Bispropargyl Ether Research Articles

Fumarate metal organic frameworks as reactive and curing reaction alternant in hydrophobic bispropargyl ether based matrix resin system

Fumarate metal organic frameworks as reactive and curing reaction alternant in hydrophobic bispropargyl ether based matrix resin system

3D Printing of Dual‐Cure Networks Based on (Meth)acrylate/Bispropargyl Ether Building Blocks

In recent years, dual‐cure chemistry has been exploited to realize interpenetrating networks (IPNs) that provide enhanced thermo‐mechanical properties. In this contribution, photoinduced curing of (meth)acrylates is used to build the desired 3D structure, whereas the thermally triggered polymerization reaction of 2H‐chromene functionalized building blocks is utilized to create the IPN. This strategy combines the advantages of traditional UV‐curable monomers with high‐performance thermosets. After the successful synthesis of the bispropargyl ether derivative, i.e., 4,4′‐(propane‐2,2‐diyl)bis((ethynyloxy)benzene), its thermally induced conversion to the corresponding 2H chromene functionalized prepolymer is studied by Fourier‐transform infrared spectroscopy and gel permeation chromatography. The network formation as well as the printability of various formulations containing different amounts of the thermo‐curable building block is investigated. The obtained IPNs provide enhanced thermo‐mechanical properties making these resins suitable for the additive manufacturing of functional 3D parts for high‐performance applications.

Synthesis of Isohexide Diyne Polymers and Hydrogenation to Their Saturated Polyethers.

The incorporation of renewable feedstocks into polymer backbones is of great importance in modern polymer science. We report the synthesis of 1,3-diyne polymers derived from the bispropargyl ethers of isosorbide, isomannide, and isoidide. The dialkyne monomers can be polymerized through an adaptation of the Glaser-Hay coupling using a nickel(II) cocatalyst. These well-defined diyne polymers bear an iodoalkyne end group, afforded through an unanticipated reductive elimination pathway, and display glass transition temperatures (Tg) from 55 to 64 °C. Fully saturated, analogous polyethers can be prepared from the hydrogenation of the diyne polymers, and these show Tg values between -10 and -2 °C. Both the 1,3-diyne polymers and the saturated analogues display similar trends in their Tg values vis-à-vis the stereochemical features of the isohexide unit within the backbone. This polymerization provided access to two series of isohexide-based polyethers, the thermal properties of which are influenced by the nature of the 2,4-hexadiynyl and hexamethylene linkers as well as the relative configuration of the bicyclic subunit in the backbone. The reported method represents an important step toward accessing well-defined polyethers from renewable feedstocks using readily available catalysts and convenient ambient conditions.

Thermal and Mechanical Properties of Triazole Cross‐Linked Glycidyl Azide (GAP) and Azido Polycarbonate Networks

AbstractTriazole cross‐linked energetic polymer networks obtained from the reaction of dialkyne curing agents with glycidyl azide polymers (GAP) or poly(2,2‐[bisazidomethyl]propane‐1,3‐diyl carbonate) (poly[BAMPC]) were studied, and their thermal and mechanical properties are reported. The dialkynes studied include bis(propargyl)ether (BPE), bis(propargyl)malonate (BPM), and 4,4’‐diacyanohepta‐1,6‐diyne (DCHD), three compounds previously described as curing agents for glycidyl azide pre‐polymers. The cured polymer networks display a wide range of properties dependent on the nature of the azido pre‐polymer, the nature of the dialkyne, the alkyne/azide molar ratio, and the molecular weight of the pre‐polymer used. Results confirm that the three dialkynes are effective curing agents able to form rigid networks out of either pre‐polymer and that the lighter molecular weight BPE and DCHD both improve mechanical properties of cured networks with less dilution of the system's energetic content. Triazole cross‐linked poly(BAMPC) networks were studied for the first time, and promising physical and mechanical properties are reported.

