Heteroatom‐Doped Carbon Dots (CDs) as a Class of Metal‐Free Photocatalysts for PET‐RAFT Polymerization under Visible Light and Sunlight

A key challenge of photoregulated living radical polymerization is developing efficient and robust photocatalysts. Now carbon dots (CDs) have been exploited for the first time as metal‐free photocatalysts for visible‐light‐regulated reversible addition–fragmentation chain‐transfer (RAFT) polymerization. Screening of diverse heteroatom‐doped CDs suggested that the P‐ and S‐doped CDs were effective photocatalysts for RAFT polymerization under mild visible light following a photoinduced electron transfer (PET) involved oxidative quenching mechanism. PET‐RAFT polymerization of various monomers with temporal control, narrow dispersity (?≈1.04), and chain‐end fidelity was achieved. Besides, it was demonstrated that the CD‐catalyzed PET‐RAFT polymerization was effectively performed under natural solar irradiation.     

Dimethyl Dihydroacridines as Photocatalysts in Organocatalyzed Atom Transfer Radical Polymerization of Acrylate Monomers

Development of photocatalysts (PCs) with diverse properties has been essential in the advancement of organocatalyzed atom transfer radical polymerization (O‐ATRP). Dimethyl dihydroacridines are presented here as a new family of organic PCs, for the first time enabling controlled polymerization of challenging acrylate monomers by O‐ATRP. Structure–property relationships for seven PCs are established, demonstrating tunable photochemical and electrochemical properties, and accessing a strongly oxidizing ²PC^.+ intermediate for efficient deactivation. In O‐ATRP, the combination of PC, implementation of continuous‐flow reactors, and promotion of deactivation through addition of LiBr are critical to producing well‐defined acrylate polymers with dispersities as low as 1.12. The utility of this approach is established through demonstration of the oxygen‐tolerance of the system and application to diverse acrylate monomers, including the synthesis of well‐defined di‐ and triblock copolymers.     

Controlled Radical Polymerization of Furfuryl Methacrylate

Atom transfer radical polymerization provides a new method of controlled radical polymerization. The most important advantage of ATRP is that it is tolerant to the different functional groups present in the initiator as well as in the monomer. Furfuryl Methacrylate (FMA) is a specialty monomer, which has applications in coatings, adhesives and in biomedicals. Conventional radical polymerization of FMA leads to excessive gel formation, which limits its applications. In this investigation homo and co-polymerization of FMA has been carried out via ATRP. ATRP of FMA was carried out using CuBr as catalyst and 1, 1, 4, 7, 10, 10 hexamethyltriethylenetetramine (HMTETA) as ligand. There was no gel formation during the polymerization. ATRP of FMA was well controlled with a linear increase of molecular weight (Mn) with monomer conversion. The polymers were characterized by using ¹HNMR, FT-IR and GPC analysis. Interestingly, it was observed that the furfuryl ring was not affected during polymerization.     

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.     

Atom Transfer Radical Polymerization of MMA Initiated by 2‐(4‐chloromethyl‐phenyl)‐benzoxazole and Fluorescent Property of PMMA

Atom transfer radical polymerization (ATRP) of MMA was conducted using 2‐(4‐chloromethyl‐phenyl)‐benzoxazole as initiator, CuCl as catalyst, and PMDETA as ligand. The results show that the polymerization is a first order reaction with respect to monomer concentration. The polymerization displayed living character as evidenced by a liner increase of monomer weight with conversation and a relatively narrow distribution (Mn/Mw range from 1.30 to 1.45). The structure of PMMA was analyzed by ¹H‐NMR and proved the polymerization could be controlled to some degree. The optical property of the initiator was well preserved in the resulting PMMA, and the end‐functionalized PMMA exhibited fluorescent emission at 360 nm whether in DMF solution or in film state.     

