原子转移自由基聚合的催化剂再生机理与聚合可控

催化剂再生即向反应体系中加入各种不同形式的＂还原剂＂保证催化剂的活性使聚合反应得以进行。文中介绍了几种原子转移自由基聚合（ATRP）催化剂再生的引发体系,包括电子转移产生催化剂引发ATRP（AGET ATRP）,连续活化剂再生引发剂引发ATRP（ICAR ATRP）,单电子转移活性自由基聚合（SET LRP）,过量单体...     

原子转移自由基聚合的最新研究进展

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进展,包括RATRP 体系克服了常规ATRP 体系中低价态过渡金属催化剂容易氧化的问题,AGET ATRP 体系显著降低了过渡金属化合物的用量,ARGET ATRP体系中残存的过渡金属催化剂仅为(1～50)×10-6, 很多情况下不需要进行后处理,使其适合工业化生产成为可能.同时介绍了ATRP在表面接枝上的应用,表面引发ATRP反应能改善材料的表面特性,同时具有接枝链分子量及分布可控和高接枝率的优点,使其在很多方面都获得了广泛的应用,包括使材料表面图案化、提高材料表面的生物相容性、制备梳型的聚合物刷以及在纳米磁铁矿和真丝表面引发的ATRP反应.     

Fe(Ⅲ)催化苯乙烯的AGET-ATRP法合成

电子活化再生原子转移自由基聚合(AGET ATRP)是近年来原子转移自由基聚合(ATRP)发展的一种新的合成方法。文中选用FeCl3.6H2O为催化剂,三苯基磷(PPh3)为配体,抗坏血酸(AsAc)为还原剂,溴化苄(BzBr)为引发剂,采用AGET ATRP法在110℃用本体聚合的方式成功合成了分子量可控的聚苯乙烯。结果表明,其本体聚合优于溶液聚合;在110℃时,n(St)/n(BzBr)/n(FeCl3.6H2O)/n(PPh3)/n(AsAc)=100/1/1/3/0.5时,聚苯乙烯的-Mn,GPC=6371,且分子量分布较窄(PDI=1.36)。聚合过程表现出"活性"/可控聚合的特征。     

基于原子转移自由基聚合的无机纳米粒子表面接枝改性方法研究进展

综述了原子转移自由基聚合法、反向原子转移自由基聚合法、电子转移生成催化剂原子转移自由基聚合法、电子转移活化再生催化剂原子转移自由基聚合法在无机纳米粒子表面接枝聚合物的研究进展,介绍了聚合物接枝改性过程中不同催化体系的特点。采用上述方法在无机纳米粒子表面接枝改性,均能有效控制纳米复合粒子的粒径及其分布,提高纳米粒子的分散性、耐久性和相容性且反应条件简单、可控性强,是前景广阔的聚合方法。     

ATRP引发剂的非正常引发EI北大核心

通常只能与低价过渡金属卤化物/络合剂配合才能引发原子转移自由基聚合(ATRP)的引发剂2-溴异丁酸乙酯(EbiB),2-溴丙酸甲酯(MBP),二氯化苄(DCT)在氯化铜/五甲基二乙烯三胺,氯化铁/五(丙烯酸甲酯)二乙烯三胺等高价态过渡金属卤化物/络合剂的存在下也可以引发甲基丙烯酸甲酯的聚合,所得聚合物分子量分布较窄(1.10~1.20),反应具有较好的可控性。本文讨论了不同高价态过渡金属催化剂/络合剂以及聚合温度对反应的影响并深入探讨了反应机理。     

ATRP引发剂的非正常引发

通常只能与低价过渡金属卤化物/络合剂配合才能引发原子转移自由基聚合(ATRP)的引发剂2-溴异丁酸乙酯(EbiB),2-溴丙酸甲酯(MBP),二氯化苄(DCT)在氯化铜/五甲基二乙烯三胺,氯化铁/五(丙烯酸甲酯)二乙烯三胺等高价态过渡金属卤化物/络合剂的存在下也可以引发甲基丙烯酸甲酯的聚合,所得聚合物分子量分布较窄(1.10~1.20),反应具有较好的可控性。本文讨论了不同高价态过渡金属催化剂/络合剂以及聚合温度对反应的影响并深入探讨了反应机理。     