Azide telechelics chain extended by click reaction: Synthesis, characterization, and cross‐linking

Azide telechelics of poly(dimethylsiloxane) (PDMS), polypropylene oxide (PPO), and polyethylene oxide (PEO) were synthesized from the corresponding epoxy telechelics and characterized. These oligomeric azides were chain extended by reaction with bispropargyl ether of bisphenol A (BPEBA) through a copper‐catalyzed azide‐alkyne cycloaddition (CuAAC) reaction. PDMS manifested a faster reaction in contrast to PPO or PEO. The chain‐extended polymers underwent cross‐linking above 170°C through thermal cleavage of residual (terminal) azide groups. This was manifested in their rheograms and was further substantiated by FTIR and NMR spectroscopic analyses. Dynamic mechanical analyses of the cross‐linked polymers exhibited characteristic transitions of hard and soft segments, implying microphase separation in the system. Microscopic evaluation of the thermally cross‐linked sample revealed a porous morphology with microsized to nanosized pores.

Synthesis of furan-fused 1,4-dihydrocarbazoles via an unusual Garratt-Braverman Cyclization of indolyl propargyl ethers and their antifungal activity

The reactivity of indole based bis-propargyl ethers 4a-4g under Garratt-Braverman condition (KOBut in refluxing toluene) has been studied. Interestingly, these propargyl systems with one arm attached with substituted 3-indolyl derivatives leaving the other arm unsubstituted produced the 3,4-furan fused dihydrocarbazole derivatives 6a-6g (and not the expected carbazole derivatives) as the predominant product (70–82%) making this methodology to access such derivatives an attractive route. The results are supported by computational studies and some of the carbazole derivatives showed good antifungal activities.

Copper salt–assisted polymerization of bispropargyl ether–bismaleimide blend

Bispropargyl ether (BPE) of bisphenol-A was prepared. It was blended with 4,4’-bismaleimido diphenyl methane (BMI, 0.5:0.5 mol). The copper sulphate pentahydrate (CuSO4·5H2O) was blended (1% w/w) separately with pure BPE and BPE-BMI blend and the materials were thermally cured. The structural characterization of the materials was done using a Fourier-transform infrared spectrophotometer. The curing behaviour of the materials was investigated using differential scanning calorimetry. The presence of copper salt in BPE shifted the curing temperature to lower temperature region. The presence of copper salt in BPE-BMI blend also decreased the curing onset temperature by approximately 15°C. The thermal property of the polymers was investigated using thermogravimetry. The incorporation of copper salt in BPE-BMI blend led to polymer with increased thermal stability.

Does the Mechanism of the Garratt-Braverman Cyclization Differ with Substrates? A Computational Study on Bispropargyl Sulfones, Sulfides, Ethers, Amines, and Methanes.

We studied the variation in mechanism among different bispropargyl substrates-sulfone, sulfide, ether, amine, and methane-toward Garratt-Braverman (GB) cyclization using density functional theory calculations. Isomerization and cycloaddition are the key steps in the GB cyclization. To compare the reactivity among the various substrates, we computed the free energy of activation (ΔG(⧧)) for the cycloaddition and the cyclization steps, whereas we used the theoretically computed pKa values for the isomerization steps. Our results suggest that the sulfones undergo a relatively fast isomerization followed by slower cyclization, while the ethers undergo a slow isomerization followed by easy cyclization. The methanes and amines are similar to the ethers, and the sulfides showed intermediate behavior. We extended our study to unsymmetrical substrates and compare the results with experiments that suggest the isomerization to be the rate-limiting step for bispropargyl ethers, while cyclization through a diradical intermediate is crucial to the rate for the bispropargyl sulfones. On the basis of these findings, we made predictions on the selectivity of unsymmetrical bispropargyl sulfones, amines, methanes, and sulfides. This is the first detailed mechanistic study on the GB cyclization of bispropargyl substrates other than sulfones.

ChemInform Abstract: Shifting the Reactivity of Bis‐propargyl Ethers from Garratt—Braverman Cyclization Mode to 1,5‐H Shift Pathway to Yield 3,4‐Disubstituted Furans: A Combined Experimental and Computational Study.