原子转移自由基聚合法制备超大孔聚合物微球

以甲基丙烯酸缩水甘油酯为单体(GMA)、乙二醇二甲基丙烯酸酯(EDMA)为交联剂,采用原子转移自由基聚合法(ATRP)制备了PGMA-EDMA大孔聚合物微球,采用傅里叶变换红外光谱、扫描电子显微镜及压汞法对PGMA-EDMA微球进行了表征.研究结果表明,原子转移自由基聚合法制备的PGMA-EDMA微球的孔径尺寸及比表面积均大于普通自由基聚合法(CFRP)制备的PGMA-EDMA;ATRP法制备的PGMAEDMA微球的颗粒尺寸(100~400 nm)明显小于CFRP法制备的PGMA-EDMA微球的颗粒尺寸(1000 nm).PGMA-EDMA(ATRP)的微球粒径尺寸分布优于PGMA-EDMA(CFRP).因此PGMA-EDMA(APRP)微球在快速蛋白分离纯化方面有潜在的应用前景.     

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.     

Near‐Infrared Sensitized Photoinduced Atom‐Transfer Radical Polymerization (ATRP) with a Copper(II) Catalyst Concentration in the ppm Range

NIR‐sensitized photoinduced atom‐transfer radical polymerization (ATRP) is possible by using ppm of Cu^II/tris(2‐pyridylmethyl)amine (TPMA) as the catalyst, a polymethine as the photosensitizer, and α‐bromophenylacetate as the alkyl halide initiator. Among the polymethines investigated with cationic, zwitterionic, or anionic structures, only the zwitterionic 2 exhibited sensitization activity under NIR light at room temperature resulting in the formation of polymers with controlled molecular weight characteristics and functionalities. The barbital group placed at the meso‐position of 2 caused the activity in this photo‐ATRP framework. The chain‐end fidelity of the polymers was confirmed by chain extension and block copolymerization experiments. The polymerization system exhibits high photostability under NIR light exposure and irradiation dependency as demonstrated by light on/off experiments.     

Solid‐State Carbon Dots with Efficient Cyan Emission towards White Light‐Emitting Diodes

Efficient cyan‐emitting solid carbon dots (CDs) were synthesized via a one‐pot hydrothermal method. The obtained solid CDs show a broad absorption from 270–460 nm with a maximum around 400 nm, and emit intense cyan light around 500 nm with an internal photoluminescence quantum efficiency of 34.1 % under 400 nm excitation. The emission maximum of the solid CDs remains unchanged under 320–400 nm excitations. Compared with dilute aqueous of CDs (2.5 mg mL^?1), the emission of solid CDs shows an obvious red‐shift of 50 nm. The red‐shift is caused by resonant energy transfer due to larger spectral overlap and smaller interparticle distance, together with a new surface state caused by aggregation in solid CDs. A lamp with white LEDs was fabricated by dropping a mixture of solid CDs, CaAlSiN₃:Eu²⁺ and silicon resin on the top of a near‐ultraviolet LED chip. Under an operating current of 20 mA, the as‐fabricated white LED generates a high‐quality, warm white light with a color rendering index of 86.1, a color temperature of 4340 K, and a luminescence efficiency of 31.3 lm W^?1.     

Benzyl Bromide Functionalized Poly(Phenyleneethynylene)s as Macroinitiators in the Atom Transfer Radical Polymerization of Methyl Methacrylate

Abstract

The behavior of benzyl bromide functionalized poly(phenyleneethynylene)s as macroinitiators in the atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) was investigated. The ¹H NMR observation of the ATRP using the exclusively para‐linked poly(phenyleneethynylene) macroinitiator PPE1A, and the low molecular weight initiator R‐BzBr, respectively, revealed lower reactivity for the macroinitiator. Comparison of graft copolymers, which were obtained from ATRP of MMA with PPE1A and the partially meta‐linked poly(phenyleneethynylene) PPE1B, showed higher reactivity in the case of PPE1B, expressed by a larger degree of polymerization in the PMMA side chains, as well as higher initiatior efficiency. This might be caused by better solubility of the less symmetric PPE1B. Investigation of the graft copolymers PPE2A and PPE2B was carried out by means of ¹H NMR spectroscopy, gel permeation chromatography (GPC) as well as UV/vis spectroscopy. Impairment of the delocalized π‐electron system of the conjugated polymers during the ATRP was not detectable.     

