Cyclohexene Carbonate Research Articles

All-Polycarbonate Graft Copolymers with Tunable Morphologies by Metal-Free Copolymerization of CO2 with Epoxides

Brush-type macromolecules (BMs) have attracted much attention over the past decades because of their unique properties and potential applications in nanoscience, drug-delivery systems, and photonics. A two-step strategy of synthesis of polycarbonate-grafted copolymers with either star-shaped or brush-typed morphologies using a “grafting from” approach is reported; the backbone in these all-polycarbonate graft copolymers is made of poly(cyclohexene carbonate) (PCHC), and the side grafts are made of poly(propylene carbonate) (PPC). In the first step, poly (vinyl-cyclohexene carbonate) (PVCHC) backbones of two different sizes (PVCHC35, PVCHC283) were prepared by copolymerization of vinyl-cyclohexene oxide (VCHO) with CO2 in the presence of triethylborane (TEB), using tetrabutyl ammonium succinate (TBAS) as the initiator. In the second step, the dangling vinyl double bonds of PVCHC were transformed into carboxylic acid groups. After partial neutralization of the latter using tetrabutyl ammonium hydroxide, the PPC grafts could be grown from the backbone carboxylic sites by copolymerization of propylene oxide (PO) with CO2 in the presence of TEB. Before attempting the synthesis of the above all-polycarbonate grafted copolymers, we check the viability of the above synthetic strategy by preparing graft copolymers made of a polymethacrylate backbone and PPC side grafts. In the latter case, the backbone was generated by reversible addition–fragmentation chain-transfer (RAFT) polymerization of methacrylic acid (MAA), followed by the growth of PPC side grafts using the backbone carboxylates as initiating sites. In both cases (PVCHC-g-PPC and PMAA-g-PPC), two types of architectures corresponding to two different morphologies were synthesized: star-shaped morphologies were obtained from rather short backbones, and relatively long grafts, on the one hand, and semiflexible cylinders were grown from rather long backbones and short grafts. These various structures were characterized by nuclear magnetic resonance (NMR) and gel permeation chromatography/light scattering (GPC/LS), and their morphologies were further investigated by atomic force microscopy (AFM). The reported synthetic method provides a robust way to synthesize well-defined polycarbonates with either star-type or brush-type morphologies and graft copolymers made of polyacrylate backbones and polycarbonate grafts. Thermal and mechanical properties of these graft copolymers were also investigated.

Bis(phenolate)-functionalized N-heterocyclic carbene complexes of oxo- and imido-vanadium(V)

Oxo- and imido-vanadium(V) metal complexes supported by bis(phenolate)-functionalized N-heterocyclic carbene (NHC) ligands were synthesized and structurally identified. In the presence of [(Ph3P)2N]Cl ([PPN]Cl), saturated NHC oxo-vanadium complexes showed activity in the coupling of CO2 and cyclohexene oxide (CHO) into cis-cyclohexene carbonate (cis-CHC). More importantly, the oxo-vanadium complex bearing the less electron-donating benzannulated NHC ligand was found to be more active in CHO conversion to poly(cyclohexene carbonate) (PCHC) in addition to the cis-CHC, highlighting the beneficial effect of the weak electron-donating ability of the latter vs. saturated NHC ligands within such vanadium catalysts. Evaluation of the saturated NHC imido-vanadium catalyst performance led to the same activity and selectivity as the analogous oxo-vanadium catalysts owing to its reactivity with CO2 via a [2 + 2] cycloaddition reaction forming an oxo-vanadium species.

