复杂。乳液原子转移自由基聚合结合了活性自由基聚合和乳液聚合的优点,在理论研究和工业生产上具有很大的应用前景。     

原子转移自由基聚合研究进展

原子转移自由基聚合(Atom transfer radical polymerization,ATRP)是一种发展较快的可控/活性聚合技术,现已广泛应用于聚合物分子结构设计及众多功能高分子材料的合成.本文在综述了ATRP的反应机理的基础上,介绍了引发剂、催化剂、配体、单体等对ATRP的影响,同时综述了降低(或去除)金属盐含量的绿色、高效ATRP聚合体系,如引发剂持续再生活化ATRP,电子转移生成(再生)活化剂ATRP,铁催化体系,光催化体系等.近年来发展的无金属光诱导的有机催化ATRP聚合体系也做了综述.     

新型引发体系引发MMA"活性"自由基聚合

传统的原子转移自由基聚合(ATRP)引发体系是由卤化物(引发剂)、低价过渡金属和合适的配体组成的络合物(催化剂)[1,2],即RX/Mnt/LX,三部分组成的.但由于卤化物的毒性和低价过渡金属易被空气中的氧气氧化,因此Matyjaszewski等[3,4]和Teyssié等[5]提出了新的引发体系反向ATRP.反向ATRP用传统引发剂(如AIBN)代替卤化物,用高价过渡金属络合物代替原来的催化体系,即AIBN/Mn+1t/LX,就避免了上述两个缺点.反向ATRP的引发反应机理表述如下:　　目前已见诸报道的关于反向ATRP的文献甚少[3～5],所使用的引发剂均为AIBN.Wang和Matyja…     

含有热引发转移终止剂的引发体系在反向原子转移自由基聚合中的应用

原子转移自由基聚合 (ATRP)是实现活性聚合的一种颇为有效的途径 ,可以实现多种单体的活性自由基聚合 .反向原子转移自由基聚合 (ReverseATRP)的概念始提出于 1995年 ,是对传统ATRP的改进和拓展 .近年来关于此体系的引发剂的拓展、过渡金属及单体的适用性都得到了很大发展 .本文简要综述了我们研究组在反向原子转移自由基聚合方面的研究进展     

N,N-二乙基硫代氨基甲酰硫基团(S_2CNEt_2)为假卤原子转移的原子转移自由基聚合新体系

综述了原子转移自由基聚合 (ATRP)中 ,以N ,N 二乙基硫代氨基甲酰硫基团 (S2 CNEt2 )转移实现活性聚合、控制聚合物结构的 4种新方法 :非卤化物 ,N ,N 二乙基二硫代氨基甲酸亚铜 [Cu(S2 CNEt2 ) ]催化甲基丙烯酸甲酯 (MMA)的正向ATRP ;2 ,2′ 联吡啶存在的条件下 ,过氧化苯甲酰 (BPO)与Cu(S2 CNEt2 )的氧化还原反应控制MMA的本体反向ATRP;同时含可转移卤原子、基团的氯化二乙基二硫代氨基甲酸铜 [Cu(S2 CNEt2 ) Cl]成功地用于偶氮二异丁腈或BPO引发的乙烯类单体反向ATRP.假卤原子S2 CNEt2 转移的ATRP得到窄分布的精确结构聚合物分子链ω 端含有光敏基团S2 CNEt2 ,可引发乙烯类单体的常温光聚合 ,实现ATRP与光聚合相结合制备嵌段共聚物     

自由基聚合近20年的发展

自由基聚合是在上世纪50年代发展起来的,已成为工业生产高分子产品的重要技术。自由基聚合由通用自由基聚合而发展为今天的活性/控制自由基聚合,是近20多年的事情。通用自由基合的研究主要是高活性引发剂、氧化还原体系及多功能引发体系,ESR和激光技术在动力学和自由基精细结构测定的应用等。而活性自由基聚合由最初的引发转移终止剂活性自由基聚合(iniferter),演变为氮氧自由基调控聚合(NMP)或稳定自由基聚合(SFRP),原子转移自由基聚合(ATRP),茂钛金属/环氧化物自由基开环引发聚合,可逆加成断裂链转移(RAFT)聚合,碘转移自由基聚合和有机碲、有机锑调控聚合等活性/控制自由基聚合。本文就以上各方面的研究进展进行简要的综述。     

原子转移自由基聚合引发体系的最新研究

本文介绍了关于原子转移自由基聚合(ATRP)引发-活化-失活过程的最新研究情况,包括RATRP、SR&NI ATRP、AGET ATRP、ARGET ATRP以及ICAR ATRP等新型ATRP引发体系.这些新型ATRP体系克服了通常ATRP体系的缺点,比如低价态过渡金属催化剂容易氧化和用量过大的问题,而采用高价态过渡金属催化剂,并极大降低了其用量.尤其是后两种体系仅需微量(1-50ppm)、价态稳定的过渡金属络合物控制聚合反应的进行,使其成为一种适合于工业化生产的活性可控聚合技术.本文同时介绍了杂化及双金属ATRP催化体系,这两种新型催化体系具有较高的催化活性和对聚合反应的调控能力,且通过简单地过滤或沉降就可从聚合产物中脱除.     