Visualization of Atom Transfer Radical Polymerization by Aggregation‐Induced Emission Technology

Aggregation‐induced emission (AIE) technology has been demonstrated to be a facile approach for in‐situ monitoring atom transfer radical polymerization (ATRP). A series of tertraphenyl ethylene (TPE)‐containing α‐bromo compounds were synthesized and applied as ATRP initiators. The photoluminescent (PL) emission of the polymerization system is proved to be sensitive to the local viscosity owing to the AIE characteristics of TPE. Linear relationships between the resulting molecular weight M_n and PL intensity were observed in several polymerization systems with different monomers, indicating the variability of this technique. Compared to physical blending, the chemical bonding of the TPE group in the chain end has higher sensitivity and accuracy to the polymer segments and the surrounding environment. This work promoted the combination of the AIE technique and controlled living radical polymerization, and introduced such an optical research platform to the ATRP polymerization process.     

Competitive Equilibria in Atom Transfer Radical Polymerization

With the recent development of new initiation techniques in atom transfer radical polymerization (ATRP) that allow catalysts to be employed at unprecedented low concentrations (∼10 ppm), a thorough understanding of competitive equilibria that can affect catalyst performance is becoming increasingly important. Such mechanistic considerations are discussed herein, including i) factors affecting the position of the ATRP equilibrium; ii) dissociation of the ATRP catalyst at high dilution and loss of deactivator due to halide dissociation; iii) conditional stability constants as related to competitive monomer, solvent, and reducing agent complexation as well as ligand selection with respect to protonation in acidic media; and iv) competitive equilibria involving electron transfer reactions, including the radical oxidation to carbocations or reduction to carbanions, radical coordination to the metal catalyst, and disproportionation of the Cu^I-based ATRP activator.     

Synthesis of diblock copolymers by combination of organocatalyzed ring‐opening polymerization and atom transfer radical polymerization using trichloroethanol as a bifunctional initiator

This study reports an application of trichloroethanol (TCE) as a bifunctional initiator for the synthesis of block copolymers (BCPs) by organocatalyzed ring‐opening polymerization (OROP) and atom transfer radical polymerization (ATRP). TCE was employed to synthesize a low dispersity poly (valerolactone) macroinitiator, which was subsequently used for the ATRP of tert‐butyl methacrylate. While it is known that TCE can serve as an initiator in ATRP, the ability to induce polymerization under OROP is reported for the first time. The formation of well‐defined BCPs was confirmed by gel permeation chromatography and ¹H NMR. Computational studies were performed to obtain a molecular‐level understanding of the ring‐opening polymerization mechanism involving TCE as initiator. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 563–569     

原子转移自由基聚合与高分子构筑

活性聚合反应是目前高分子合成研究最为活跃的领域之一，原子转移自由基聚合反应（ATRP）是实现活性聚合的一种有效途径，可实现多种单体的活性聚合和可控自由基聚合。本文介绍了原子转移自由基聚合反应机理，重点综述了原子转移自由基聚合在高分子合成中的应用。     

原子转移自由基细乳液聚合*

本文从正向、反向、同时正向/反向、电子转移活化剂等不同原子转移自由基聚合（ATRP）细乳液引发体系的角度,综述了近年来国内外关于ATRP细乳液聚合的研究进展。在细乳液体系中进行正向ATRP,聚合可控性不理想,反向ATRP相对适合于细乳液体系,其缺点是表面活性剂用量较大。同时正向/反向引发体系的ATRP中催化剂用量大为减少,并且聚合具有良好的可控性;电子转移活化剂（AGET）ATRP是通过电子转移反应来还原过渡金属的氧化态,克服了同时正向/反向ATRP中需要引入自由基引发剂的缺点。     

原子转移自由基聚合及可控自由基聚合

以作者在原子转移自由基聚合领域的研究成果为主导,结合国内外文献,对近年来出现的颇具影响的可控自由基聚合体系与进行了评述与展望。     

Copper‐Mediated Controlled/“Living” Radical Polymerization in Polar Solvents: Insights into Some Relevant Mechanistic Aspects