原子转移自由基聚合及催化剂负载化研究进展

原子转移自由基聚合(ATRP)具有可控聚合的典型特征,自1995年来受到高分子界的广泛关注。介绍了ATRP在应用方面的研究进展;传统ATRP由于存在催化剂脱除困难等问题,制约了其工业化进程。介绍了易分离的负载型催化剂的近期研究进展。     

电子转移活化再生催化剂原子转移自由基聚合(ARGET ATRP)的研究进展

ARGET ATRP可将反应中催化剂用量降至ppm级,是目前最具工业化应用前景的原子转移自由基聚合(ATRP)之一。综述了ARGET ATRP的反应机理、引发剂、催化体系、还原剂、反应条件及其在污水处理、纤维素改性、燃料电池方面的应用,并对ARGET ATRP技术的前景进行了展望。     

细菌纤维素气凝胶ARGET ATRP接枝聚甲基丙烯酸缩水甘油酯EI北大核心CSCD

以含溴的细菌纤维素气凝胶为引发剂,维生素C(Vc)为还原剂,N,N,N',N,'N″-五甲基二亚乙基三胺(PMDETA)/溴化铜(Cu Br2)为催化剂,通过电子转移活化再生催化剂原子转移自由基聚合(ARGET ATRP)方法,制备了含聚甲基丙烯酸缩水甘油酯(PGMA)刷的细菌纤维素气凝胶规整接枝共聚物。采用能谱对大分子引发剂元素含量进行测定,并利用红外光谱、X射线衍射、扫描电镜、热失重分析对其结构和性能进行表征。结果表明,接枝聚合反应可控,大分子引发剂Br元素含量为6.77%;GMA接枝聚合后纤维直径增大且在纤维表面形成覆盖层;起始热分解温度由205℃升高到246℃,热稳定性增强。     

以PMDETA为配体的甲基丙烯酸丁酯ARGET ATRP研究

以廉价配体五甲基二乙烯三胺(PMDETA)、溴化铜(CuBr2)和还原剂为催化体系,进行了甲基丙烯酸丁酯(BMA)的电子转移再生活化剂原子转移自由基聚合研究(ARGET ATRP),考察了影响反应可控性的因素。实验结果表明,配体用量至少为催化剂量10倍(物质的量)以上,反应温度应在65℃～85℃,所得聚合物分子量分布较窄;还原剂用量增加,反应速率变快,但分子量分布变宽;催化剂用量减少时,还原剂相对用量要增加;催化剂的最少用量取决于引发剂与催化剂的物质的量比,当引发剂和催化剂物质的量比小于1:0.02时,催化剂的用量能降到单体物质的量的5×10-5倍,仍保持可控聚合,所得聚合物分子量分布较窄为1.29。     

Use of Yb-based catalyst for AGET ATRP of acrylonitrile to simultaneously control molecular mass distribution and tacticity

Yb-based catalyst was used for the first time for atom transfer radical polymerization using activators generated by electron transfer (AGET ATRP) of acrylonitrile (AN) with 2-bromopropionitrile (BPN) as initiator, 2, 2′-bipyridine (bipy) as ligand, and tisn(II) bis(2-ethylhexanoate) (Sn(EH)₂) as reducing agent in the presence of air. With respect to AGET ATRP of AN catalyzed by CuBr₂, an evident increase of polymer tacticity was observed for AGET ATRP of AN. The increase of syndiotacticity became more and more pronounced than the increase of isotacticity of polyacrylonitrile (PAN) along with YbBr₃ content. The block copolymer PAN-b-PMMA with molecular weight at 60,000 and polydispersity at 1.36 was successfully prepared.     

Synthesis of polyacrylonitrile-grafted cross-linked N-chlorosulfonamidated polystyrene via surface-initiated ARGET ATRP, and use of the resin in mercury removal after modification

A novel method of surface modification was developed via iron (III)-mediated atom transfer radical polymerization, with activators regenerated by electron transfer (ARGET ATRP) on the surfaces of polystyrene resin-supported N-chlorosulfonamide groups. The well-defined polyacrylonitrile (PAN) was grafted onto the surfaces of the polystyrene (PS). The graft reaction exhibited first-order kinetics with respect to the polymerization time in the low-monomer-conversion stage. The cyano group of PAN-g-PS was modified by NH(2)OH·HCl to yield amidoxime (AO) groups. The AO groups had been demonstrated to be an efficient Hg-specific sorbent, which can remove Hg(2+) from solutions. No interference arose from common metal ions, such as Pd(2+), Ag(+), and Cu(2+). Three adsorption-desorption cycles demonstrated that this resin is suitable for reuse without any considerable change in adsorption capacity.     