Fast-scan chip-calorimetry measurement on crystallization and enthalpy relaxation kinetics of isotactic poly(cyclohexene carbonate)

Isotactic poly(cyclohexene carbonate) (iPCHC) is a newly developed degradable semi-crystalline polymer. In this paper, the crystallization kinetics of iPCHC above the glass transition temperature (Tg) and the enthalpy relaxation kinetics below Tg were studied by using a commercial fast-scan chip-calorimeter—Flash DSC 1. Results showed that half crystallization time of iPCHC as a function of crystallization temperature presented the typical bell shape. And iPCHC showed a maximum crystallization rate at 190 °C, with the half crystallization time 153 s. IPCHC enthalpy relaxation time in 85 °C ~ 100 °C temperature range decreases with isothermal temperature. The above results have great significance to the development of processing and application of novel crystallizable polycarbonate materials.

Configurational Statistics of Poly(cyclohexene carbonate)

Conformational characteristics of poly(cyclohexene carbonate) (PCHC) have been investigated via molecular orbital (MO) calculations and NMR experiments on model compounds. The MO energies establish...

Efficient Production of Poly(Cyclohexene Carbonate) via ROCOP of Cyclohexene Oxide and CO2 Mediated by NNO-Scorpionate Zinc Complexes.

New mono- and dinuclear chiral alkoxide/thioalkoxide NNO-scorpinate zinc complexes were easily synthesized in very high yields, and characterized by spectroscopic methods. X-ray diffraction analysis unambiguously confirmed the different nuclearity of the new complexes as well as the variety of coordination modes of the scorpionate ligands. Scorpionate zinc complexes 2, 4 and 6 were assessed as catalysts for polycarbonate production from epoxide and carbon dioxide with no need for a co-catalyst or activator under mild conditions. Interestingly, at 70 °C, 10 bar of CO2 pressure and 1 mol % of loading, the dinuclear thioaryloxide [Zn(bpzaepe)2{Zn(SAr)2}] (4) behaves as an efficient and selective one-component initiator for the synthesis of poly(cyclohexene carbonate) via ring-opening copolymerization of cyclohexene oxide (CHO) and CO2, affording polycarbonate materials with narrow dispersity values.

(Pyrazolylethyl-amine)zinc(II) carboxylate complexes as catalysts for the copolymerization of CO2 and cyclohexene oxide

Pyrazolyl compounds 2-(3,5-di-tert-butyl-1H-pyrazol-1-yl)ethyl-amine) (L1), 2-(3,5-diphenyl-1H-pyrazol-1-yl)ethyl-amine (L2), and 2-(3-phenyl-5-(trifluoromethyl)-1H-pyrazol-1-yl)ethyl-amine (L3) were reacted with a mixture of zinc(II) acetate and 3,5-dinitrobenzoic acid to form the bidentate complexes [(2-(3,5-di-tert-butyl-1H-pyrazol-1-yl)-ethyl-amine)-Zn(C6H5COO(NO2)2] (1), [(2-(3,5-diphenyl-1H-pyrazol-1-yl)ethyl-amine)Zn(C6H5COO(NO2)2] (2), and [(2-(5-phenyl-3-(trifluoro-methyl)-1H-pyrazol-1-yl)ethyl-amine)Zn(C6H5COO(NO2)2] (3) respectively. All three zinc complexes were tested as catalysts for the copolymerization of CO2 and cyclohexene oxide (CHO) and found active to form poly(cyclohexene carbonate) (PCHC) and cyclohexene carbonate (CCHC) at CO2 pressures as low as 1.5 MPa and under solvent-free conditions in the absence of a co-catalyst. Increase in CO2 pressure resulted in activity and showed selectivity up to 99% selectivity for the formation of the copolymer PCHC. Optimum temperature for the polymerization was 100 °C and even at this temperature selectivity towards formation of PCHC was found to be 99%. The copolymers obtained have moderate molecular weights (3860–11,500 g/mol) and polydispersity indices varying from 2.73 to 4.93.

