Facile Soap‐Free Miniemulsion Polymerization of Methyl Methacrylate via Reverse Atom Transfer Radical Polymerization

A facile soap‐free miniemulsion polymerization of methyl methacrylate (MMA) was successfully carried out via a reverse ATRP technique, using a water‐soluble potassium persulfate (KPS) or 2,2′‐azobis(2‐methylpropionamidine) dihydrochloride (V‐50) both as the initiator and the stabilizer, and using an oil‐soluble N,N‐n‐butyldithiocarbamate copper (Cu(S₂CN(C₄H₉)₂)₂) as the catalyst without adding any additional ligand. Polymerization results demonstrated the “living”/controlled characteristics of ATRP and the resultant latexes showed good colloidal stability with average particle size around 300–700 nm in diameter. The monomer droplet nucleation mechanism was proposed. NMR spectroscopy and chain‐extension experiments under UV light irradiation confirmed the attachment and livingness of UV light sensitive  S C(S) N(C₄H₉)₂ group in the chain end.     

Diffusion‐Regulated Phase‐Transfer Catalysis for Atom Transfer Radical Polymerization of Methyl Methacrylate in an Aqueous/Organic Biphasic System

A concept based on diffusion‐regulated phase‐transfer catalysis (DRPTC) in an aqueous‐organic biphasic system with copper‐mediated initiators for continuous activator regeneration is successfully developed for atom transfer radical polymerization (ICAR ATRP) (termed DRPTC‐based ICAR ATRP here), using methyl methacrylate (MMA) as a model monomer, ethyl α‐bromophenylacetate (EBrPA) as an initiator, and tris(2‐pyridylmethyl)amine (TPMA) as a ligand. In this system, the monomer and initiating species in toluene (organic phase) and the catalyst complexes in water (aqueous phase) are simply mixed under stirring at room temperature. The trace catalyst complexes transfer into the organic phase via diffusion to trigger ICAR ATRP of MMA with ppm level catalyst content once the system is heated to the polymerization temperature (75 °C). It is found that well‐defined PMMA with controlled molecular weights and narrow molecular weight distributions can be obtained easily. Furthermore, the polymerization can be conducted in the presence of limited amounts of air without using tedious degassed procedures. After cooling to room temperature, the upper organic phase is decanted and the lower aqueous phase is reused for another 10 recycling turnovers with ultra low loss of catalyst and ligand loading. At the same time, all the recycled catalyst complexes retain nearly perfect catalytic activity and controllability, indicating a facile and economical strategy for catalyst removal and recycling.

     

Phosphorus Ligands for Iron(III)‐Mediated Atom Transfer Radical Polymerization of Methyl Methacrylate

The iron(III)‐catalyzed atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) was successfully employed using tributylphosphine (TBP) and trimethylphosphite (TMP) as ligands in the absence of a reducing agent. The effects of solvent and initiator on polymerization of MMA were investigated. Most of the polymerizations with these ligands were well controlled with a linear increase in the number average molecular weights ( ) versus conversion and relatively low molecular weight distribution ( = 1.2–1.4) throughout the reactions, and the measured weights matched with the predicted values. The ethyl 2‐bromoisobutyrate (EBriB) initiated ATRP of MMA with the FeBr₃/TBP or FeBr₃/TMP catalytic system was better controlled in toluene than in the other solvents used in this study at 80 °C.

     

Uniform PEO Star Polymers Synthesized in Water via Free Radical Polymerization or Atom Transfer Radical Polymerization

Amphiphilic star shaped polymers with poly(ethylene oxide) (PEO) arms and cross‐linked hydrophobic core were synthesized in water via either conventional free radical polymerization (FRP) or atom transfer radical polymerization (ATRP) techniques using a simple “arm‐first” method. In FRP, PEO based macromonomers (MM) were used as arm precursors, which were then cross‐linked by divinylbenzene (DVB) using 2,2′‐azoisobutyronitrile (AIBN). Uniform star polymers ( < 1.2) were achieved through adjustment of the ratio of PEO MM, DVB, and AIBN. While in case of ATRP, both PEO MM, and PEO based macroinitiator (MI) were used as arm precursors with ethylene glycol diacrylate as cross‐linker. Even more uniform star polymers with less contamination by low MW polymers were obtained, as compared to the products synthesized by FRP.