原子转移自由基聚合及其催化引发体系研究进展

原子转移自由基聚合(ATRP)作为一种有效的"活性"/可控聚合可对聚合物进行分子设计,制备结构和相对分子质量可控的各类聚合物,具有潜在而广泛的研究价值。本文综述了ATRP的研究进展,特别是对传统ATRP催化引发体系、RATRP催化引发体系、AGET ATRP催化引发体系、SR&NI ATRP催化引发体系、ICAR ATRP催化引发体系、ARGET ATRP催化引发体系、杂化或双金属催化体系等的催化引发机理进行了详细的介绍。并综述了ATRP聚合中各种实施方法如本体聚合法、溶液聚合法、悬浮聚合法、乳液聚合法等的研究现状。     

原子转移自由基聚合引发体系的最新研究进展

本文介绍了关于原子转移自由基聚合（ATRP）引发-活化-失活过程的最新研究情况,包括RATRP、SR&NI ATRP、AGET ATRP、ARGET ATRP以及ICAR ATRP等新型ATRP引发体系。这些新型ATRP体系逐渐克服了通常ATRP体系的局限性,尤其是后两种体系仅需微量（1～50 ppm）价态稳定的过渡金属络合物调控聚合,大大简化了ATRP方法的工业化生产程序;本文同时介绍了杂化及双金属ATRP催化体系,这两种新型催化体系具有较高的催化活性和对聚合反应的调控能力,而且通过简单地过滤或沉降就可从聚合产物当中脱除。     

Preparation of homopolymers and block copolymers in miniemulsion by ATRP using activators generated by electron transfer (AGET)

A new initiating/catalytic system for atom transfer radical polymerization (ATRP) is reported. This system starts with alkyl halides as initiators and transition metal complexes in their oxidatively stable state (e.g., Cu(II)Br2/ligand) as catalysts. The activators are generated by electron transfer (AGET) without involvement of initiating organic radicals. AGET ATRP has a significant advantage over simultaneous reverse and normal initiation (SR&NI) ATRP, because it provides a simple route for synthesizing pure polymers with complex architectures such as star copolymers, block copolymers, etc. Furthermore, AGET ATRP can be also successfully carried out in miniemulsion. Homopolymers and pure block copolymers were successfully synthesized via ATRP in miniemulsion using AGET ATRP. The final products were analyzed via two-dimensional chromatography, which combines high performance liquid chromatography (HPLC) and gel permeation chromatography (GPC). The resulting chromatograms showed that pure linear block copolymers and star block copolymers were prepared without the presence of any homopolymers.     

AGET ATRP in water and inverse miniemulsion: A facile route for preparation of high‐molecular‐weight biocompatible brush‐like polymers

Activators generated by electron transfer for atom transfer radical polymerization (AGET ATRP) of oligo(ethylene glycol) monomethyl ether methacrylate (OEOMA) was investigated in homogeneous aqueous solution targeting DP = 1000, and in inverse miniemulsion targeting DP = 600, at 30 °C. Several reaction parameters were examined in the preparation of biocompatible, brush‐like, high‐molecular‐weight, water‐soluble polymers. They include concentration of ascorbic acid (AscA), ratio of water to OEOMA, mode of addition of AscA, and ratio of initiator to Cu(II) complex. The results obtained in these studies indicate that AGET ATRP retains all of the benefits of normal ATRP and, additionally, provides a facile route for the preparation of well‐controlled high‐molecular‐weight polymers because of the use of oxidatively stable catalyst precursors. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1771–1781, 2009     

AGET ATRP in the Presence of Air in Miniemulsion and in Bulk

Summary: The recently developed initiation system, activators generated by electron transfer (AGET), is used in atom transfer radical polymerization (ATRP) in the presence of a limited amount of air. Ascorbic acid and tin(II ) 2‐ethylhexanoate are used as reducing agents in miniemulsion and bulk, respectively. An excess of reducing agent consumes the oxygen present in the system and, therefore, provides a deoxygenated environment for ATRP. ATRP of butyl acrylate is successfully carried out in miniemulsion and in the presence of air. During polymerization the radical concentration remains constant. The polymerization reaches over 60% monomer conversion after 6 h, which results in polymers with a predetermined molecular weight = 14 000 g · mol⁻¹ and a low polydispersity ( = 1.23). AGET ATRP of styrene is also successful in bulk in the presence of air, as evidenced by linear semi‐logarithmic kinetics, which leads to polystyrene with an of 13 400 g · mol⁻¹ and a low polydispersity index ( = 1.14).

Appearance of miniemulsion before and after the reducing agent ascorbic acid was added (left); and GPC traces representing molecular weights during the AGET ATRP of BA in miniemulsion in the presence of air (right).     