Iron-catalyzed reactions of CO2 and epoxides to yield cyclic and polycarbonates

The catalytic coupling and polymerization of CO2 and epoxides has been studied for over 50 years. While traditionally dominated by catalytic systems containing cobalt, chromium, and zinc, the use of iron catalysts has emerged in the past 10 years. This review provides an overview of the homogeneous iron-catalyzed transformations of carbon dioxide and epoxides to yield cyclic and/or polycarbonates. It is important to note the potential for cyclic carbonates to be used as monomers for polymer formation via transesterification or by ring-opening polymerization in some cases, e.g., cyclohexene carbonate. Typical catalytic systems are composed of a Lewis acidic iron center and an anionic nucleophilic source, either through an anionic group weakly bound to the metal center or the addition of an external cocatalyst, cooperatively described as a binary catalytic system. This review is divided into two sections: (1) iron catalysts for cyclic carbonates and (2) iron catalysts for polycarbonates. At the end of each section, a table summarizes each catalytic system and the reaction conditions utilized in an attempt to provide a clearer comparison across the literature. Focus is given to highlighting differences in product selectivity, reaction conditions, and relative amounts of cocatalyst used. The use of iron catalysts in CO2/epoxide chemistry has been less explored compared with zinc, cobalt, and chromium catalysts. This review highlights recent examples including iron complexes that deoxygenate epoxides in situ and geometry-dependent selectivity towards either polycarbonate or cyclic carbonate production. Reaction conditions (temperature, CO2 pressure, and amount of nucleophilic cocatalyst) and catalyst structure are all critical in accessing efficient catalysis for polycarbonate formation.

Aliphatic polycarbonates derived from epoxides and CO2: A comparative study of poly(cyclohexene carbonate) and poly(limonene carbonate)

The ring-opening copolymerization (ROCOP) of epoxides and CO2 provides an alternative approach towards polycarbonates and due to their aliphatic nature, they represent an interesting alternative to bisphenol-A based polycarbonates. A Lewis acidic β-diiminate (BDI)CF3-Zn-(SiMe3)2 complex 1 is used in the ROCOP of CO2 with cyclohexene oxide (CHO) and limonene oxide (LO), respectively. The knowledge gained from polymerizations monitored via in situ IR spectroscopy was used to upscale the reactions to a 1 L reactor. The two products poly(cyclohexene carbonate) (PCHC) and poly(limonene carbonate) (PLC) were then characterized via thermal analysis, a multiaxial pressure test, and dynamic mechanical analysis and compared with commercial polymers. While PCHC and PLC were both thermally stable at 150 °C for 20 min and only minor decomposition occurred at 180 °C, PLC is prone to cross-linking at elevated temperatures. This could be prevented by hydrogenation of the double bond or by the addition of an antioxidant. In the mechanical performance, the aliphatic polymers ranged between the highly impact resistant Durabio® and the brittle PMMA but broke without a splintering of the material. Overall, this study enabled a classification of CO2-based polycarbonates, especially of the novel PLC. Additionally, complex 1 was active in the terpolymerization of CHO, LO, and CO2. The formation of an actual terpolymer was confirmed via aliquot gel-permeation chromatography and diffusion-ordered NMR spectroscopy. High-pressure NMR techniques reveal an interesting kinetic feature. CHO gets copolymerized with CO2 exclusively, and LO incorporation only starts when CHO is fully consumed.

Modeling the Mechanism of CO2/Cyclohexene Oxide Copolymerization Catalyzed by Chiral Zinc β-Diiminates: Factors Affecting Reactivity and Isotacticity

Copolymerization of CO2 and cyclohexene oxide (CHO) upcycles CO2 into the value-added, chemically recyclable, thermoplastic poly(cyclohexene carbonate) (PCHC). Using density functional theory, the ...

All-Polycarbonate Thermoplastic Elastomers Based on Triblock Copolymers Derived from Triethylborane-Mediated Sequential Copolymerization of CO2 with Various Epoxides.

