AGET Atom Transfer Radical Polymerization Research Articles

Experimental Investigation of Methyl Methacrylate in Stirred Batch Emulsion Reactor: AGET ATRP Approach.

This study examines the ab initio emulsion atom transfer radical polymerization (ATRP) initiated by an eco-friendly reducing agent to produce poly(methyl methacrylate) (PMMA) polymer with controlled characteristics in a 2 L stirred batch reactor. The effect of the reaction temperature, surfactant concentration, monomer to water ratio, and stirring speed was thoroughly investigated. The results showed that PMMA coagulation becomes quite severe at a certain temperature threshold. However, the coagulation could be avoided at mild reaction temperature, since the outcomes showed that loading more surfactant to the system under high mixing speed has balanced the polymer mixture and yielded high monomer conversion. The PMMA product was analyzed by gravimetry and GPC measurements and after 5 h of polymerization at a reaction temperature of 50 °C, monomer conversion of 64.1% was obtained, and PMMA polymer samples produced had an average molar mass of 4.5 kg/mol and a polydispersity index of 1.17. The structure of the PMMA polymer was successfully proved by FTIR and nuclear magnetic resonance (NMR) spectroscopy. The results confirm the living feature of MMA AGET ATRP in emulsion medium and recommend further investigation for other types of surfactant.

Development of Environmentally Friendly Atom Transfer Radical Polymerization.

Atom transfer radical polymerization (ATRP) is one of the most successful techniques for the preparation of well-defined polymers with controllable molecular weights, narrow molecular weight distributions, specific macromolecular architectures, and precisely designed functionalities. ATRP usually involves transition-metal complex as catalyst. As the most commonly used copper complex catalyst is usually biologically toxic and environmentally unsafe, considerable interest has been focused on iron complex, enzyme, and metal-free catalysts owing to their low toxicity, inexpensive cost, commercial availability and environmental friendliness. This review aims to provide a comprehensive understanding of iron catalyst used in normal, reverse, AGET, ICAR, GAMA, and SARA ATRP, enzyme as well as metal-free catalyst mediated ATRP in the point of view of catalytic activity, initiation efficiency, and polymerization controllability. The principle of ATRP and the development of iron ligand are briefly discussed. The recent development of enzyme-mediated ATRP, the latest research progress on metal-free ATRP, and the application of metal-free ATRP in interdisciplinary areas are highlighted in sections. The prospects and challenges of these three ATRP techniques are also described in the review.

A Facial Strategy for Catalyst and Reducing Agent Synchronous Separation for AGET ATRP Using Thiol-Grafted Cellulose Paper as Reducing Agent.

Atom Transfer Radical Polymerization (ATRP) has been a powerful tool to synthesize well-defined functional polymers, which are widely used in biology, drug/gene delivery and antibacterial materials, etc. However, the potential toxic residues in polymer reduced its service life and limited its applications. In order to overcome the problem, in this work, a novel polymerization system of activators generated by electron transfer for atom transfer radical polymerization (AGET ATRP) for synchronous separation of the metal catalyst and byproduct of reducing agent was developed, using thiol-grafted cellulose paper (Cell-SH) as a solid reducing agent. The polymerization kinetics were investigated in detail, and the “living” features of the novel polymerization system were confirmed by chain-end analysis and chain extension experiment for the resultant polymethyl methacrylate (PMMA). It is noted that the copper residual in obtained PMMA was less than 20 ppm, just by filtering the sheet-like byproduct of the reducing agent.

AGET ATRP of Poly[poly(ethylene glycol) methyl ether methacrylate] Catalyzed by Hydrophobic Iron(III)–Porphyrins

Commercially available hydrophobic porphyrins are investigated as an environmentally friendly catalytic system for iron‐mediated atom transfer radical polymerization (ATRP) of poly(ethylene glycol) monomethyl ether methacrylate (PEGMA). Polymerizations in organic solvent are optimized using activators generated by electron transfer (AGET ATRP), based on iron(III)–porphyrin complexes, and tin(II) 2‐ethyl hexanoate or ascorbic acid as a reducing agent. Copper‐free PPEGMA macromolecules are obtained with high conversion, controlled molecular weight, and polydispersity index compared with standard copper‐based ATRP. The facile preparation and availability of the catalyst, together with its expected low toxicity, represent clear advantages for the synthesis of PPEGMA‐based materials for biomedical use. image

AGET ATRP of Methyl Methacrylate Based on Thermoregulated Phase Transfer Catalysis in Organic/Aqueous Biphasic System: Facile and Highly Efficient In Situ Catalyst/Ligand Separation and Recycling

