Atom Transfer Radical Polymerization System Research Articles

Exploring solution ICAR ATRP of methyl acrylate with AIBN as azo initiator: a kinetic modeling and simulation study

Supplementary techniques to atom transfer radical polymerization (ATRP) have been studied to reduce the concentration of catalytic complexes used, aiming at a less costly and more environmentally friendly process for synthesizing polymeric materials. Initiators for continuous activator regeneration ATRP (ICAR ATRP) is one technique in which a source of primary free radicals allows the reactivation of catalytic species used in the conventional ATRP. Due to the technological relevance of the topic, this work aims to expand the contribution to literature with kinetic modeling and simulation study for an ICAR ATRP system not yet explored. For this purpose, it was investigated solution ICAR ATRP of methyl acrylate with copper-based catalysts and azobisisobutyronitrile as ICAR initiator. The method of moments was employed to derive material balance equations. We find that the kinetic mechanism that best represented the trends of experimental data from literature was the one that considered specific side reactions of acrylates, such as backbiting and radical catalytic termination. In the model fitting procedure, a nonlinear optimization process had to be developed to estimate the values of kinetic rate constants not yet reported in the literature. The values obtained for the missing kinetic rate constants are consistent with similar experimental systems found in the literature. The deterministic model obtained was then employed to study the concentration profile maps. Simulations allowed verifying the slow release of primary free radicals from ICAR initiator to reduce the deactivators in activators species continuously. In addition, it was possible to confirm that the ICAR ATRP can be thermoregulated. Parametric analyses showed that variations in kinetic rate constants and reaction stoichiometry can shape monomer conversion and the molecular properties of the polymer (e.g., molecular weight, dispersity, and end functionality).

Atom Transfer Radical Polymerization: A Mechanistic Perspective.

Since its inception, atom transfer radical polymerization (ATRP) has seen continuous evolution in terms of the design of the catalyst and reaction conditions; today, it is one of the most useful techniques to prepare well-defined polymers as well as one of the most notable examples of catalysis in polymer chemistry. This Perspective highlights fundamental advances in the design of ATRP reactions and catalysts, focusing on the crucial role that mechanistic studies play in understanding, rationalizing, and predicting polymerization outcomes. A critical summary of traditional ATRP systems is provided first; we then focus on the most recent developments to improve catalyst selectivity, control polymerizations via external stimuli, and employ new photochemical or dual catalytic systems with an outlook to future research directions and open challenges.

Mechanically induced atom transfer radical polymerization with high efficiency via piezoelectric heterostructures

A facile ultrasonication induced atom transfer radical polymerization (ATRP) mediated via piezoelectric heterostructure was developed. ZnO/BaTiO 3 heterostructure was prepared by in-situ deposition of zinc precursor on BaTiO 3 particles followed by high temperature annealing. Under ultrasonic activation, as-synthesized piezoelectric ZnO/BaTiO 3 heterostructure with an elevated macroscopic polarization could facilitate piezoelectric induced electron-hole pairs with more efficient separation and transfer, leading to the enhanced piezocatalytic in controlled living polymerization. High efficiency of ultrasonication mediated ATRP of methyl methacrylate (MMA) by ZnO/BaTiO 3 heterostructure about 63.1% conversion was achieved under 4 h ultrasonic agitation, providing PMMA homopolymer with well-defined molecular weight, narrow molecular dispersity and high end-group fidelity. Furthermore, implications of CuBr 2 /TPMA concentrations, piezoelectric materials, ZnO/BaTiO 3 heterostructure loading and distinct monomer were systematically investigated. Process of ultrasonication-mediated ATRP could be readily controlled by ultrasound switch on/off. The versatility of ultrasonication-mediated ATRP system was further verified by the preparation of star-like polymer. The ability of transfer piezoelectric-induced electrons from ZnO/BaTiO 3 heterostructure to CuBr 2 /TPMA and nature of ZnO/BaTiO 3 heterostructure were investigated to reveal the mechanism of ultrasonication mediated ATRP. A facile and robust atom transfer radical polymerization catalyzed by piezocatalyst with high efficiency was developed in this study. • Piezoelectric catalyst enabled mechanically induced atom transfer radical polymerization with high efficiency.

Dimensional Optimization for ZnO-Based Mechano-ATRP with Extraordinary Activity.