Photoirradiated Fe-Mediated AGET ATRP of Methyl Methacrylate in the Presence of Alcohol

In this study, photoirradiated Fe-mediated AGET (activators generated by electron transfer) atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) was investigated at ambient temperature in N,N-dimethylformamide (DMF) using carbon tetrachloride as initiator, FeCl₃·6H₂O/bipyridine (Bpy) as catalyst complex, and alcohol as reducing agent. Linear semi-logarithmic plot of conversion vs. time was obtained from the kinetic experiments, and the number-average molecular weight increased linearly with monomer conversion and corresponded to the theoretic values with molecular weight distributions (M_w/M_n) as low as 1.25, which agreed with the character of controlled/living polymerization. The kinds of alcohol played an important role in photoirradiated Fe-mediated AGET ATRP of MMA. The living characteristics were demonstrated through chain extension experiment. The obtained polymer was characterized by proton nuclear magnetic resonance (NMR) and gel permeation chromatography.     

Copper(0)‐mediated living radical polymerization of acrylonitrile: SET‐LRP or AGET‐ATRP

Cu(0)‐mediated living radical polymerization was first extended to acrylonitrile (AN) to synthesize polyacrylonitrile with a high molecular weight and a low polydispersity index. This was achieved by using Cu(0)/hexamethylated tris(2‐aminoethyl)amine (Me₆‐TREN) as the catalyst, 2‐bromopropionitrile as the initiator, and dimethyl sulfoxide (DMSO) as the solvent. The reaction was performed under mild reaction conditions at ambient temperature and thus biradical termination reaction was low. The rapid and extensive disproportionation of Cu(I)Br/Me₆‐TREN in DMSO/AN supports a mechanism consistent with a single electron transfer‐living radical polymerization (SET‐LRP) rather than activators generated by electron transfer atom transfer radical polymerization (AGET ATRP). ¹H NMR analysis and chain extension experiment confirm the high chain‐end functionality of the resultant polymer. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2010     

碱性离子液体催化金属调节的甲基丙烯酸甲酯的电子转移活化原子转移自由基聚合

通过电子转移活化原子转移自由基聚合（AGET ATRP）,以2-溴代异丁酸乙酯（EBiB）为引发剂、维生素C（VC）为还原剂。 以碱性离子液体1-丁基-3-甲基咪唑氢氧化盐([Bmim][OH])分别和FeCl3·6H2O、CuCl2及RuCl3形成的配合物为催化剂催化甲基丙烯酸甲酯（MMA）的本体和溶液聚合。 催化量的[Bmim][OH]即可提高聚合速率,并且得到相对分子质量分布可控的PMMA（Mw/Mn为1.20～1.40）。 研究了[Bmim][OH]的加入量对聚合速率和相对分子质量分布的影响,3种催化体系催化性质通过循环伏安曲线表征。 扩链反应证明了碱性离子液体催化甲基丙烯酸甲酯的聚合为“活性”/可控自由基聚合。 碱性离子液体良好的溶解性使其成为活性自由基聚合的良好催化剂。     

Atom transfer radical polymerization in aqueous dispersed media

During the last decade, atom transfer radical polymerization (ATRP) received significant attention due to its exceptional capability of synthesizing polymers with pre-determined molecular weight, well-defined molecular architectures and various functionalities. It is economically and environmentally attractive to adopt ATRP to aqueous dispersed media, although the process is challenging. This review summarizes recent developments of conducting ATRP in aqueous dispersed media. The issues related to retaining “controlled/living” character as well as colloidal stability during the polymerization have to be considered. Better understanding the ATRP mechanism and development of new initiation techniques, such as activators generated by electron transfer (AGET) significantly facilitated ATRP in aqueous systems. This review covers the most important progress of ATRP in dispersed media from 1998 to 2009, including miniemulsion, microemulsion, emulsion, suspension and dispersed polymerization.      

Synthesis of poly(2‐hydroxyethyl methacrylate) in protic media through atom transfer radical polymerization using activators generated by electron transfer

Atom transfer radical polymerization (ATRP) using activators generated by electron transfer (AGET) was investigated for the controlled polymerization of 2‐hydroxyethyl methacrylate (HEMA) in a protic solvent, a 3/2 (v/v) mixture of methyl ethyl ketone and methanol. The AGET process enabled ATRP to be started with an air‐stable Cu(II) complex that was reduced in situ by tin(II) 2‐ethylhexanoate. The reaction temperature, Cu catalysts with different ligands, and variation of the initial concentration ratio of HEMA to the initiator were examined for the synthesis of well‐controlled poly(2‐hydroxyethyl methacrylate) and a poly(methyl methacrylate)‐b‐poly(2‐hydroxyethyl methacrylate) block copolymer. The level of control in AGET ATRP was similar to that in normal ATRP in protic solvents, and this resulted in a linear increase in the molecular weight with the conversion and a narrow molecular weight distribution (weight‐average molecular weight/number‐average molecular weight < 1.3). © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3787–3796, 2006