Aryl or vinyl substituted bis-propargyl ethers upon base treatment generally form phthalans via the Garratt–Braverman (GB) cyclization pathway. In a major departure from this usual route, several aryl/vinyl bis-propargyl ethers with one of the acetylenic arms ending up with 2-tetrahydropyranyloxy methyl or ethoxy methyl have been shown to follow the alternative intramolecular 1,5-H shift pathway upon base treatment. The reaction has led to the formation of synthetically as well as biologically important 3,4-disubstituted furan derivatives in good yields. The initially formed E isomer in solution (CDCl3) slowly isomerizes to the Z isomer, indicating greater stability of the latter. The factors affecting the interplay between the 1,5-H shift and GB rearrangement have also been evaluated, and the results are supported by DFT-based computational study.

ChemInform Abstract: C—H Insertions in Oxidative Gold Catalysis: Synthesis of Polycyclic 2H‐Pyran‐3(6H)‐ones via a Relay Strategy.

AbstractFunctionalized bicyclic or polycyclic pyranones are obtained by a cascade cyclization and subsequent C—H insertion starting from easily accessible bispropargyl ethers.

ChemInform Abstract: Synthesis of Phthalides from Bis‐propargyl Ethers: Use of Garratt—Braverman Cyclization to Construct the Phthalans and IBX as a New Reagent for Subsequent Oxidation.

An efficient route to phthalides is described starting from easily available bis-propargyl ethers. The method involves Garratt–Braverman cyclization of the ethers to phthalans which are then efficiently oxidized to the phthalides by iodoxy benzoic acid (IBX) which has been shown to be a superior reagent in terms of yield and reagent stoichiometry for such a transformation in comparison with more commonly used KMnO4/CuSO4 reagent.

Thermal degradation kinetics of structurally diverse poly(bispropargyl ethers-bismaleimide) blends

Structurally diverse bispropargyl ethers using resorcinol, quinol, 4,4′-dihydroxy biphenyl, bisphenol-A, 4,4′- dihydroxy diphenyl ketone, 4,4′-dihydroxy diphenylsulphone, trimethyl indane bisphenol and tetramethyl spirobiindane bisphenol were prepared by using phase transfer catalyst. Synthesized materials were separately blended with 4,4′-bismaleimido diphenyl methane (BMIM) in mole ratios (0.5:0.5). The materials were thermally cured and the structural characterisation and the thermal properties of these cross-linked materials are investigated using Fourier-transform infrared (FTIR) spectrophotometer and thermogravimetric analyzer (TGA). Among the different materials investigated polyMRPE, polyMBPEBPA and polyMSPE show higher onset degradation temperature of 300 °C indicating higher thermal stability. The degradation kinetics is investigated using Flynn-Wall-Ozawa (FWO), Vyazovkin (VYZ) and Friedman (FRD) methods. Amongst the various cured materials investigated, the activation energy (Ea-D) values obtained for polyMRPE and polyMKPE were observed to increase continuously from α = 0.2 to 0.8 and the values range from 199 kJ/mol to 245 kJ/mol and 153 kJ/mol to 295 kJ/mol respectively. The crosslinked materials resulting from these bispropargyl monomers definitely need more energy for bond cleavage due to the presence of more aromatic units. The volatile products obtained during the thermal degradation of the polymers were analyzed using thermogravimetric-Fourier transform infrared analyses (TG-FTIR). The phenols, substituted phenols, carbon monoxide, carbon dioxide and small amount of aniline were found to be the major products during thermal degradation of these cured blends.

Shifting the Reactivity of Bis-propargyl Ethers from Garratt-Braverman Cyclization Mode to 1,5-H Shift Pathway To Yield 3,4-Disubstituted Furans: A Combined Experimental and Computational Study.

