Kinetic Studies of Photopolymerization of Monomer-Containing Deep Eutectic Solvents

© 2020 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim The kinetics of photopolymerization in deep eutectic solvents (DESs) is investigated through real-time Fourier transform-infrared spectrometry (RT-FTIR). The systems of this study are choline chloride (ChCl) DESs made of acrylic acid and methacrylic acid (DES monomers) and a nonreactive analog isobutyric acid (IBA). The DES consisting of the analog also contains the monomer methyl methacrylate (MMA). Analysis of the evolution of conversion indicates dramatic increase in polymerization rate when comparing the polymerization of the DES monomers to pure monomer polymerization. A significant increase in polymerization rate is also seen in the systems that include a methyl ester derivative of the hydrogen bond donor monomer (e.g., MMA) in a nonpolymerizable DES (e.g., IBA−ChCl). It is proposed that the increased solvent viscosity, preorganization due to hydrogen bonding, and the polarity of the DES around the monomers play a role in the enhancement of the polymerization rate

Deep eutectic solvents as both active fillers and monomers for frontal polymerization

The deep eutectic solvents (DESs) based on the mixtures of a variety of ammonium salts and hydrogen bond donors containing acrylic acids and acrylamides are capable of sustaining frontal polymerization (FP). The selection of ammonium salt affects the reactivity and allows FP at relatively low temperature but with full conversion. Also, full conversion allows us to use these polymers for biomedical applications (e.g., drug delivery systems) as the unreactive ammonium salts can be released from the resulting polymer without by-products. We call these components >active fillers,> which can be ammonium salts with biological or pharmaceutical importance. For instance, we prepared poly(acrylic acid) loaded with lidocaine hydrochloride (a common anesthetic), the release of which was found to occur in a controlled fashion. The ammonium salts also create a sufficiently high viscosity to suppress buoyancy-driven convection without additional materials. The DES here described played an all-in-one role, providing the monomer, the active filler, and the polymerization medium for FPs. © 2013 Wiley Periodicals, Inc.Funded by: CONACYT. Grant Number: 181678.Peer Reviewe

Synthesis of biodegradable macroporous poly(l-lactide)/poly(ε-caprolactone) blend using oil-in-eutectic-mixture high-internal-phase emulsions as template

We have demonstrated that l-lactide (LLA) forms a eutectic mixture with ϵ-caprolactone (CL) in a 30:70 mol ratio with a melting point of -19 °C. Taking advantage of the liquid nature and polarity at the LLA-CL eutectic mixture, we have formulated oil-in-eutectic-mixture high-internal-phase emulsions (HIPEs) by stepwise addition of the oil phase (tetradecane) into the continuous phase (mixture of surfactant and LLA-CL eutectic mixture) at room temperature and under stirring. The oil-in-LLA-CL-eutectic-mixture HIPEs were polymerized in the presence of both the organocatalysts 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and methanesulfonic acid (MSA) and the initiator benzyl alcohol (BnOH) at 37 °C and without the addition of any extra reagent or solvent in one single pot. The catalytic selectivities of DBU and MSA for the ring-opening polymerizations of LLA and CL, respectively, allowed the synthesis of macroporous poly(l-lactide)/poly(ϵ-caprolactone) blend materials. The resulting materials exhibited a macroporous morphology that resembled that of the HIPE internal-phase droplets used as templates. These materials proved effective as oil absorbents for oil/water separation with not only a noticeable performance, similar to that of conventional sorbents in terms of both selectivity and recyclability, but also unprecedented safe disposability, certainly of interest for applications in the cleanup of industrial oily wastewaters and oil spills, thanks to the biodegradable features of both poly(ϵ-caprolactone) and poly(l-lactide)

Zinc-based deep eutectic solvent-mediated hydroxylation and demethoxylation of lignin for the production of wood adhesive

© 2016 The Royal Society of Chemistry. Choline chloride-ZnCl2 deep-eutectic solvent (ChCl-ZnCl2 DES), mole ratio 1:2, was used to improve the chemical reactivity of wheat straw alkali lignin under different temperatures and times of pretreatment. The chemical structure of the resulting modified lignin was studied by UV, FT-IR, 1H, 13C and 31P-NMR spectroscopies, TGA, NALDI-TOF MS and ICP. Interestingly up to 10 wt% of lignin can be readily dissolved in ChCl-ZnCl2 DES under the optimized pretreatment conditions (80 °C, 1 h) yielding ca. 65% of modified lignin upon precipitation using water as an antisolvent. As a result of the chemical modification of lignin occurring during its dissolution in DES, the total phenolic hydroxyl of the fraction precipitated increased ca. 1.9-fold while methoxyl moieties were reduced between 1.6 and 2.2-fold when compared with untreated lignin. Thus, in the fraction of lignin precipitated, phenolic hydroxyl formation took place at the expense of selective methoxyl cleavage from the aromatic ring, judging by the decrease of S units, whereas β-O-4′ linkages and molecular weight remain unchanged. Finally modified lignin was used as a phenol replacement in the synthesis of phenol-formaldehyde (PF) adhesives. Remarkably, the strength of the modified resin (1.3 MPa) compared with PF resin was practically the same when 40 wt% of the phenol was replaced by the modified lignin. This work shows that lignin can be readily modified in a DES-improving its reactivity-further advancing its prospective use in the wood industry

Synthesis of macroporous poly(acrylic acid)-carbon nanotube composites by frontal polymerization in deep-eutectic solvents