Various piezoelectric nanomaterials were utilized in ultrasound-mediated atom transfer radical polymerization (ATRP), owing to their outstanding piezoelectric effect. However, the relationship between the morphology of those piezocatalysts and polymerization has not been clearly established. Herein, we employed different piezoelectric zinc oxide (ZnO) nanomaterials to achieve novel mechano-induced ATRP (mechano-ATRP). Based on the synergistic effect of piezoelectric properties and specific surface area, the catalytic activity of 1D ZnO nanorods (1D-ZnO NRs) with increased aspect ratio outperformed that of 0D ZnO nanoparticles (0D-ZnO NPs). Compared to the conventional ATRP system, this system exhibited extraordinary activity toward the less activated monomer acrylonitrile (67% conversion after 6 h), with a narrow molecular weight distribution (polydispersity index ∼ 1.19). Furthermore, implications of ZnO loading, copper salt amount, degree of polymerization, monomer, and solvent were also studied for the highly efficient mechano-ATRP.

Making ATRP More Practical: Oxygen Tolerance.

Atom-transfer radical polymerization (ATRP) is a well-known technique for the controlled polymerization of vinyl monomers under mild conditions. However, as with any other radical polymerization, ATRP typically requires rigorous oxygen exclusion, making it time-consuming and challenging to use by nonexperts. In this Account, we discuss various approaches to achieving oxygen tolerance in ATRP, presenting the overall progress in the field.Copper-mediated ATRP, which we first discovered in the late 1990s, uses a CuI/L activator that reversibly reacts with the dormant C(sp3)-X polymer chain end, forming a X-CuII/L deactivator and a propagating radical. Oxygen interferes with activation and chain propagation by quenching the radicals and oxidizing the activator. At ATRP equilibrium, the activator is present at a much higher concentration than the propagating radicals. Thus, oxidation of the activator is the dominant inhibition pathway. In conventional ATRP, this reaction is irreversible, so oxygen must be strictly excluded to achieve good results.Over the last two decades, our group has developed several ATRP techniques based on the concept of regenerating the activator. When the oxidized activator is continuously converted back to its active reduced form, then the catalytic system itself can act as an oxygen scavenger. Regeneration can be accomplished by reducing agents and photo-, electro-, and mechanochemical stimuli. This family of methods offers a degree of oxygen tolerance, but most of them can tolerate only a limited amount of oxygen and do not allow polymerization in an open vessel.More recently, we discovered that enzymes can be used in auxiliary catalytic systems that directly deoxygenate the reaction medium and protect the polymerization process. We developed a method that uses glucose oxidase (GOx), glucose, and sodium pyruvate to very effectively scavenge oxygen and enable open-vessel ATRP. By adding a second enzyme, horseradish peroxidase (HPR), we managed to extend the role of the auxiliary enzymatic system to generating carbon-based radicals and changed ATRP from an oxygen-sensitive to an oxygen-fueled reaction.While performing control experiments for the enzymatic methods, we noticed that using sodium pyruvate under UV irradiation triggers polymerization without the presence of GOx. This serendipitous discovery allowed us to develop the first oxygen-proof, small-molecule-based, photoinduced ATRP system. It has oxygen tolerance similar to that of the enzymatic methods, exhibits superior compatibility with both aqueous media and organic solvents, and avoids problems associated with purifying polymers from enzymes. The system was able to rapidly polymerize N-isopropylacrylamide, a challenging monomer, with a high degree of control.These contributions have substantially simplified the use of ATRP, making it more practical and accessible to everyone.

Concurrent atom transfer radical polymerization and nitroxide radical coupling relay polymerization.

Simultaneous atom transfer radical polymerization (ATRP) and nitroxide radical coupling (NRC) seems impossible because the presence of nitroxide radicals would quench the radical polymerization immediately. However, by combining a nitroxide radical and an ATRP active halogen, a halogen group that can initiate one polymer chain by ATRP, into one functional reagent and adding this functional reagent to an ATRP system, concurrent ATRP-NRC relay polymerization was carried out successfully under proper reaction conditions. The key to success was the conjugate radical trapping and re-initiation took place repeatedly, resulting in polymers with inserted alkoxyamine linkages. This novel relay polymerization method provides numerous possibilities for macromolecular architecture/functionality tailoring by using of different functional reagents.