A novel polymerization system with activators generated by electron transfer for atom transfer radical polymerization (ATRP) for sustainable catalyst/ligand separation and recycling in situ is developed based on thermoregulated phase transfer catalysis in organic/aqueous biphasic system. Herein, a typical iniferter agent 1-cyano-1-methylethyldiethyldithiocarbamte is used as the initiator, and CuBr2, monomethoxy poly(ethylene glycol)-350-supported substituted dipicolylamine (L350), ascorbic acid, and methyl methacrylate are employed as the catalyst, thermoresponsive ligand, reducing agent, and the model monomer, respectively. The “living” nature of the system is confirmed by polymerization kinetics with recycled catalyst complex aqueous solution and chain-extension experiments via iniferter and ATRP mechanism, respectively. In addition, the catalyst residue in polymers is less than 2 ppm and the recycling efficiency of catalyst complex in water kept more than 95% even after 5 times of recovery experiments while keeping narrow molecular weight distribution (Mw/Mn < 1.33).

Robust grafting of PEG-methacrylate brushes from polymeric coatings

A study is presented of the grafting of poly(ethylene glycol)methyl ether methacrylate (PEGMA) from polymeric macroinitiator films to form well-defined polymer brushes, using activators generated/regenerated by electron transfer (AGET/ARGET) atom transfer radical polymerization (ATRP). Polymer brush coatings can potentially be obtained on surfaces of virtually any shape and composition, because of the ease of conformal casting of the anchoring macroinitiator film. Polymer brush coatings are synthesized in a robust way, as ARGET and AGET ATRP require little to no deoxygenation and make use of stable catalysts. The monomer, catalyst, ligand and reducing agent concentrations, the amount and type of initiating moiety in the anchoring films, and the choice of solvents are optimized, resulting in control over the rate of reaction, and the molecular weight of poly(PEGMA). The best conditions are determined for the formation of a poly(PEGMA) brush with high grafting density, controlled thickness and “living” ends available for post-functionalization.

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.

Target-Triggered Polymerization for Biosensing

Because of the potential applications of biosensors in clinical diagnosis, biomedical research, environmental analysis, and food quality control, researchers are very interested in developing sensitive, selective, rapid, reliable, and low-cost versions of these devices. A classic biosensor directly transduces ligand-target binding events into a measurable physical readout. Because of the limited detection sensitivity and selectivity in earlier biosensors, researchers have developed a number of sensing/signal amplification strategies. Through the use of nanostructured or long chain polymeric materials to increase the upload of signal tags for amplification of the signal readout associated with the ligand-target binding events, researchers have achieved high sensitivity and exceptional selectivity. Very recently, target-triggered polymerization-assisted signal amplification strategies have been exploited as a new biosensing mechanism with many attractive features. This strategy couples a small initiator molecule to the DNA/protein detection probe prior to DNA hybridization or DNA/protein and protein/protein binding events. After ligand-target binding, the in-situ polymerization reaction is triggered. As a result, tens to hundreds of small monomer signal reporter molecules assemble into long chain polymers at the location where the initiator molecule was attached. The resulting polymer materials changed the optical and electrochemical properties at this location, which make the signal easily distinguishable from the background. The assay time ranged from minutes to hours and was determined by the degree of amplification needed. In this Account, we summarize a series of electrochemical and optical biosensors that employ target-triggered polymerization. We focus on the use of atom transfer radical polymerization (ATRP), as well as activator generated electron transfer for atom transfer radical polymerization (AGET ATRP) for in-situ formation of polymer materials for optically or electrochemically transducing DNA hybridization and protein-target binding. ATRP and AGET ATRP can tolerate a wide range of functional monomers. They also allow for the preparation of well-controlled polymers with narrow molecular weight distribution, which was predetermined by the concentration ratio of the consumed monomer to the introduced initiator. Because the reaction initiator can be attached to a variety of detection probes through well-established cross-linking reactions, this technique could be expanded as a universal strategy for the sensitive detection of DNA and proteins. We see enormous potential for this new sensing technology in the development of portable DNA/protein sensors for point-of-need applications.

Iron(III)‐Mediated AGET ATRP of Methyl Methacrylate Using Vitamin C Sodium Salt as a Reducing Agent

AbstractVitamin C sodium salt (VC‐Na) is used as a reducing agent for the iron‐mediated AGET ATRP (atom transfer radical polymerization using activators generated by electron transfer) of methyl methacrylate (MMA) with FeCl3/tris‐(3,6‐dioxa‐heptyl) amine (TDA‐1) as a catalyst complex and ethyl 2‐bromoisobutyrate (EBiB) as an initiator in the absence/presence of a limited amount of air. As compared with the reported iron‐mediated AGET ATRP of MMA, the current catalyst system shows a faster polymerization rate. For example, a conversion of 82.3% is obtained in 3.1 h with a molar ratio of [MMA]0/[EBiB]0/[FeCl3.6H2O]0/[TDA‐1]0/[VC‐Na]0 = 500:1:1:3:0.5 at 90 °C. The kinetics of polymerizations of MMA in bulk or anisole demonstrate features of “living” or controlled free‐radical polymerization, such as the number‐average molecular weights increasing linearly with monomer conversion and maintaining narrow molecular weight distributions ($\overline {M} _{w} $/$\overline {M} _{n} $ = 1.20–1.44). magnified image

