Β-ketoester Groups Research Articles

Reaction of β-Ketoester and 1,3-Diol to Access Chemically Recyclable and Mechanically Robust Poly(vinyl alcohol) Thermosets through Incorporation of β-(1,3-dioxane)ester.

The development of mechanically robust, chemically stable, and yet recyclable polymers represents an essential undertaking in the context of advancing a circular economy for plastics. Here, we introduce a novel cleavable β-(1,3-dioxane)ester (DXE) linkage, synthesized through the catalyst-free reaction of β-ketoester and 1,3-diol, to cross-link poly(vinyl alcohol) (PVA) for the formation of high-performance thermosets with inherent chemical recyclability. PVA, modified with β-ketoester groups through the transesterification reaction with excess tert-butyl acetoacetate, undergoes cross-linking reactions with the unmodified 1,3-diols within PVA itself upon thermal treatment. The cross-linking architecture improves PVA's mechanical properties, with Young's modulus and toughness that can reach up to 656 MPa and 84 MJ cm-3, i.e. approximately 3- and 12-fold those of linear PVA, respectively. Thermal treatment of the cross-linked PVA polymers under acid conditions leads to deconstruction of the networks, enabling the excellent recovery (>90 %) of PVA. In the absence of either thermal or acidic treatment, the cross-linked PVA maintains its dimensional stability. We show that the recovery of PVA is also possible when the treatment is performed in the presence of other plastics commonly found in recycling mixtures. Furthermore, PVA-based composites comprising carbon fibers and activated charcoal cross-linked by the DXE linkages are also shown to be recyclable with recovery of the PVA and the fillers.

High-Throughput Preparation of Antibacterial Polymers from Natural Product Derivatives via the Hantzsch Reaction.

SummaryThe Hantzsch and free-radical polymerization reactions were combined in a one-pot high-throughput (HTP) system to simultaneously prepare 30 unique polymers in parallel. Six aldehydes derived from natural products were used as the starting materials to rapidly prepare the library of 30 poly(1,4-dihydropyridines). From this library, HTP evaluation methods led to the identification of an antibacterial polymer. Mechanistic studies revealed that the dihydropyridine group in the polymer side-chain structure plays an important role in resisting bacterial attachment to the polymer surface, thus leading to the antibacterial function of this polymer. This research demonstrates the value of multicomponent reactions (MCRs) in interdisciplinary fields by discovering functional polymers for possible practical applications. It also provides insights to further developing new functional polymers using MCRs and HTP methods with important implications in organic chemistry, polymer chemistry, and materials science.

β-ketoester-functionalized magnetoactive electrospun polymer fibers as Eu(III) adsorbents

Blended polymer fibers based on a hydrophobic random copolymer having β-ketoester metal ion binding functionalities namely poly(methyl methacrylate)-random-poly(2-(acetoacetoxy) ethyl methacrylate) (PMMA-co-PAEMA) and the hydrophilic polyethylene oxide (PEO) were fabricated by electrospinning and further evaluated for the first time as adsorbents for the removal of Eu(III) from aqueous media. Moreover, magnetoactive fibrous analogues were prepared by incorporating preformed, oleic-acid coated Fe3O4 NPs within the polymer fibers during electrospinning. The Eu(III) adsorption was investigated as a function of pH and initial metal ion concentration whereas the effect of the Fe3O4 NPs and of the β-ketoester groups on the membrane adsorption efficacy was also investigated. The experimental data, which were well fitted by the Langmuir isotherm model, indicated increased affinity with increasing pH and reached maximum values (~ 95%) at pH 6.5. The presence of the β-ketoester functionalities as well as the incorporation of the Fe3O4 nanoparticles within the fibrous adsorbents affect positively the adsorption process and indicate the significance of chemical modification with respect to water purification and precious metal recovery using adsorbent-based technologies.

Postpolymerization Modification of Poly(dihydropyrimidin-2(1H)-thione)s via the Thiourea-Haloalkane Reaction to Prepare Functional Polymers.

A highly reactive thiourea-contained polycondensate, poly(dihydropyrimidin-2(1H)-thione) (poly(DHPMT)) has been facilely synthesized via the Biginelli polycondensation using thiourea and a difunctional compound containing benzaldehyde and β-keto ester groups as monomers. The thiourea moiety in the polymer structure has similar reactivity as the thiourea, thus the poly(DHPMT) is an excellent polymer precusor for preparing new functional polymers through the postpolymerization modification (PPM) strategy. After simple reaction with functional haloalkanes, the parent poly(DHPMT) could be almost completely converted (>99%) to daughter polymers containing alkene or alkyne side groups. Then, the daughter polymers have been further transferred to granddaughter polymers through another PPM via thiol-ene or Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reactions. Besides, when 3-phenylpropargyl chloride was used as the reactant, a bright yellow fluorescent polymer could be simply achieved due to the in situ formed conjugated heterocycle in the polymer structure, further demonstrating the diversity of the functional polymers through PPM. Considering the easily available monomers, simple polycondensation, and the excellent reactivity of the thiourea moiety in the polymer structure, this thiourea-contained Biginilli polycondensate might be a versatile platform for new functional polymer preparation.