End Group Stability of Atom Transfer Radical Polymerization (ATRP)-Synthesized Poly(N-isopropylacrylamide): Perspectives for Diblock Copolymer Synthesis.

Studies on the end group stability of poly(N-isopropylacrylamide) during the atom transfer radical polymerization (ATRP) process are presented. Polymerization of N-isopropylacrylamide was conducted in different solvents using a copper(I) chloride/Me6Tren catalyst complex. The influence of the ATRP solvent as well as the polymer purification process on the end group stability was investigated. For the first time, mass spectrometry results clearly underline the loss of ω end groups via an intramolecular cyclization reaction. Furthermore, an ATRP system based on a copper(I) bromide/Me6Tren catalyst complex was introduced, that showed not only good control over the polymerization process, but also provided the opportunity of block copolymerization of N-isopropylacrylamide with acrylates and other N-substituted acrylamides. The polymers were characterized using 1H-NMR spectroscopy and size exclusion chromatography. Polymer end groups were determined via ESI-TOF mass spectrometry enhanced by ion mobility separation (IMS).

Experimental and computational investigation of oxidative quenching governed aqueous organocatalyzed atom transfer radical polymerization

A water-soluble organic photoredox catalyst, 3,7-methoxypolyethylene glycol 1-naphthalene-10-phenoxazine (Naph-PXZ-PEG), that can catalyze aqueous organocatalyzed atom transfer radical polymerization (ATRP) via oxidative quenching cycle has been reported for the first time. Comparative studies of Naph-PXZ-PEG and EosinY involved aqueous organocatalyzed ATRP systems have been done via polymerization experiment and kinetic modeling approach. Results showed that the polymerization via oxidative quenching cycle in Naph-PXZ-PEG system proceeded much faster and higher initiator efficiency than the polymerization via reductive quenching cycle in Eosin Y system under same conditions. Detailed information of the Naph-PXZ-PEG was presented by experiments and density functional theory (DFT) simulation. A series of kinetics experiments under different catalyst loadings, initiator concentrations, “on-off” switch of light and chain extension have been conducted and confirmed the good controllability of the current system and high end-group fidelity. This work provides a systematic study on developing an effective water soluble organic catalyst for the preparation of the well-defined polymers by a “green” and sustainable ATRP.

A comparative study on grafting polymers from cellulose nanocrystals via surface-initiated atom transfer radical polymerization (ATRP) and activator re-generated by electron transfer ATRP

Both Surface-Initiated Atom Transfer Radical Polymerization (SI-ATRP) and Surface-Initiated Activator Re-Generated by Electron Transfer ATRP (SI-ARGET ATRP) were performed to graft polystyrene and poly(4-vinylpyridine) on the surface of cellulose nanocrystals (CNCs) to evaluate the potential benefits of each method. The polymer grafted CNCs and their corresponding free polymers initiated from sacrificial initiators were characterized by Fourier transform infrared spectroscopy, gel permeation chromatography, dynamic light scattering, differential scanning calorimetry, thermogravimetric analysis, and elemental analysis, respectively. It was found that SI-ARGET ATRP favored the grafting of longer polymer chains with lower grafting density compared with the classical SI-ATRP. The surface initiation efficiency of brominated CNCs in SI-ARGET ATRP is much lower than that in SI-ATRP, which is mainly due to the much lower amount (ppm level) of catalysts and faster propagation rate in SI-ARGET ATRP system.

Growth of polymer brushes by “grafting from” via ATRP – Monte Carlo simulations

The growth of polymer brushes from flat surfaces via a grafting-from approach by atom transfer radical polymerization (ATRP) was simulated using a Monte Carlo method, the dynamic lattice liquid (DLL) model, under athermal conditions. Sets of probabilities representing reactions participating in ATRP or overall ATRP reaction probability were implemented in the simulation model. The later corresponds to the ATRP system in which statistically less than one monomer is attached to the chain end during its active period. Dense and moderately dense brushes with degrees of polymerization 45–150 were studied assuming various polymerization rates. It was determined that chain length distribution strongly depends on the reaction probability and grafting density (GD). For dense brushes (GD = 0.3–0.6) the dispersity was comparable with the experimental results only for the lowest probabilities used (p = 2 × 10−5). For GD = 0.1 and in the presence of free chains 10 or even 100 times higher probabilities gave satisfactory results. If polymerization rate was too high, two groups of chains could be distinguished: slowly growing short chains, the ends of which were close to the flat surface, where monomer concentration was lower and quickly growing long chains with the ends far from the surface, where monomer concentrations were higher. The relationship between experimental parameters of ATRP and parameters used in the simulations are discussed.