Aryl or vinyl substituted bis-propargyl ethers upon base treatment generally form phthalans via the Garratt-Braverman (GB) cyclization pathway. In a major departure from this usual route, several aryl/vinyl bis-propargyl ethers with one of the acetylenic arms ending up with 2-tetrahydropyranyloxy methyl or ethoxy methyl have been shown to follow the alternative intramolecular 1,5-H shift pathway upon base treatment. The reaction has led to the formation of synthetically as well as biologically important 3,4-disubstituted furan derivatives in good yields. The initially formed E isomer in solution (CDCl3) slowly isomerizes to the Z isomer, indicating greater stability of the latter. The factors affecting the interplay between the 1,5-H shift and GB rearrangement have also been evaluated, and the results are supported by DFT-based computational study.

Synthesis of phthalides from bis-propargyl ethers: use of Garratt–Braverman cyclization to construct the phthalans and IBX as a new reagent for subsequent oxidation

An efficient route to phthalides is described starting from easily available bis-propargyl ethers. The method involves Garratt–Braverman cyclization of the ethers to phthalans which are then efficiently oxidized to the phthalides by iodoxy benzoic acid (IBX) which has been shown to be a superior reagent in terms of yield and reagent stoichiometry for such a transformation in comparison with more commonly used KMnO4/CuSO4 reagent.

Mechanistic and kinetic aspects of the curing of phthalonitrile monomers in the presence of propargyl groups

The influence of propargyl groups on the thermal polymerization of phthalonitrile groups has been examined through reaction of a blend of a bisphthalonitrile viz. 2,2-bis(4-phthalonitrile oxy phenyl)propane and a bispropargyl ether viz. 2,2-bis(4-proparyloxy phenyl)propane (BPhPR). The possibilities for co-reaction of the propargyl and phthalonitrile moieties and/or the catalytic nature of the cure reaction prevailing in their blends were indicated by multiple exotherms in differential scanning calorimetry and dynamic rheological experiments. These have been attributed to homopolymerization of propargyl, hydroxyl and chromene mediated nitrile polymerization. FT-IR and fluorescence emission spectroscopic investigations on model compounds confirmed that nitrile polymerization was favoured by the chromene and hydroxyl groups formed by Claisen rearrangement. Activation energy of the reaction step involving chromene mediated phthalonitrile crosslinking was found to be 89 kJ/mol which was close to the value of phenol catalysed phthalonitrile curing.

Reversal of regioselectivity in acetylation and deacetylation of aryl-naphthalene diols and diacetates by Amano lipase

The regioselectivity of hydrolysis by Amano lipase (AK lipase) from Pseudomonas fluorescens of aryl naphthalene 4′,7-diacetates 1a–c prepared by the Garratt–Braverman cyclization of bis-propargyl sulfones, ethers and sulfonamides and acetylation of the corresponding diol 2a–c were studied. In all of these cases, the selectivity of both hydrolysis and acetylation were excellent. However, the pattern of selectivity was found to be dependent upon the nature of the fused heterocyclic ring, namely, dihydrothiophene dioxide (sulfolene), dihydrofuran (phthalan) or dihydro isoindole (indoline). For the isoindole system, the hydrolysis as well as the acetylation occurred at C-7, whereas for the furan derivative, the reaction took place entirely at C-4′. Interestingly, for dihydrothiophene dioxide, reversal of selectivity was observed in hydrolysis and acetylation. The results are in contrast with those reported for similar reactions on aryl naphthalene 2′,5-diacetates and corresponding diols. The observed results can be explained by molecular docking using PCL crystal structure, representing the Pseudomonas lipase family.

