Polymerizations and mechanistic studies have been performed to understand the kinetic pathways for the\ud
polymerization of the monomer oligo(ethylene oxide)\ud
monomethyl ether acrylate (OEOA) in aqueous media.\ud
Typically, the medium consisted of 18 wt % OEOA in\ud
water, in the presence of Cu catalysts coordinated by tris[2(dimethylamino)ethyl]amine (Me6TREN). Well-controlled\ud
polymerization of OEOA can be achieved in the presence of\ud
halide anions and Cu wire with≲600 ppm of soluble CuII\ud
species, rather than previously reported ca. 10 000 ppm of CuII and Cu0 particles formed by predisproportionation of CuI prior to monomer and initiator addition. The mechanistic studies conclude that even though disproportionation is thermodynamically favored in aqueous media, the SARA ATRP, not SET-LRP,\ud
mechanism holds in these reactions. This is because alkyl halides are much more rapidly activated by CuI than by Cu0\ud
(contribution of Cu0 to activation is <1%). Because of the high activity of CuI species toward alkyl halide activation,\ud
[CuI/Me6TREN] in solution is very low (<5μM) and classical ATRP equilibrium between CuI and CuII species is maintained.\ud
Although in aqueous media disproportionation of CuI/Me6TREN is thermodynamically favored over comproportionation, unexpectedly, in the presence of alkyl halides, i.e., during polymerization, disproportionation is kinetically minimized.\ud
Disproportionation is slow because its rate is proportional to [CuI/Me6TREN]2 and [CuI/Me6TREN] is very small. Thus, during polymerization, comproportionation is 104 times faster than disproportionation, and the ﬁnal thermodynamic equilibrium between disproportionation and comproportionation could be reached only after polymerization is completed. Activation of alkyl\ud
halides by CuI/Me6TREN in aqueous media occurs 8 orders of magnitude faster than disproportionation
Antimicrobial polymers represent a very promising class of therapeutics with unique characteristics for fighting microbial infections. As the classic antibiotics exhibit an increasingly low capacity to effectively act on microorganisms, new solutions must be developed. The importance of this class of materials emerged from the uncontrolled use of antibiotics, which led to the advent of multidrug-resistant microbes, being nowadays one of the most serious public health problems. This review presents a critical discussion of the latest developments involving the use of different classes of antimicrobial polymers. The synthesis pathways used to afford macromolecules with antimicrobial properties, as well as the relationship between the structure and performance of these materials are discussed.
Inorganic sulfites such as sodium dithionite (Na 2 S 2 O 4 ), sodium metabisulfite (Na 2 S 2 O 5 ), and sodium bisulfite (NaHSO 3 ) have been studied as reducing agents for atom transfer radical polymerization (ATRP). They act not only as very efficient reducing agents but also as supplemental activators for SARA (supplemental activator and reducing agent) ATRP of methyl acrylate in DMSO at ambient temperature. In combination with Cu(II)Br 2 /Me 6 TREN, they produced poly(methyl acrylate) with controlled molecular weight, low dispersity (M w /M n = 1.05), and well-defined chain-end functionality. Sulfites are eco-friendly, approved by FDA as food and beverage additives, and used commercially in many industrial processes.
Controlled/“living” radical polymerization
(CLRP) of vinyl chloride (VC) via the reversible addition–fragmentation
chain transfer (RAFT) process is reported for the first time. The
cyanomethyl methyl(phenyl)carbamodithioate (CMPCD) was found to be
an efficient RAFT agent enabling the CLRP polymerization of VC monomer
under certain experimental conditions. Two different radical initiators,
having very distinct half-life times at room temperature, were employed
in this study. The kinetic studies of RAFT polymerization of VC show
a linear increase of the molecular weight with the monomer conversion
and the lowest polydispersity (PDI) ever reported for poly(vinyl chloride)
(PVC) synthesized with CLRP method (PDI ∼ 1.4). The resulting
PVC was fully characterized using the matrix-assisted laser desorption
ionization time-of-flight mass spectrometry (MALDI-TOF-MS), 1H
nuclear magnetic resonance spectroscopy (1H NMR), and gel
permeation chromatography (GPC) techniques. The 1H NMR
and MALDI-TOF-MS analysis of PVC prepared via RAFT polymerization method
have shown the absence of structural defects and the presence of chain-end
functional groups. The “livingness” of the PVC was also
confirmed by a successful reinitiation experiment. The suitability
of the RAFT agent was also confirmed via high-level ab initio molecular orbital calculations.
The field of transition-metal-mediated controlled/"living" radical polymerization (CLRP) has become the subject of intense discussion regarding the mechanism of this widely-used and versatile process. Most mechanistic analyses (atom transfer radical polymerization (ATRP) vs. single-electron transfer living radical polymerization (SET-LRP)) have been based on model experiments, which cannot correctly mimic the true reaction conditions. We present, for the first time, a determination of the [Cu(I)Br]/[L] (L=nitrogen-based chelating ligand) ratio and the extent of Cu(I)Br/L disproportionation during CLRP of methyl acrylate (MA) in dimethylsulfoxide (DMSO) with Cu(0) wire as a transition-metal catalyst source. The results suggest that Cu(0) acts as a supplemental activator and reducing agent of Cu(II)Br(2)/L to Cu(I)Br/L. More importantly, the Cu(I)Br/L species seem to be responsible for the activation of SET-LRP.
This work contributes to the development of integrated lignocellulosic-based biorefineries by the pioneering exploitation of hardwood xylans by solubilization and extraction in deep eutectic solvents (DES). DES formed by choline chloride and urea or acetic acid were initially evaluated as solvents for commercial xylan as a model compound. The effects of temperature, molar ratio, and concentration of the DES aqueous solutions were evaluated and optimized by using a response surface methodology. The results obtained demonstrated the potential of these solvents, with 328.23 g L of xylan solubilization using 66.7 wt % DES in water at 80 °C. Furthermore, xylans could be recovered by precipitation from the DES aqueous media in yields above 90 %. The detailed characterization of the xylans recovered after solubilization in aqueous DES demonstrated that 4-O-methyl groups were eliminated from the 4-O-methylglucuronic acids moieties and uronic acids (15 %) were cleaved from the xylan backbone during this process. The similar M values of both pristine and recovered xylans confirmed the success of the reported procedure. DES recovery in four additional extraction cycles was also demonstrated. Finally, the successful extraction of xylans from Eucalyptus globulus wood by using aqueous solutions of DES was demonstrated.
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