ATRP in Water: Kinetic Analysis of Active and Super-Active Catalysts for Enhanced Polymerization Control

Atom transfer radical polymerization (ATRP) in water is characterized by very high catalytic activity, i.e. the rate constant (kact) of the “activation” reaction between CuI complexes and alkyl halides (RX) is very large. To accurately study such fast reactions in water, we developed a collection of electrochemical methods applicable for the determination of a vast range of kact values (>7 orders of magnitude). These included rate constants of extremely fast reactions with kact > 107 mol–1 dm3 s–1. We studied three widely used ATRP catalysts ([CuIPMDETA]+, [CuITPMA]+, and [CuIMe6TREN]+) and an extended series of water-soluble initiators. Accurate results were obtained in the range 1 < kact < 108 mol–1 dm3 s–1, allowing to build for the first time precise structure–reactivity correlations for aqueous ATRP, in both pure water and water/monomer mixtures. The results were compared to traditional ATRP systems in organic solvents. The collected data greatly expand the available range of investigated catalyst/in...

Well-defined functional mesoporous silica/polymer hybrids prepared by an ICAR ATRP technique integrated with bio-inspired polydopamine chemistry for lithium isotope separation.

Mesoporous silica/polymer hybrids with well-preserved mesoporosity were prepared by integrating the initiators for continuous activator regeneration (ICAR) atom transfer radical polymerization (ATRP) technique with the bio-inspired polydopamine (PDA) chemistry. By manipulating the auto-oxidative polymerization of dopamine, uniform PDA layers were deposited on the surfaces and pore walls of ordered mesoporous silicas (OMSs), thereby promoting the immobilization of ATRP initiators. Poly(glycidyl methacrylate) (PGMA) brushes were then grown from the OMSs by using the ICAR ATRP technique. The evolution of the mesoporous silica/polymer hybrids during synthesis, in terms of morphology, structure, surface and porous properties, was detailed. And, parameters influencing the controlled growth of polymer chains in the ICAR ATRP system were studied. Taking advantage of the abundant epoxy groups in the PGMA platform, post-functionalization of the mesoporous silica/polymer hybrids by the covalent attachment of macrocyclic ligands for the adsorptive separation of lithium isotopes was realized. Adsorption behavior of the functionalized hybrids toward lithium ions was fully investigated, highlighting the good selectivity, and effects of temperature, solvent and counter ions. The ability for lithium isotope separation was evaluated. A higher separation factor could be obtained in systems with softer counter anions and lower polarity solvents. More importantly, due to the versatility of the ICAR ATRP technique, combined with the non-surface specific PDA chemistry, the methodology established in this work would provide new opportunities for the preparation of advanced organic-inorganic porous hybrids for broadened applications.

Electrochemical Atom Transfer Radical Polymerization in Miniemulsion with a Dual Catalytic System.

An electrochemical approach was used to control atom transfer radical polymerization (ATRP) of n-butyl acrylate (BA) in miniemulsion. Electropolymerization required a dual catalytic system, composed of an aqueous phase catalyst and an organic phase catalyst. This allowed shuttling the electrochemical stimulus from the working electrode (WE) to the continuous aqueous phase and to the dispersed monomer droplets. As aqueous phase catalysts, the hydrophilic Cu complexes with the ligands N,N-bis( 2-pyridylmethyl)-2-hydroxyethylamine (BPMEA), 2,2'-bipyridine (bpy), and tris(2-pyridylmethyl)amine (TPMA) were tested. As organic phase catalysts, the hydrophobic complexes with the ligands bis(2-pyridylmethyl)-octadecylamine (BPMODA) and bis[2-(4-methoxy-3,5-dimethyl)-pyridylmethyl]octadecylamine (BPMODA*) were evaluated. Highest rates and best control of BA electropolymerization were obtained with the water-soluble Cu/BPMEA used in combination with the oil-soluble Cu/BPMODA*. The polymerization rate could be further enhanced by changing the potential applied at the WE. Differently from traditional ATRP systems, reactivity of the dual catalytic system did not depend on the redox potential of the catalysts but instead depended on the hydrophobicity and partition coefficient of the aqueous phase catalyst.

