Carlos M. R. Abreu

Ambient temperature rapid SARA ATRP of acrylates and methacrylates in alcohol–water solutions mediated by a mixed sulfite/Cu(II)Br2 catalytic system

The new generation of catalytic systems for Controlled/“Living” Radical Polymerization (CLRP) of vinyl monomers should be non-toxic, inexpensive and provide fast polymerizations in environmentally friendly media. Herein, we report the successful ambient temperature ATRP of several vinyl monomers (MA, n-BA, MMA and DMAEMA) catalyzed by inorganic sulfites (Na2S2O4 and Na2S2O5) and small amounts of a Cu(II)Br2/Me6TREN system in alcohol–water mixtures. The controlled character of ATRP of acrylates and methacrylates was confirmed by the linear increase of molecular weights with monomer conversion, narrow molecular weight distributions (Mw/Mn ∼ 1.05) and by reinitiation experiments (copolymerization and chain extension). 1H NMR and MALDI-TOF analyses confirmed the molecular structure and chain-end functionality of the obtained polymers. ATRP of MA using this novel catalytic system in alcohol–water mixtures with multifunctional Br-based initiators provides 4 and 6 arm star polyacrylates in a controlled manner without any observable gel formation. The data presented open up the possibility of using fast ATRP catalyzed by inorganic sulfites (approved by FDA as food and beverage additives) in solvents that are inexpensive, eco-friendly and widely used in chemical industrial processes.

Synergistic Effect of 1‑Butyl-3-methylimidazolium Hexafluorophosphate and DMSO in the SARA ATRP at Room Temperature Affording Very Fast Reactions and Polymers with Very Low Dispersity

An unusual synergistic effect between 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM-PF6) and dimethyl sulfoxide (DMSO) mixtures is reported for the supplemental activator and reducing agent atom transfer radical polymerization (SARA ATRP) of methyl acrylate (MA) using a catalytic system composed by sodium dithionate (Na2S2O4) and CuBr2/Me6TREN (Me6TREN: tris[2-(dimethylamino)ethyl]amine) at room temperature. To the best of our knowledge, the use of ionic liquids (IL) has never been reported for the SARA ATRP. The kinetic data obtained for a broad range of target molecular weights revealed very fast polymerization rates, low dispersity values (Đ < 1.05) and well-defined chain-end functionalities.

Getting faster: low temperature copper-mediated SARA ATRP of methacrylates, acrylates, styrene and vinyl chloride in polar media using sulfolane/water mixtures

Supplemental activator and reducing agent atom transfer radical polymerization (SARA ATRP) of acrylates, methacrylates, styrene and vinyl chloride was successfully performed in sulfolane/water mixtures using ppm amounts of soluble copper. The catalytic effect of the presence of water in the reaction mixtures resulted in a notable acceleration of the polymerization of the different monomers studied. The first-order kinetics with monomer conversion and the low dispersity values (Đ) of the polymers revealed the controlled features of the polymerization. As a proof-of-concept, an ABA block copolymer of poly(methyl acrylate)-b-poly(vinyl chloride)-b-poly(methyl acrylate) was prepared, confirming also the “living” character of the polymers. The results presented in this contribution extend the importance of sulfolane as an universal industrial solvent for the SARA ATRP of a broad range of monomer families by significantly enhancing the polymerization rate, due to the selective addition of water to the solvent mixture. The incorporation of small amounts of water in the solvent mixture has also allowed the use of FDA-approved sulfites as the SARA agent, which was not possible using pure sulfolane as the polymerization solvent.

Selective separation of Cr(III) and Fe(III) from liquid effluents using a chelating resin