Deep Eutectic Solvents (DESs) formed between Acrylic Acid (AA) and Choline Chloride (CCl) exhibit certain properties of ionic liquids (e.g. high viscosity) that make them suitable for frontal polymerization (FP). The use of DESs not only as a monomer but also as the solvent prevents the use of additional solvents (i.e. typically of organic nature) and offers a green tool for the synthesis of functional composites. We have recently explored this approach for the preparation of poly(acrylic acid) (PAA) and poly(methacrylic acid). In this work, we have taken advantage of the outstanding capability of DESs to solubilize and/or disperse a number of substances to incorporate-in a homogeneous fashion-carbon nanotubes (in this particular case, N-doped MWCNT-CNxMWCNTs) in the polymerizable DES. Interestingly, CNxMWCNTs also played the role of an inert filler in FP. The resulting PAA-CNxMWCNT composites exhibited some distinct features as compared to previous PAA also obtained via DES-assisted FP. For instance, PAA-CNxMWCNT composites can undergo swelling depending on the pH, as bare PAA. However, the presence of CNxMWCNTs allows the formation of a macroporous structure after submission to a freeze-drying process, the achievement of which was not possible in bare PAA. The combination of structural (e.g. macroporosity) and functional (e.g. stimuli responsive) properties exhibited by these materials besides an eventually high biocompatibility-coming from the green character of the DES-assisted synthesis-should make the resulting macroporous PAA-CNxMWCNT composites excellent candidates for their future application as biomaterials. © 2013 The Royal Society of Chemistry.F. dM. acknowledges support from Grant reference numbers MAT2009-10214, MAT2011-25329,MAT2012-34811. P. Santiago acknowledges financial support from DGAPA-UNAM, through grant IN113411.Peer Reviewe

Identification of Subnanometric Ag Species, Their Interaction with Supports and Role in Catalytic CO Oxidation

The nature and size of the real active species of nanoparticulated metal supported catalysts is still an unresolved question. The technique of choice to measure particle sizes at the nanoscale, HRTEM, has a practical limit of 1 nm. This work is aimed to identify the catalytic role of subnanometer species and methods to detect and characterize them. In this frame, we investigated the sensitivity to redox pretreatments of Ag/Fe/TiO2, Ag/Mg/TiO2 and Ag/Ce/TiO2 catalysts in CO oxidation. The joint application of HRTEM, SR-XRD, DRS, XPS, EXAFS and XANES methods indicated that most of the silver in all samples is in the form of Ag species with size <1 nm. The differences in catalytic properties and sensitivity to pretreatments, observed for the studied Ag catalysts, could not be explained taking into account only the Ag particles whose size distribution is measured by HRTEM, but may be explained by the presence of the subnanometer Ag species, undetectable by HRTEM, and their interaction with supports. This result highlights their role as active species and the need to take them into account to understand integrally the catalysis by supported nanometals.We acknowledge support by the CSIC Open Access Publication Initiative through its Unit of Information Resources for Research (URICI).This research was supported by Government Program “Science” of Tomsk Polytechnic University, Grant No. 4.1187.2014/K, CONACYT Project 260409 and PAPIIT-UNAM Project IT200114 (Mexico), CSIC project 201480E077 and MINECO Project CTQ2013-41507-R (Spain). We gratefully thank O. Martynyuk, G. Torres Otañez, Z. I. Bedolla Valdez, E. Flores, F. Ruiz Medina, A. Olivas Sarabia, I. Gradilla, J. Mendoza, E. M. Aparicio Ceja, J. Peralta, David A. Domínguez, M. Sainz, R. Valdez Castro, M. Martínez, B. Acosta Ruelas, F. Ramírez Hernández and M. López Cisneros for valuable technical assistance

Free-radical polymerizations of and in deep eutectic solvents: Green synthesis of functional materials

© 2017 Elsevier B.V. The increasing environmental awareness has led to the search for alternative reaction media to reduce or eliminate the use of organic solvents in polymer science. Deep eutectic solvents (DESs), a subclass of ionic liquids, have emerged as sustainable solvents for a plethora of chemical reactions. In this Trend Article, DES utilization in free-radical polymerizations will be discussed. Two main fields of application are reported. In the first section, monomers able to undergo free-radical polymerization while taking part in a DES, as hydrogen bond donor or ammonium salt, so called DES monomers, are presented. In the second section, the role of DESs as solvents, where the polymerization takes place, either in the same phase or in an emulsion, is described. Finally, the properties of the polymers resulting from these particular methods of synthesis are discussed with emphasis on their green aspects

Low-Temperature and Solventless Ring-Opening Polymerization of Eutectic Mixtures of l-Lactide and Lactones for Biodegradable Polyesters

Biodegradability is one of the key features for reducing the negative environmental impact of plastic waste disposal; therefore, designing biocompatible polymeric biomaterials with programmable life cycles is urgently needed. Herein, deep eutectic solvent monomers (DESm) composed of l-lactide and various lactones of different molecular weights were formulated to obtain polyesters at low temperatures with the aid of organocatalysts and under solventless conditions. The introduced DESm expand the range of eutectic mixtures capable of undergoing ring-opening polymerization (ROP) to include mixtures of l-lactide with δ-valerolactone and δ-hexalactone. Extending the toolbox for DESm preparation will allow for the design of polyesters with tailored molecular weight and crystallinity, which are conducive to programmable degradability. ROP of DESm carried out at low temperatures and under solventless conditions holds promise for a sustainable framework for preparing biodegradable polymers for biomedical applications.</p

Polymerizable deep-eutectic solvents containing drugs produce drug delivery systems

Conference paper presented at European Congress and Exhibition on Advanced Materials and Processes (EUROMAT 2013), which took place in Sevilla (Spain) during 8-13th September 2013