The field of transition‐metal‐mediated controlled/“living” radical polymerization (CLRP) has become the subject of intense discussion regarding the mechanism of this widely‐used and versatile process. Most mechanistic analyses (atom transfer radical polymerization (ATRP) vs. single‐electron transfer living radical polymerization (SET‐LRP)) have been based on model experiments, which cannot correctly mimic the true reaction conditions. We present, for the first time, a determination of the [Cu^IBr]/[L] (L=nitrogen‐based chelating ligand) ratio and the extent of Cu^IBr/L disproportionation during CLRP of methyl acrylate (MA) in dimethylsulfoxide (DMSO) with Cu⁰ wire as a transition‐metal catalyst source. The results suggest that Cu⁰ acts as a supplemental activator and reducing agent of Cu^IIBr₂/L to Cu^IBr/L. More importantly, the Cu^IBr/L species seem to be responsible for the activation of SET‐LRP.     

Employing Imine Macrocycle Ligand in the Atom Transfer Radical Polymerization of Methyl Methacrylate

Imine macrocycle M₁ was successfully used in conjunction with CuBr as a catalytic system in the atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA). The role of the reaction conditions was clearly observed. Such reaction conditions were found to be the molar ratios of the reactants, the chosen initiating systems, and some additional ambient conditions (e.g. temperature, solvent). MMA homopolymers were successively prepared via ATRP by using benzhydrylbromide, diethylmethylbromomalonate initiating systems under the appropriate reaction conditions. Definite well‐known structures of the formed polymers were unambiguously identified with ¹H NMR.     

AGET ATRP of acrylonitrile using 1,1,4,7,10,10‐hexamethyltriethylenetetramine as both ligand and reducing agent

Atom transfer radical polymerization using activators generated by electron transfer (AGET ATRP) of acrylonitrile (AN) initiated by ethyl 2‐bromoisobutyrate was approached for the first time using 1,1,4,7,10,10‐hexamethyltriethylenetetramine (HMTETA) and 1,1,4,7,7‐pentamethyldiethylenetriamine (PMDETA) as both ligand and reducing agent. AGET ATRP of AN with HMTETA as both ligand and reducing agent was better controlled than with PMDETA as both ligand and reducing agent under the same experimental conditions. With an increase content of HMTETA, the polymerization provided an accelerated reaction rate and a broader polymer molecular weight distribution. The rate of polymerization with DMF as solvent was faster than with acetonitrile, cyclohexanone, toluene, and xylene as solvents. The polymerization apparent activation energy was calculated to be 45.7 kJ mol^?1. The end functionality of polyacrylonitrile (PAN) was confirmed by ¹H NMR spectroscopy. The living feature of PAN was verified by chain extensions of PAN with methyl methacrylate and AN. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 128–133, 2010     

Slightly Cross‐Linked Polyrotaxanes Made by Linking α‐Cyclodextrins Entrapped in Polyrotaxanes Using Hexamethylene Diisocyanate

In this study polyrotaxane (PR)‐based triblock copolymers were first synthesized via the atom transfer radical polymerization (ATRP) of N‐isopropylacrylamide initiated with the self‐assembly of a distal 2‐bromoisobutyryl end‐capped Pluronic 17R4 with a varying amount of α‐cyclodextrins (α‐CDs) in the presence of CuCl/PMDETA at 25°C in aqueous solution. The α‐CDs entrapped on the copolymer chain were then linked with hexamethylene diisocyanate to give rise to novel slightly cross‐linked polyrotaxanes (SCPRs) in DMF at 45°C. The structures of the PR‐based triblock copolymers and SCPRs were characterized by ¹H NMR, ¹³C CP/MAS, GPC and TGA analyses. The number‐average molecular weight of the resulting SCPRs was nearly three and five times of their precursor after linking with a low polydispersity index range of 1.08–1.28. The thermo‐responsive transition of both PR‐based supramolecular polymers in aqueous solution was demonstrated by turbidity measurements and the self‐aggregated morphologies were also evidenced by TEM observations.