Palladium-based micellar nanohybrids: preparation and nonlinear optical response

In the present work the synthesis and physicochemical characterisation of a new class of Pd-containing micellar nanohybrid systems are presented. The new systems consist of metallic Pd nanoparticles and well-defined diblock copolymers, possessing carbazole and β-ketoester side-chain functionalities, namely poly[2-(N-carbazolyl) ethyl methacrylate]-block-poly[2-(acetoacetoxy) ethyl methacrylate] (CbzEMAx-b-AEMAy). Block copolymer synthesis has been carried out by Reversible Addition–Fragmentation chain Transfer (RAFT) polymerisation. The presence of the β-ketoester groups within these diblock copolymers enabled the complexation and stabilisation of the Pd nanoparticles in tetrahydrofuran. Visualisation of the Pd-containing micellar nanohybrids was realised by means of transmission electron microscopy (TEM), providing information on the metal nanoparticle sizes. The nonlinear optical response of these polymer–metal nanohybrid systems has been systematically studied both in solution and in thin films, using the Z-scan technique, employing 35 ps, visible (532 nm) and infrared (1064 nm) laser excitation. Discussion in regards to the spectral position of the surface plasmon resonance (SPR) of the Pd nanoparticles and its effect on the nonlinear optical response of the micellar systems has been carried out in terms of a two-photon process.

A rapid and diverse construction of 6-substituted-5,6-dihydro-4-hydroxy-2-pyrones through double Reformatsky reaction

A rapid and diverse synthesis of biologically important 6-substituted-5,6-dihydro-4-hydroxy-2-pyrones through a double Reformatsky reaction of aldehydes to δ-hydroxy-β-ketoesters followed by lactonization is described. Due to the high functional group tolerance and reaction site discrimination between aldehyde, nitrile, and ester groups in the substrate, the protocol can provide the dihydropyrones with bromo, nitro, carboxylic acid, and β-ketoester groups, which are suitable for the further derivatizations. Furthermore, the protocol has been successfully applied to the rapid total synthesis of naturally occurring Yangonin.

Nanofibrillation of alkyl ketene dimer (AKD)-treated cellulose in tetrahydrofuran

A hardwood bleached kraft pulp (HBKP) was reacted with alkyl ketene dimer (AKD) under solvent-free and heterogeneous conditions, and a fibrous chloroform-insoluble fraction with a degree of substitution of AKD β-ketoester groups of 0.75 was obtained at a weight ratio of 95 % of the total reaction product. When this AKD-treated and CHCl3-insoluble HBKP was mechanically disintegrated in tetrahydrofuran, the suspension turned to a viscous and translucent gel. When an unfibrillated fraction was removed by filtration using a glass filter with 40 μm pore size, the weight recovery ratio of the filter-passed fraction was approximately 30 %. Scanning and transmission electron microphotographs of the glass filter-passed fraction showed that this fraction consisted of cellulose nanofibrils more than several micrometers in length, the surfaces of which probably had AKD β-ketoesters in high densities.

Coordination Behavior of Acetoacetate Ligands with Attached Methacrylate Groups Containing Alkyl-Spacers of Different Length to Titanium and Zirconium Alkoxides

Metal-alkoxides containing polymerizable groups are regularly used as precursors for inorganic–organic hybrid materials applying the combination of the sol–gel process and organic polymerizations. Here we report the synthesis of acetoacetoxy derivatives that are linked to methacrylate groups via alkyl chains of different chain length. The coordination of the resulting molecules to titanium- and zirconium-alkoxides (M(OR)4; M = Ti, Zr; R = ethyl, butyl, isopropyl) was investigated applying NMR and FT-IR measurements. The results were related to structural data of the dinuclear complex [Ti(O i Pr)3(EAA)]2 (HEAA: ethyl acetoacetate) which was obtained by single crystal X-ray diffraction. The study revealed that the β-keto ester groups acted as chelating ligands in all cases and thus polymerizable coordination compounds were formed. However, NMR analyses in solution showed that transesterification of the methacrylic-type monomers occurred even at mild conditions as a side reaction in a ratio which was found to be dependent on the type of metal alkoxide used.