Metal-Free Atom Transfer Radical Polymerization of Methyl Methacrylate with ppm Level of Organic Photocatalyst.

It is well known that the recently developed photoinduced metal-free atom transfer radical polymerization (ATRP) has been considered as a promising methodology to completely eliminate transition metal residue in polymers. However, a serious problem needs to be improved, namely, large amount of organic photocatalysts should be used to keep the controllability over molecular weights and molecular weight distributions. In this work, a novel photocatalyst 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) with strong excited state reduction potential is successfully used to mediate a metal-free ATRP of methyl methacrylate just with parts per million (ppm) level usage under irradiation of blue light emitting diode at room temperature, using ethyl α-bromophenyl-acetate as a typical initiator with high initiator efficiency. The polymerization kinetic study, multiple controlled "on-off" light switching cycle regulation, and chain extension experiment confirm the "living"/controlled features of this promising photoinduced metal-free ATRP system with good molecular weight control in the presence of ppm level photocatalyst 4CzIPN.

A Straightforward Estimation of Activation and Deactivation Parameters for ATRP Systems from Actual Polymerization Rate and Molecular Weight Distribution Data

The accuracy of a model prediction relies heavily on the quality of the parameters used. Some of the available methods to estimate the activation and deactivation rate constants in atom transfer radical polymerization (ATRP) are done in the absence of monomer, hence they may not be representative of the polymerization conditions. Others offer great accuracy but requires data that are not commonly measured in experiments. In this study, a simple method is proposed to estimate activation and deactivation rate constants through correlating the recently reported theoretical equations with experimental data of monomer conversion and polymer molecular weight dispersity. The kinetics and dispersity equations used are straightforward and explicit, thus can be easily calculated. Only two parameters (activation and deactivation rate constant) are involved in the correlation of two data sets without any other adjustable parameters. In addition, the experimental data required are some of the most often measured quantities in polymerization, thus no additional experiments or measurements are required. Since the conversion and dispersity are obtained from actual polymerization, the reaction rate constants estimated are representative of the real reaction conditions. The applicability of this method is demonstrated by estimating parameters using reported experimental data of ATRP of methyl methacrylate conducted at various conditions. image

Relation between Overall Rate of ATRP and Rates of Activation of Dormant Species

The rate of atom transfer radical polymerization (ATRP) depends on the rate constant of propagation (kp) and concentration of growing radicals. The latter is related to the ATRP equilibrium constant (KATRP) and concentrations of alkyl halides, activators, and deactivators. Activation of alkyl halides by CuI/L and deactivation of radicals by X–CuII/L are vital processes providing good control in ATRP. Rates of these reactions are typically identical throughout polymerization, since the ATRP equilibrium is maintained in essentially all ATRP systems. There are new ATRP processes carried out with ppm of Cu catalysts, such as activators regenerated by electron transfer (ARGET), initiators for continuous activator regeneration (ICAR), supplemental activators and reducing agents (SARA), and electrochemically or photochemically mediated ATRP (eATRP, photoATRP). In these processes, as in conventional radical polymerization (or in RAFT), concentration of radicals is established by balancing rates of radical generat...

Iron-Mediated Homogeneous ICAR ATRP of Methyl Methacrylate under ppm Level Organometallic Catalyst Iron(III) Acetylacetonate.

Atom Transfer Radical Polymerization (ATRP) is an important polymerization process in polymer synthesis. However, a typical ATRP system has some drawbacks. For example, it needs a large amount of transition metal catalyst, and it is difficult or expensive to remove the metal catalyst residue in products. In order to reduce the amount of catalyst and considering good biocompatibility and low toxicity of the iron catalyst, in this work, we developed a homogeneous polymerization system of initiators for continuous activator regeneration ATRP (ICAR ATRP) with just a ppm level of iron catalyst. Herein, we used oil-soluble iron (III) acetylacetonate (Fe(acac)3) as the organometallic catalyst, 1,1′-azobis (cyclohexanecarbonitrile) (ACHN) with longer half-life period as the thermal initiator, ethyl 2-bromophenylacetate (EBPA) as the initiator, triphenylphosphine (PPh3) as the ligand, toluene as the solvent and methyl methacrylate (MMA) as the model monomer. The factors related with the polymerization system, such as concentration of Fe(acac)3 and ACHN and polymerization kinetics, were investigated in detail at 90 °C. It was found that a polymer with an acceptable molecular weight distribution (Mw/Mn = 1.43 at 45.9% of monomer conversion) could be obtained even with 1 ppm of Fe(acac)3, making it needless to remove the residual metal in the resultant polymers, which makes such an ICAR ATRP process much more industrially attractive. The “living” features of this polymerization system were further confirmed by chain-extension experiment.