     

Atom Transfer Radical Polymerization of Styrene and Methyl Methacrylate from Mesoporous Ordered Silica Particles

Summary: Mesoporous silica was used as substrate for the grafting of alkyl halides initiators. The control over the surface‐initiated polymerization of styrene and MMA, in terms of molar mass and molar mass distribution, was successfully achieved using an ATRP mechanism. The occurrence of the polymerization inside the mesopores was confirmed by thermogravimetric analysis.

Transmission electron microscopy and schematic representation of mesoporous silica functionalized by the anchored iniator (left) and the grafted polymer (right).     

Atom Transfer Radical Polymerization of N,N‐Dimethylacrylamide

Summary: The living polymerization of N,N‐dimethylacrylamide was achieved by atom transfer radical polymerization catalyzed by copper chloride complexed with a new ligand, N,N′‐bis(pyridin‐2‐ylmethyl 3‐hexoxo‐3‐oxopropyl)ethane‐1,2‐diamine (BPED). With methyl 2‐chloropropionate as the initiator, the polymerization reached high conversions (> 90%) at 80 °C and 100 °C, producing polymers with very close to theoretical values and low polydispersity. The ligand, temperature, and copper halide strongly affected the activity and control of the polymerization.

PDMA molecular weight and polydispersity dependence on the DMA conversion in the DMA bulk polymerizations at different temperatures: DMA/CuCl/MCP/BPED = 100/1/1/1, 100 °C (♦, ⋄); 80 °C (▴, ▵); 60 °C (▪, □); and DMA/CuCl/MCP/BPED = 100/1/1/2, 80 °C (•, ○).     

Atom Transfer Radical Polymerization of N‐Isopropylacrylamide

Summary: Controlled polymerization of N‐isopropylacrylamide (NIPAAM) was achieved by atom transfer radical polymerization (ATRP) using ethyl 2‐chloropropionate (ECP) as initiator and CuCl/tris(2‐dimethylaminoethyl)amine (Me₆TREN) as a catalytic system. The polymerization was carried out in DMF:water 50:50 (v/v) mixed solvent at 20 °C. The first order kinetic plot was linear up to 92% conversion. Controlled molecular weights up to 2.2 × 10⁴ and low polydispersities (1.19) were obtained. The living character of the polymerization was also demonstrated by self‐blocking experiments. Block copolymers with N,N‐dimethylacrylamide (DMAAM) and 3‐sulfopropyl methacrylate (SPMA) were successfully prepared.

Molecular weights and polydispersities of polyNIPAAM versus NIPAAM conversion for two different degrees of polymerization.     

Highly Active ppm Level Organic Copper Catalyzed Photo‐Induced ICAR ATRP of Methyl Methacrylate

A novel photo‐induced homogeneous atom transfer radical polymerization (ATRP) system is constructed using an organic copper salt (Cu(SC(S)N(C₂H₅)₂)₂) as a photo‐induced catalyst at 30 °C. Herein, N,N,N′,N′′,N′′‐pentamethyldiethylenetriamine (PMDETA) is used as a ligand, ethyl 2‐bromophenylacetate (EBPA) as an ATRP initiator, and (2,4,6‐trimethylbenzoyl) diphenylphosphine oxide (TPO) as a photo‐induced radical initiator to establish an ICAR (initiators for continuous activator regeneration) ATRP using methyl methacrylate (MMA) as a modal monomer. The effect of the concentration of the organic copper on the polymerization is investigated in detail. It is found that well‐controlled polymerization can be obtained even with the amount of (Cu(SC(S)N(C₂H₅)₂)₂ decreasing to a 1.56 ppm level, with the molecular weight of the resultant polymers increasing linearly with monomer conversion while maintaining a narrow molecular weight distribution (/ < 1.3).

