Activators Generated By Electron Transfer Research Articles

Surface modification of polymer latex particles by AGET ATRP of a styrene derivative bearing a lactose residue

Grafting of a styrene derivative bearing a lactose residue, i.e., N-2-4-(vinylbenzenesulfonamido)ethyl lactobionamide (VBSAELA), onto polymer latex particles was carried out in aqueous media by activator generated electron transfer atom transfer radical polymerization (AGET ATRP). The core polymer latex particles having α-chloroester groups as ATRP-initiating groups were prepared by miniemulsion polymerization of styrene and 2-chloropropionyloxyethyl methacrylate (CPEM) in the presence of a polymerizable surfactant, i.e., N, N-dimethyl- N-dodecyl- N-2-methacryloyloxyethylammonium bromide (C 12Br). AGET ATRP was initiated with tris[(2-pyridylmethyl)amine] copper (II) dichloride and l-ascorbic acid. Dynamic light scattering (DLS) revealed that the P(St-CPEM)- g-P(VBSAELA) particles possess graft layers of 10 nm in thickness on the core particles of 91 nm in diameter. Critical coagulation concentration measurement revealed that the dispersion stability of the particles in water increased due to hydrated P(VBSAELA) shell layers. Adsorption of bovine serum albumin (BSA) onto the particles was considerably suppressed by the hydrated shell layers.

AGET ATRP of Acrylamide in Aqueous Media

AbstractThe recently developed initiation system, the activator generated by electron transfer (AGET) was used in atom transfer radical polymerization (ATRP) to synthesize well-controlled polyacrylamide in aqueous media at 25°C. The different reducing agents involved ascorbic acid and glucosa; well-controlled polymers were obtained when ascorbic acid was used as water-soluble reducing agent. The polymerizations targeted at degrees of polymerization in the range of 400 resulted in polymers with low polydispersity indices. Moreover, first order plots were linear.

Dispersion Atom Transfer Radical Polymerization of Vinyl Monomers in Supercritical Carbon Dioxide

Controlled dispersion atom transfer radical polymerization (ATRP) of methyl methacrylate (MMA) was successfully carried out in supercritical carbon dioxide in the presence of aminated fluoropolymers. These materials played the dual role of macroligand for the copper bromide and also steric stabilizer to support formation of polymer microspheres. The livingness of the PMMA beads was confirmed by the one-pot two-step PMMA chain extension and the synthesis of poly(methyl methacrylate)-b-poly(2,2,2-trifluoroethyl methacrylate) (PMMA-b-PFMA) diblock copolymer in scCO2. Successful activator generated by electron transfer (AGET) for ATRP of MMA, using tin ethylhexanoate as a reducing agent, is also discussed, and the concept of dispersion ATRP of MMA was successfully extended to the controlled dispersion polymerization of styrene by ATRP leading to the formation of PS microparticles. Finally, due to the high solubility of the catalyst in scCO2, the purification of PMMA was investigated by supercritical fluid ext...

Modification of Cellulose by Using Atom Transfer Radical Polymerization and Ring-Opening Polymerization

The cellulose chloroacetate (Cell-ClAc) with a degree of substitution (DS) value of about 2.1 was synthesized through acylation reaction of microcrystalline cellulose in a homogeneous solution of dimethylacetamide/lithium chloride (DMAc/LiCl), and pyridine as the acid acceptor. Atom transfer radical polymerizations (ATRP) of 3-ethyl-3-methacryloyloxymethyloxetane (EMO) and methyl methacrylate (MMA) were carried out by using Cell-ClAc as the initiator. Furthermore, the second ATRP reactions of MMA and EMO by using the products of Cell-PEMO and Cell-PMMA as initiators were performed, respectively. It was based on the consideration of that the terminal halogens of Cell-PEMO or Cell-PMMA possess activity even after a long time period and could be used as initiator for another ATRP reaction. Different reactions including the activators generated by electron transfer (AGET) ATRP of EMO or MMA and the Ring-Opening Polymerization (ROP) of aliphatic cyclic ester (CE) (ε-caprolactone (CL), or L-Lactide (LLA)) proceed in a same reaction system simultaneously by using the same initiator of Cell-ClAc or Cell-PEMO or Cell-PMMA were also carried out. For analyses of products, the measurements of FT-IR, DSC, TG-DTA, WAXD were performed, and a Polarizing Microscope (POM) was also used for crystal observation of the products. All the measurement results proved the proceeding of the reactions.