A Facile Strategy for Catalyst Separation and Recycling Suitable for ATRP of Hydrophilic Monomers Using a Macroligand.

How to simply and efficiently separate and recycle catalyst has still been a constraint for the wide application of atom transfer radical polymerization (ATRP), especially for the polymerization systems with hydrophilic monomers because the polar functional groups may coordinate with transition metal salts, resulting in abundant catalyst residual in the resultant water-soluble polymers. In order to overcome this problem, a latent-biphasic system is developed, which can be successfully used for ATRP catalyst separation and recycling in situ for various kinds of hydrophilic monomers for the first time, such as poly(ethylene glycol) monomethyl ether methacrylate (PEGMA), 2-hydroxyethyl methacrylate (HEMA), 2-(dimethylamino)ethyl methacrylate (DMAEMA), N,N-dimethyl acrylamide (DMA), and N-isopropylacrylamide (NIPAM). Herein, random copolymer of octadecyl acrylate (OA), MA-Ln (2-(bis(pyridin-2-ylmethyl)amino)ethyl acrylate), and POA-ran-P(MA-Ln) is designed as the macroligand, and heptane/ethanol is selected as the biphasic solvent. Copper(II) bromide (CuBr2 ) is employed as the catalyst, PEG-bound 2-bromo-2-methylpropanoate (PEG350 -Br) as the water-soluble ATRP initiator and 2,2'-azobis(isobutyronitrile) (AIBN) as the azo-initiator to establish an ICAR (initiators for continuous activator regeneration) ATRP system. Importantly, well-defined water-soluble polymers are obtained even though the recyclable catalyst is used for sixth times.

A Molecular Weight Distribution Polydispersity Equation for the ATRP System: Quantifying the Effect of Radical Termination

Polydispersity quantifies the breadth of polymer molecular weight distribution, making it an important and frequently quoted chain microstructural property for characterization. An explicit expression of such an important variable is desirable for ease of calculation, correlation with experiment data, and/or parameter estimation. A review of published literatures shows that great efforts have been put forth by many researchers to derive these equations for various polymerization mechanisms. In atom transfer radical polymerization (ATRP), polydispersity depends on three factors: monomer conversion, number of monomer addition per activation/deactivation cycle, and amount of dead chains. The existing expressions available in the literature only account for, at most, two of these three factors, with the contribution from dead chains commonly neglected. This assumption results in polydispersity monotonically decreasing with conversion, which is often not observed in experiments. In this work, a new equation for polydispersity, which accounts for contributions of all the three aforementioned factors, is proposed. The validity of assumptions involved in the derivation is evaluated by comparing the polydispersity profiles to those simulated by the method of moments. In addition, this new equation is used to correlate several experiment data sets for verification, namely from ATRP of 2-hydroxyethyl methacrylate, methyl methacrylate, and N-isopropylacrylamide, showing better agreement than the existing equation. Although the equation derived here is strictly applicable to homogeneous (bulk and solution) normal ATRP, with further effort it may be extended to other types of ATRP as well as NMP and RAFT systems.

A Silver Bullet: Elemental Silver as an Efficient Reducing Agent for Atom Transfer Radical Polymerization of Acrylates

Elemental silver was used as a reducing agent in the atom transfer radical polymerization (ATRP) of acrylates. Silver wire, in conjunction with a CuBr(2)/TPMA catalyst, enabled the controlled, rapid preparation of polyacrylates with dispersity values down to Đ = 1.03. The silver wire in these reactions was reused several times in sequential reactions without a decline in performance, and the amount of copper catalyst used was reduced to 10 ppm without a large decrease in control. A poly(n-butyl acrylate)-block-poly(tert-butyl acrylate) diblock copolymer was synthesized with a molecular weight of 91 400 and Đ = 1.04, demonstrating good retention of chain-end functionality and a high degree of livingness in this ATRP system.