     

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。     

酚氧基联烯基醚单体的原子转移自由基聚合研究

以具有较高活性的酚氧基联烯基醚(POA)和对叔丁基酚氧基联烯基醚(t-BuPOA)为研究对象, 研究了不同引发 剂/配体体系对其原子转移自由基(ATRP)聚合行为的影响. 发现在2-溴代丙酸甲酯/溴化亚铜/4,4’-二庚基联吡啶(2-MBP/CuBr/dHbpy)和对甲苯磺酰氯/溴化亚铜/三-(N,N-二甲基氨基乙基)胺(p-TsCl/CuBr/Me6TREN)两种ATRP反应体系中, POA的聚合都遵循ATRP反应的机理.     

Atom Transfer Radical Polymerization of iso‐Butyl Methacrylate in Microemulsion with Cationic and Non‐Ionic Emulsifiers

Direct atom transfer radical polymerization (ATRP) of iso‐butyl methacrylate in microemulsion has been performed successfully for the first time. ATRP was performed at 40 °C with different emulsifier systems: i) the cationic emulsifier n‐tetradecyltrimethylammonium bromide (TTAB); and ii) mixed emulsifier systems based on TTAB and the non‐ionic emulsifiers Emulgen 911 or Emulgen 931. All polymerizations proceeded in a controlled/living fashion, and the microemulsions were transparent with particle diameters less than 15 nm. The emulsifier system TTAB/Emulgen 911 exhibited better control than TTAB only. This is proposed to be caused by complex formation between Emulgen 911 in the organic phase and CuBr₂ (the deactivator), thus reducing the extent of exit of CuBr₂ to the aqueous phase. The more hydrophilic Emulgen 931 did not lead to improved control.

     

有机催化原子转移自由基聚合

过渡金属催化的原子转移自由基聚合(ATRP)是合成结构可控聚合物的重要方法之一,尽管一系列改进ATRP方法可将催化剂的浓度降至ppm级,但不可避免的金属残留仍然是制约ATRP应用的主要瓶颈。近年来,科学家提出并发展了有机催化原子转移自由基聚合(O-ATRP),从根本上规避了金属催化剂的使用与残留。本文对有机催化原子转移自由基聚合的概念、催化体系和聚合机理进行了介绍,同时综述了该新聚合方法在高分子合成与材料制备方面的应用。     

Heterogeneity Features of Bulk Atom Transfer Radical Polymerization of Methyl Methacrylate in an Ampoule Reactor

Summary: This work demonstrated the severity of heterogeneity issues with ampoule reactors in bulk atom transfer radical polymerization of methyl methacrylate. The kinetic data of Cu^II concentration, monomer conversion, and polymer molecular weight varied from location to location along the ampoule. However, the polymer molecular weight versus conversion data from different locations fell into a single theoretical line. All locations except for the bottom part of the ampoule produced polymers having narrow molecular weight distribution.

Conversion versus time at different locations for the ATRP of MMA at 70 °C.     

Atom Transfer Radical Polymerization of Methyl Methacrylate High Efficiently Initiated by Azo-containing Iniferter

Two novel azo-containing iniferters, (4,4′-(diazene-1,2-diyl) bis(4,1-phenylene) bis(2-(diethylca-rbamothioylthio)-2-methylpropanoate (BDCMP) and 4-((4-bromophenyl)diazenyl)phenyl-2-(diethylcarbamothioylthio)-2-methylpropanoate (PDCMP) were synthesized and used successfully as the initiators for atom transfer radical polymerization of methyl methacrylate (MMA). The kinetic plots were first order and the molecular weights of the polymers with narrow molecular weight distributions increased with the monomer conversions. Furthermore, the results showed that the apparent initiation efficiencies (f was close to 0.90 defined as M _n(th)/M _n(GPC)) of BDCMP and PDCMP were both higher than that (f was lower than 0.5) of 2-N,N-(diethylamino)dithiocarboyl-isobutyrate (EDCIB), which was reported previously by us (14 Zhang, W., Zhu, X. L., Cheng, Z. P. and Zhu, J. 2007. J. Appl. Polym. Sci., 106: 230–7. [Crossref] , [Google Scholar]). The obtained mono- and bi-functional PMMAs containing azo and N,N-diethyldithiocarbamate (DC) groups were confirmed by ¹H-NMR and ultraviolet absorption spectra, respectively. The block copolymer, poly (methyl methacrylate)-b-polystyrene (PMMA-b-PS), was also successfully prepared via the ATRP chain-extension experiment using the obtained PMMA as a macroinitiator.     