Use of 1-alkyl-3-methylimidazolium l-lactates as both ligand and reaction media for AGET ATRP of acrylonitrile

Chiral ionic liquids, [C₂mim][LLA], [C₄mim][LLA] and [C₆mim][LLA] were firstly applied as both ligand and reaction media for atom transfer radical polymerization using activators generated by electron transfer (AGET ATRP) of acrylonitrile (AN) with ascorbic acid (VC) as reducing agent in the presence of air. A small but clear increase of polyacrylonitrile (PAN) isotacticity was observed for AGET ATRP of AN in [C₆mim][LLA] than in [C₆mim][BF₄]. PAN isotacticity markedly increased with the content of [C₆mim][LLA]. Compared with in [C₂mim][LLA] and [C₄mim][LLA], the rate of AGET ATRP of AN in [C₆mim][LLA] was fastest and the polymerization was best controlled. Well-defined PAN with molecular weight at 76,590, relatively narrower distribution at 1.27 and higher isotacticity at 0.37 was successfully prepared in [C₆mim][LLA].     

Synthesis of densely grafted copolymers with tert-butyl methacrylate/2-(dimethylamino ethyl) methacrylate side chains as precursors for brush polyelectrolytes and polyampholytes

Methacrylate-based densely grafted copolymers were synthesized by atom transfer radical polymerization (ATRP) and activators generated by electron transfer for atom transfer radical polymerization (AGET ATRP) techniques. The linear poly(2-(2-bromoisobutyryloxy)ethyl methacrylate) PBIEM prepared by ATRP served as a macroinitiator backbone. The “grafting from” strategy was used to initiate polymerization of tert-butyl methacrylate (tBuMA) from PBIEM under ATRP and/or AGET ATRP conditions yielding densely grafted copolymers PBIEM-graft-P(tBuMA). The low polydispersity indices (PDI) of the synthesized brushes evidenced by SEC analysis were consistent with a controlled/living radical polymerization (CLRP) mechanism. The chlorine-terminated PBIEM-graft-P(tBuMA)-Cl macroinitiators were subsequently employed for chain extension with 2-(dimethylamino ethyl) methacrylate (DMAEMA) yielding densely grafted copolymers with diblock copolymer side chains PBIEM-graft-P(tBuMA)-block-PDMAEMA. Further, PBIEM macroinitiator was used to initiate the copolymerization of a binary mixture of tBuMA and DMAEMA through both ATRP and AGET ATRP initiating systems, yielding densely grafted copolymers with statistical distribution of the side chains. The reactivity ratios for random graft copolymerization of tBuMA and DMAEMA from PBIEM backbone established by three different methods (Finemann-Ross, Kelen-Tüdös and Error-in-Variable) did not substantially differ from literature values for conventional free-radical copolymerization of the same monomers. Polyampholyte brushes with PMAA-stat-PDMAEMA side chains were eventually synthesized by hydrolysis of the shielding tert-butyl groups.     

ATRP-based synthesis and characterization of light-responsive coatings for transdermal delivery systems

Abstract

The grafting of poly(hydroxyethylmethacrylate) on polymeric porous membranes via atom transfer radical polymerization (ATRP) and subsequent modification with a photo-responsive spiropyran derivative is described. This method leads to photo-responsive membranes with desirable properties such as light-controlled permeability changes, exceptional photo-stability and repeatability of the photo-responsive switching. Conventional track etched polyester membranes were first treated with plasma polymer coating introducing anchoring groups, which allowed the attachment of ATRP-initiator molecules on the membrane surface. Surface initiated ARGET–ATRP of hydroxyethylmethacrylate (where ARGET stands for activator regenerated by electron transfer) leads to a membrane covered with a polymer layer, whereas the controlled polymerization procedure allows good control over the thickness of the polymer layer in respect to the polymerization conditions. Therefore, the final permeability of the membranes could be tailored by choice of pore diameter of the initial membranes, applied monomer concentration or polymerization time. Moreover a remarkable switch in permeability (more than 1000%) upon irradiation with UV-light could be achieved. These properties enable possible applications in the field of transdermal drug delivery, filtration, or sensing.     