High Yield Synthesis of Molecular Brushes via ATRP in Miniemulsion

Molecular brushes were successfully synthesized in miniemulsion systems via activators generated by electron transfer (AGET) ATRP. Confinement of the polymerization reaction within miniemulsion droplets (Dhydro = 275 ± 10 nm) effectively avoided the problem of macroscopic gelation observed in bulk polymerization. The side-chain polymers grew rapidly from the backbones within the droplets which resulted in high monomer conversion in a relatively short time. Molecular visualization by AFM proved that a small amount of cross-linking did occur only at high monomer conversions. However, this microscopic gelation showed no effect on the miniemulsion stability, and therefore the synthesized materials can still be easily used. Thus, the miniemulsion approach leads to preparation of polymer brushes in higher yields as compared to bulk or solution processes.

Methylaluminoxane as a Reducing Agent for Activators Generated by Electron Transfer ATRP

Activators generated by electron transfer (AGET) atom transfer radical polymerization (ATRP) of n‐butyl acrylate (nBA) was carried out in the presence of methylaluminoxane (MAO) as a new reducing agent for Cu(II) complexes. The molecular weights of the produced poly(nBA) increased with nBA conversions with low polydispersities (∼1.2) and they were close to the theoretical values. The polymerization proceeded successfully using five‐fold excess of MAO over Cu(II) complex. UV‐VIS measurements confirmed that MAO reduced the Cu(II) complex. When the mixture of MAO was monitored by UV‐VIS spectroscopy, a decrease of the peak absorbing at 950 nm attributed to CuCl2/tri(2‐pyridylmethyl)amine (TPMA) complex in N, N‐dimethylformamide (DMF) at room temperature was observed as soon as MAO was added.

Development of an ab Initio Emulsion Atom Transfer Radical Polymerization: From Microemulsion to Emulsion

Atom transfer radical polymerization (ATRP) has been successfully extended to an ab initio emulsion system using a "two-step" procedure, in which the final emulsion polymerization system was formed by adding monomer to an ongoing microemulsion ATRP. The newly developed AGET (activators generated by electron transfer) initiation technique was employed in the first stage of this ab initio ATRP. It allows using oxidatively stable Cu(II) species that is reduced in situ by ascorbic acid. The surfactant concentration in the final emulsion system was efficiently decreased to approximately 2 wt % (approximately 10 wt % vs monomer) by decreasing the catalyst concentration and changing the ratio of the monomer added at the microemulsion stage to the monomer added during the second stage. This two-step procedure avoids the necessity of transporting catalysts through the aqueous media during polymerization, resulting in a controlled emulsion polymerization, as evidenced by a linear first-order kinetic plot and formation of a polymer with a relatively narrow molecular weight distribution (Mw/Mn = 1.2-1.4). The polymerization typically reached 70-90% monomer conversion in 5-6 h. The resulting polymer had high chain-end functionality and was successfully chain extended to form in situ block copolymers by adding the second monomer to an ongoing emulsion polymerization. The stable latex from the ab initio emulsion ATRP had a particle size approximately 120 +/- 10 nm.

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

AbstractAtom 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

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

AbstractSummary: 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 $\overline M _{\rm n}$ = 14 000 g · mol−1 and a low polydispersity ($\overline M _{\rm w} /\overline M _{\rm n}$ = 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 $\overline M _{\rm n}$ of 13 400 g · mol−1 and a low polydispersity index ($\overline M _{\rm w} /\overline M _{\rm n}$ = 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).magnified imageAppearance 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).

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.