Monomode Microwave‐Assisted Atom Transfer Radical Polymerization

Summary: The first monomode microwave‐assisted atom transfer radical polymerization (ATRP) is reported. The ATRP of methyl methacrylate was successfully performed with microwave heating, which was well controlled and provided almost the same results as experiments with conventional heating, demonstrating the absence of any “microwave effect” in ATRP (in contrast to several literature reports). Furthermore, we found that the main advantage of the microwave‐assisted reactions over conventional reactions, i.e., a significant increase of reaction rates, only had its limited application in ATRP, even in very slow ATRP systems with high targeted molecular weights.

Comparison of the kinetic plots of the ATRP of MMA ([MMA]₀/[EBIB]₀/[CuCl]₀/[NHPMI]₀ = 200:1:1:3, MMA/DMF = 1:1 v/v) carried out at 90 °C in DMF with microwave (▴) and conventional heating (•), respectively.     

室温下甲基丙烯酸甲酯原子转移自由基乳液聚合反应研究

以卤化亚铜（CuX）/1,10-邻二氮菲（phen）配合物为催化剂、2-溴代异丁酸 乙酯（EBiB）为引发剂、十二烷基磺酸钠（SLS）为乳化剂,进行了甲基丙烯酸甲 酯（MMA）的原子转移自由基乳液聚合（ATRP）反应。结果表明,与较高温度（70 - 90 ℃）下的聚合反应相比,室温（25 ℃）时聚合反应有更好的可控性,通过 外加钝化剂的复合催化引发体系CuBr/CuBr_2/phen/EBiB或利用CuCl/phen/EBiB催 化引发体系的“卤素交换反应”,可进一步改善聚合反应的可控性。紫外发光谱测 定结果表明,CuBr/phen配合物在MMA相中的分配倾向随着温度的降低而增大,使得 室温下MMA的乳液ATRP保持了较好的可控性和较快的反应速度。     

Synthesis of Block Copolymers by Combination of Atom Transfer Radical Polymerization and Visible Light‐Induced Free Radical Promoted Cationic Polymerization

A new synthetic approach for the preparation of block copolymers by mechanistic transformation from atom transfer radical polymerization (ATRP) to visible light‐induced free radical promoted cationic polymerization is described. A series of halide end‐functionalized polystyrenes with different molecular weights synthesized by ATRP were utilized as macro‐coinitiators in dimanganese decacarbonyl [Mn₂(CO)₁₀] mediated free radical promoted cationic photopolymerization of cyclohexene oxide or isobutyl vinyl ether. Precursor polymers and corresponding block copolymers were characterized by spectral, chromatographic, and thermal analyses.     

Filling Polymersomes with Polymers by Peroxidase‐Catalyzed Atom Transfer Radical Polymerization

Polymersomes that encapsulate a hydrophilic polymer are prepared by conducting biocatalytic atom transfer radical polymerization (ATRP) in these hollow nanostructures. To this end, ATRPase horseradish peroxidase (HRP) is encapsulated into vesicles self‐assembled from poly(dimethylsiloxane)‐block‐poly(2‐methyl‐2‐oxazoline) (PDMS‐b‐PMOXA) diblock copolymers. The vesicles are turned into nanoreactors by UV‐induced permeabilization with a hydroxyalkyl phenone and used to polymerize poly(ethylene glycol) methyl ether acrylate (PEGA) by enzyme‐catalyzed ATRP. As the membrane of the polymersomes is only permeable for the reagents of ATRP but not for macromolecules, the polymerization occurs inside of the vesicles and fills the polymersomes with poly(PEGA), as evidenced by ¹H NMR. Dynamic and static light scattering show that the vesicles transform from hollow spheres to filled spheres during polymerization. Transmission electron microscopy (TEM) and cryo‐TEM imaging reveal that the polymersomes are stable under the reaction conditions. The polymer‐filled nanoreactors mimic the membrane and cytosol of cells and can be useful tools to study enzymatic behavior in crowded macromolecular environments.