Photocured polymer networks based on multifunctional ?-ketoesters and acrylates

The objects of this study are highly crosslinked networks. The base-catalyzed Michael reaction of β-ketoesters with vinyl groups of the pentaerythritol tetra-acrylate (PETA) was used for a step grow formation of the crosslinked polymer in dark. The nonreacted vinyl groups and vinyl monomer were built up to the network structure by photopolymerization in the second step of synthesis. An analysis of crosslinked polymers shows that the long spacer between β-ketoester groups in propylenglycol-425-diacetoacetate (PGDAA) favors an extent of reaction compared to pentaerythritol tetrakis (acetoacetate) (PETAA). The excess of vinyl monomers added to polymerization batch functions in the first step of the synthesis as a reactive solvent [triethylene glycol dimethacrylate (TEGDMA); PETA]. The dissolution of reactants has a positive effect on homogeneity, conversion, and crosslink density of prepared networks. The consumption of reactive groups in a course of the network formation, the crosslink density, and dynamic mechanical properties of the prepared networks were determined from Fourier transform infrared (FTIR) spectroscopy, differential scanning calorimetry (DSC), sol-gel analysis, dynamic testing, and stress-strain dependencies. The dynamic testing indicates that the networks synthesized in two steps from batches containing an excess of vinyl monomer consist from two highly crosslinked phases interpenetrating each other. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65: 165–178, 1997

Novel synthesis of low VOC polymeric dispersions and their application in waterborne coatings

A new approach for the synthesis of reactive solvent-free polyurethane dispersions is discussed in detail. A powerful tool is introduced by incorporating β-ketoester groups in the polymer chain. β-Ketoesters have two different reaction sites. On the one hand the keto groups can react with nucleophiles like polyamines. On the other hand the carbon atoms of the activated CH 2 groups are centers for the attack of electrophiles like aldehydes and isoyanates. Polymers functionalized in this way are interesting new intermediates in chain extension reactions for aqueous polyurethane dispersions. Another advantage of the functionalized polyurethane dispersions is the possibility of additional crosslinking with melamine resins or blocked isocyanates.

Polyene cyclizations using mercury (II) triflate-N,N-dimethylaniline complex - participation by internal nucleophiles

The cyclization of a number of functionalized polyenes with mercuric triflate - N,N-dimethylaniline complex (Nishizawa's reagent) to give bicyclic or tricyclic products has been studied. Suitably positioned internal nucleophiles, such as carbonyl, hydroxy and β-ketoester groups were found to participate to varying extent, in the termination of these cyclizations.

Relative reactivities of amylose hydroxyl groups in the reaction with diketene

13C nuclear magnetic resonance (n.m.r.) spectra at 75.4 MHz of partially modified amylose with β-keto ester groups (degree of substitution ( DS) ranging from 0.52 to 2.42) were studied in order to evaluate the selectivity of the reaction of amylose with diketene in the homogeneous phase. Analysis of the spectra of ring carbons in the anhydroglucose units shows that the reactivity of individual hydroxyl groups decreases in the order C-6>C-3>C-2 for DS values up to ∼1.8. For higher DS values a negative deviation is observed for the hydroxyl group at C-6 and a positive deviation for the hydroxyl groups at C-2 and C-3. The DS values determined by 13C n.m.r. spectra are in good agreement with those found by chemical analysis.

SELECTIVE α-OXIDATION OF CYCLIC β-KETOESTERS WITH POTASSIUM FLUORIDE AND OXYGEN IN DIMETHYL SULFOXIDE: A SYNTHESIS OF KJELLMANIANONE

Abstract Selective oxidation of cyclic β-ketoester groups with potassium fluoride-oxygen in dimethyl sulfoxide provided α-hydroxy-β-ketoesters in fair yields. Application of the oxidation to 5-methoxycarbonyl-3-methoxy-cyclopent-2-enone furnished (±)-kjellmanianone.

Chemistry of amino acids. VII. The synthesis and spectral studies of some 2-piperidones bearing beta-keto ester groups.

Some 2-piperidones (IX and X) bearing β-keto ester groups were synthesized from the methyl esters (V) of alanine and phenylalanine according to a route similar to that described in our previous paper. Spectral studies (infrared, ultraviolet and nuclear magnetic resonance) revealed that these β-keto esters (IX and X) mainly exist in the chelated enolic tautomer (E) both in the solid state and in solution. The NMR spectra of some indole derivatives (XI-XVI) were also investigated.