Synthesis, characterization, and rheological properties of multiarm stars with poly(glycidol) core and poly(methyl methacrylate) arms by AGET ATRP

Well-defined multiarm star block copolymers poly(glycidol)-b-poly(methyl methacrylate) (PGOHBr-b-PMMAx) with an average number of PMMA arms of 85, 55, and 45 have been prepared. The core-first approach has been selected as the methodology using atom transfer radical polymerization (ATRP) of MMA from an activated hyperbranched poly(glycidol) as the core. These activated hyperbranched macroinitiators were prepared by esterification of hyperbranched poly(glycidol) (PGOH) with 2-bromoisobutyryl bromide. The effect of monomer/initiator ratio, catalyst concentration, time, temperature, and solvent on the growing of the arms has been studied in detail in order to optimize the process and to diminish the radical-radical coupling. The final products and intermediates were characterized by means of size exclusion chromatography (SEC), nuclear magnetic resonance (NMR) and Fourier transform-infrared (FTIR) spectroscopy. The length of PMMA arms was determined by SEC after cleavage of ester bond linked to PGOH core. Glass transition temperature (Tg), thermal stability and rheological properties of the multiarm star copolymers were also studied. Finally, tapping mode atomic force microscopy (TMAFM) allowed the clear visualization of nano-sized particles (80–200 nm) corresponding to individual star molecules. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Biotin‐, Pyrene‐, and GRGDS‐Functionalized Polymers and Nanogels via ATRP and End Group Modification

AbstractFunctionality, one of the key attributes of atom transfer radical polymerization (ATRP), was utilized for the synthesis of well‐controlled polymers functionalized with biotin, pyrene, and peptides. Hydroxy‐functionalized poly(oligo(ethylene oxide) monomethyl ether methacrylate) (HO‐POEOMA) was prepared by AGET ATRP of OEOMA initiated by 2‐hydroxyethyl 2‐bromoisobutyrate in water or in inverse miniemulsion of water/cyclohexane at ambient temperature. HO‐POEOMA was then further functionalized with biotin, pyrene, and GRGDS peptide. In addition, ATRP and click chemistry offered an efficient route for the synthesis of telechelic di‐biotin polymers. These general methods can be applied to the formation of different functional materials conjugated with proteins, dyes, nucleic acids, and drugs.magnified image

Mixed Molecular Brushes with PLLA and PS Side Chains Prepared by AGET ATRP and Ring-Opening Polymerization

Brush macromolecules having poly(l-lactide) (PLLA) and poly(styrene) (PS) side chains were prepared on the backbone of partially esterified poly(2-hydroxyethyl methacrylate) (PHEMA) by using a combination of atom transfer radical polymerization (ATRP) and ring-opening polymerization. The number-average degrees of polymerization of PLLA side chains and PS side chains were determined by 1H NMR spectroscopy, and the apparent molecular weights of the brush molecules were measured by gel permeation chromatography. The relationship between the crystallization of PLLA with PLLA and PS side chain lengths was investigated. Inside a brush molecule due to the unfavorable interaction between PLLA and PS two phases were formed. Brush molecules adsorbed on mica tend to make a starlike conformation; however, they change to a globular conformation after thermal treatment.

Activator Generated by Electron Transfer for Atom Transfer Radical Polymerization

A novel procedure was developed for activation of an oxidatively stable catalyst complex added to an atom transfer radical polymerization (ATRP). Tin(II) 2-ethylhexanoate (Sn(EH)2) was used as a reducing agent of various Cu(II) complexes in ATRP of various monomers initiated by alkyl halides. This approach further improves a simultaneous normal and reverse initiation (SR&NI) by eliminating free radical initiators for the activation of the higher oxidation state catalyst complex. As a result, “activator generated by electron transfer” (AGET) ATRP allows the preparation of pure block copolymers. Several combinations of monomer/catalyst complex precursor were studied, including styrene/CuCl2/dNbpy, octadecyl methacrylate/CuCl2/dNbipy, methyl methacrylate/CuCl2/PMDETA, n-butyl acrylate/CuBr2/PMDETA, and methyl acrylate/CuCl2/Me6TREN. Polymerization proceeded in a controlled way for all systems, producing well-defined polymers with controlled degree of polymerization and narrow molecular weight distribution, demonstrating the robust nature of AGET ATRP. Additionally, Sn(EH)2 was used simultaneously as a reducing agent for ATRP of octadecyl methacrylate and a catalyst for ring-opening polymerization (ROP) of ε-caprolactone, allowing direct synthesis of the corresponding block copolymer.