ATRP-based synthesis and characterization of light-responsive coatings for transdermal delivery systems

The grafting of poly(hydroxyethylmethacrylate) on polymeric porous membranes via atom transfer radical polymerization (ATRP) and subsequent modification with a photo-responsive spiropyran derivative is described. This method leads to photo-responsive membranes with desirable properties such as light-controlled permeability changes, exceptional photo-stability and repeatability of the photo-responsive switching. Conventional track etched polyester membranes were first treated with plasma polymer coating introducing anchoring groups, which allowed the attachment of ATRP-initiator molecules on the membrane surface. Surface initiated ARGET–ATRP of hydroxyethylmethacrylate (where ARGET stands for activator regenerated by electron transfer) leads to a membrane covered with a polymer layer, whereas the controlled polymerization procedure allows good control over the thickness of the polymer layer in respect to the polymerization conditions. Therefore, the final permeability of the membranes could be tailored by choice of pore diameter of the initial membranes, applied monomer concentration or polymerization time. Moreover a remarkable switch in permeability (more than 1000%) upon irradiation with UV-light could be achieved. These properties enable possible applications in the field of transdermal drug delivery, filtration, or sensing.     

竹粉接枝改性及其对竹粉/PETG复合材料流变行为的影响

采用电子活化再生原子转移自由基聚合（AGET ATRP）法将甲基丙烯酸甲酯（MMA）接枝到竹粉（BF）表面,并采用哈克微量混合流变仪及旋转流变仪考察了竹粉接枝改性前后对竹粉/聚对苯二甲酸乙二醇酯-1,4-环己烷二甲醇酯（PETG）复合材料流变行为的影响。毛细管流变结果表明,竹粉/PETG复合材料属于假塑性流体,呈现剪切变稀的现象;应变扫描结果表明,与未改性竹粉/PETG复合材料体系相比,竹粉经接枝改性后其复合材料体系在更大的应变范围内属于线性弹性行为;频率扫描结果表明,竹粉的接枝改性处理有助于促进竹粉在PETG基体中的均匀分散。     

AGET ATRP of acrylonitrile with ionic liquids as reaction medium without any additional ligand

Atom transfer radical polymerization using activators generated by electron transfer (AGET ATRP) of acrylonitrile (AN) was carried out for the first time in 1-methylimidazolium acetate ([mim][AT]), 1-methylimidazolium propionate([mim][PT]), and 1-methylimidazolium butyrate ([mim][BT]), respectively. The polymerization was approached by using ascorbic acid (VC) as a reducing agent, ethyl 2-bromoisobutyrate (EBiB) as initiator, only FeBr₃ as catalyst without any additional ligand. Kinetic studies showed that both AGET ATRP of AN in the absence of oxygen and in the presence of air proceeded in a well-controlled manner. Under the same conditions, the polymerization in the presence of air provided rather slower reaction rate and showed better control of molecular weight and its distribution than in the absence of oxygen. The sequence of the apparent polymerization rate constants of AGET ATRP of AN in three ionic liquids was k_app([mim][AT]) > k_app([mim][PT]) > k_app([mim][BT]). The living nature of the polymerization was confirmed by chain end analysis and block copolymerization of methyl methacrylate with polyacrylonitrile as macroinitiator. All the three ionic liquids and FeBr₃ could be recycled and reused and had no effect on the living nature of polymerization.     

ATRP表面接枝在功能膜制备中的应用

ATRP表面引发接枝聚合是功能膜制备中一个重要而有效的方法.近年来,随着原子转移自由基聚合(ATRP)研究的快速发展,将ATRP应用于功能膜制备的研究已取得了显著的进展.详细介绍了在膜表面固定ATRP引发剂的方法及将ATRP表面接枝法应用于制备抗污染能力强,抗菌性好,环境响应迅速等多种功能性膜方面的研究进展情况.