Bismaleimide and bispropargyl ether blends: Curing kinetics—Model free approach

Two structurally different bismaleimides, namely 2,2-bis[4-(4-maleimidophenoxy-phenyl)]propane (BMIX) and 5(6)-maleimide-1(4′-maleimidophenyl)-1,3,3′-trimethyl indane (BMII) and bispropargyl ether of bisphenol A (BPEBPA) were prepared. The two bismaleimides were separately blended with BPEBPA in different mole ratios [BMIX/BMII: BPEBPA = 100: 0, 75: 25, 50: 50, 25: 75, 0: 100%] and the materials were thermally polymerized at 230°C. The curing studies of the monomers and blends reveal that the blending of BMIX and BMII with BPEBPA decreases the curing temperature window. Blending of 25% of either BMIX or BMII with BPEBPA drastically reduces the curing enthalpy and was nearly half the value of pure BPEBPA. The FTIR spectra of the cured materials show that the chromene ring stretching frequency of BPEBPA decreases as the bismaleimide content increases and new absorption peaks corresponding to cyclopentane (941 cm−1) and cyclohexane (1018 cm−1) appeared. The curing kinetics of the monomers and blends were studied using three model free kinetic methods. The trend noted for the variation of apparent activation energies for curing of 25% BMIX + 75% BPEBPA blend is different compared to the monomers and other blends.

ChemInform Abstract: Selectivity in Garratt—Braverman Cyclization of Aryl‐/Heteroaryl‐Substituted Unsymmetrical Bis‐Propargyl Systems: Formal Synthesis of 7′‐Desmethylkealiiquinone.

Unsymmetrical bis-propargyl ethers and sulfonamides containing various combinations of aryl/heteroaryl substituents at the acetylene termini were synthesized, and their reactivity under basic conditions was studied. Moderate to high (chemo)selectivity was observed, which followed a trend opposite to that reported earlier for the corresponding sufones. The major products obtained in most cases (except with indole) were formed via participation of the heteroaryl ring or the less electron rich aryl ring. The selectivity observed in imidazole-based systems was exploited to complete a formal total synthesis of 7′-desmethylkealiiquinone, an analogue of the marine alkaloid kealiiquinone.

Selectivity in Garratt–Braverman Cyclization of Aryl-/Heteroaryl-Substituted Unsymmetrical Bis-Propargyl Systems: Formal Synthesis of 7′-Desmethylkealiiquinone

Unsymmetrical bis-propargyl ethers and sulfonamides containing various combinations of aryl/heteroaryl substituents at the acetylene termini were synthesized, and their reactivity under basic conditions was studied. Moderate to high (chemo)selectivity was observed, which followed a trend opposite to that reported earlier for the corresponding sufones. The major products obtained in most cases (except with indole) were formed via participation of the heteroaryl ring or the less electron rich aryl ring. The selectivity observed in imidazole-based systems was exploited to complete a formal total synthesis of 7'-desmethylkealiiquinone, an analogue of the marine alkaloid kealiiquinone.

High-temperature matrix resins based on bispropargyl ethers (BPEs) – part 2

Structurally diverse bispropargyl ethers (BPEs) using resorcinol, quinol, 4,4′-dihydroxy biphenyl, bisphenol-A, 4,4′-dihydroxy diphenyl ketone, 4,4′-dihydroxy diphenylsulphone, trimethyl indane bisphenol and tetramethyl spirobiindane bisphenol were synthesized, and it was separately blended with 4,4′-bismaleimido diphenyl methane (BMIM) in mole ratios (0.5:0.5). The structural characterizations of the materials are carried out using Fourier transform infrared and nuclear magnetic resonance studies. Differential scanning calorimetric analysis shows that the difference in the melting characteristics and decrease in the curing window for different BPEs were caused by the incorporation BMIM. Addition of BMIM to BPEs reduces the heat liberated during the thermal curing. The curing kinetics is investigated using Flynn–Wall–Ozawa, Vyazovkin and Friedman methods. Amongst the various BPEs investigated, the activation energy ( Ea) values obtained from spirobiindane BPE (SPIPE) behaves entirely in a different manner compared to all other materials investigated. The apparent Ea values for SPIPE was observed to increase with increasing extent of reaction up to 0.2–0.5 and then the Ea values decrease with increasing extent of reaction up to 0.55–0.8. The Ea for the polymer blends obtained by the incorporation of BMIM with different BPEs shows nearly linear increase in the Ea value, and the rate of increase is influenced by the structure of the aromatic spacer present in between the propargyl groups.