This study aimed to assess the selective separation of Cr(III) from Fe(III) from liquid solutions by using a chelating ion exchange resin, Diaion CR 11, from Mitsubishi Chemical Corporation, in the H(+) form. Equilibrium experiments with synthetic solutions of iron and chromium were carried out in batch mode. For both metals favorable adsorption isotherms were obtained, and the experimental data were well described by the Langmuir model. However, the resin exhibited higher affinity for iron than for chromium. The regeneration experiments revealed that, for both metals, HCl provided higher removal efficiencies than H(2)SO(4) and HNO(3). Moreover, precipitation with NaOH allows selectively separate chromium and iron to be stripped from the resin. Experiments in fixed bed operation were carried out to assess the dynamic behavior of the sorption of Cr(III) and Fe(III) into the tested resin by using synthetic and industrial solutions. The experiments with industrial effluent showed that the resin can remove low levels of contaminant transition metal ions, and thus the effluent can be purified for reuse of chromium during periods of 20-25 min. The resin regeneration was achieved with a sequential treatment with HCl and NaOH/H(2)O(2). High efficiencies were observed for both monocomponent and multicomponent systems. A global strategy for separating and recovering Cr(III) from an effluent that also contains Fe(III) is presented, involving the integration of ion exchange (saturation and regeneration phases) and precipitation processes. In conclusion, our approach demonstrates that efficient separation of chromium and iron is possible if ion exchange operation in a fixed bed configuration is optimized and combined with conventional processes such as precipitation.

Mechanism of supplemental activator and reducing agent atom transfer radical polymerization mediated by inorganic sulfites: experimental measurements and kinetic simulations

The mechanism of atom transfer radical polymerization (ATRP) mediated by sodium dithionite (Na2S2O4), with CuIIBr2/Me6TREN as catalyst (Me6TREN: tris[2-(dimethylamino)ethyl]amine)) in ethanol/water mixtures, was investigated experimentally and by kinetic simulations. A kinetic model was proposed and the rate coefficients of the relevant reactions were measured. The kinetic model was validated by the agreement between experimental and simulated results. The results indicated that the polymerization followed the SARA ATRP mechanism, with a SO2•- radical anion derived from Na2S2O4, acting as both supplemental activator (SA) of alkyl halides and reducing agent (RA) for CuII/L to regenerate the main activator CuI/L. This is similar to the reversible-deactivation radical polymerization (RDRP) procedure conducted in the presence of Cu0. The electron transfer from SO2•-, to either CuIIBr2/Me6TREN or R-Br initiator, appears to follow an outer sphere electron transfer (OSET) process. The developed kinetic model was used to study the influence of targeted degree of polymerization, concentration of CuIIBr2/Me6TREN and solubility of Na2S2O4 on the level of polymerization control. The presence of small amounts of water in the polymerization mixtures slightly increased the reactivity of the CuI/L complex, but markedly increased the reactivity of sulfites.

Cyclopentyl methyl ether as a green solvent for reversible-addition fragmentation chain transfer and nitroxide-mediated polymerizations

Cyclopentyl methyl ether (CPME) was successfully used as an environmentally friendly alternative to the regularly employed organic solvents (e.g., tetrahydrofuran (THF), dimethyl sulfoxide (DMSO), dichloromethane (DCM) and dimethylformamide (DMF)) for the reversible-addition fragmentation chain transfer (RAFT) polymerization and nitroxide-mediated polymerization (NMP) of vinyl chloride (VC) and styrene (S). Methyl acrylate (MA) and vinyl acetate (VAc) were also successfully polymerized via RAFT using CPME. The kinetic data showed a linear increase of the molecular weight with the monomer conversion for both polymerization methods. The kappp data obtained in CPME were in the range of the values reported for THF, DMSO, DCM and DMF, while the final conversions were higher. The polymer samples were comprehensively characterized by 1H nuclear magnetic resonance spectroscopy (1H-NMR), 31P-NMR, matrix-assisted laser desorption ionization time-of-flight mass spectroscopy (MALDI-TOF-MS) and size exclusion chromatography (SEC). The “livingness” of the PVC macroinitiators prepared by RAFT and NMP were confirmed by chain-end characterization and successful reinitiation experiments. The data presented here prove that CPME is an excellent green substitute to avoid the use of toxic solvents for RAFT and NMP.

Reversible Deactivation Radical Polymerization of Vinyl Chloride

Poly(vinyl chloride) (PVC) is one of the higher consumed polymers (more than 40 million tons per year) and can only be prepared on an industrial scale by free-radical polymerization (FRP). Several intrinsic limitations of FRP have triggered interest in synthesizing this polymer by reversible deactivation radical polymerization (RDRP) methods. Despite the many achievements that have been made, the RDRP of nonactivated monomers, such as vinyl chloride (VC), presents several challenges to the scientific community. Several features of VC make its control by RDRP techniques particularly difficult. The most recent developments on RDRP of VC are critically discussed.