Various oxirane monomers including alkyl ether or allyl-substituted ones such as 1-butene oxide, 1-hexene oxide, 1-octene oxide, butyl glycidyl ether, allyl glycidyl ether, and 2-ethylhexyl glycidyl ether were anionically copolymerized with CO2 into polycarbonates using onium salts as initiator in the presence of triethylborane. All copolymerizations exhibited a “living” character, and the monomer consumption was monitored by in situ Fourier-transform infrared spectroscopy. The various polycarbonate samples obtained were characterized by 1H NMR, GPC, and differential scanning calorimetry. In a second step, all-polycarbonate triblock copolymers demonstrating elastomeric behavior were obtained in one pot by sequential copolymerization of CO2 with two different epoxides, using a difunctional initiator. 1-Octene oxide was first copolymerized with CO2 to form the central soft poly(octene carbonate) block which was flanked by two external rigid poly(cyclohexene carbonate) blocks obtained through subsequent copolymerization of cyclohexene oxide with CO2. Upon varying the ratio of 1-octene oxide to cyclohexene oxide and their respective ratios to the initiator, three all-polycarbonate triblock samples were prepared with molar masses of about 350 kg/mol and 22, 26, and 29 mol % hard block content, respectively. The resulting triblock copolymers were analyzed using 1H NMR, GPC, thermogravimetric analysis, differential scanning calorimetry, and atomic force microscopy. All three samples demonstrated typical elastomeric behavior characterized by a high elongation at break and ultimate tensile strength in the same range as those of other natural and synthetic rubbers, in particular those used in applications such as tissue engineering.

Bimetallic Zinc Catalysts for Ring-Opening Copolymerization Processes.

Novel bimetallic zinc acetate complexes supported by heteroscorpionate ligands have been developed for the ring-opening copolymerization of cyclohexene oxide and CO2 and the terpolymerization of cyclohexene oxide, phthalic anhydride, and CO2. Heteroscorpionate ligands precursors L1-L3 were reacted with two equivalents of zinc acetate to afford the dinuclear zinc complexes [{Zn(κ3-bpzappe)}(μ-O2CCH3)3-{Zn(HO2CCH3)}] (1), [{Zn(κ3-bpzbdmape)}(μ-O2CCH3)3-{Zn(HO2CCH3)}] (2), and [{Zn(κ3-bpzbdeape)}(μ-O2CCH3)3{Zn(HO2CCH3)}] (3) in excellent yields. The molecular structure of these compounds was determined spectroscopically and confirmed by X-ray diffraction analysis. Zinc acetate complexes 1-3 were screened as catalysts for the copolymerization of cyclohexene oxide and CO2 to produce poly(cyclohexene)carbonate, and complex 3 was found to be the most active catalyst for this process in the absence of a cocatalyst. Furthermore, the terpolymerization of cyclohexene oxide, phthalic anhydride, and CO2 was studied using the combination of complex 3 and 4-dimethylaminopyridine as catalyst system yielding the corresponding polyester-polycarbonate materials.

A Novel [OSSO]-Type Chromium(III) Complex as a Versatile Catalyst for Copolymerization of Carbon Dioxide with Epoxides.

A new chromium(III) complex, bearing a bis-thioether-diphenolate [OSSO]-type ligand, was found to be an efficient catalyst in the copolymerization of CO2 and epoxides to achieve poly(propylene carbonate), poly(cyclohexene carbonate), poly(hexene carbonate) and poly(styrene carbonate), as well as poly(propylene carbonate)(cyclohexene carbonate) and poly(propylene carbonate)(hexene carbonate) terpolymers.

Heteronuclear, Monomer-Selective Zn/Y Catalyst Combines Copolymerization of Epoxides and CO2 with Group-Transfer Polymerization of Michael-Type Monomers.

Terpolymerizations of cyclohexene oxide (CHO), CO2, and the Michael-type monomer 2-vinylpyridine (2VP) are presented. The combination of two distinct polymerization mechanisms was enabled by the synthesis of a heterobifunctional complex (3). Its β-diiminate zinc moiety allows the ring-opening copolymerization of CHO and CO2, whereas the yttrium metallocene catalyzed the rare earth metal-mediated group-transfer polymerization of the polar vinyl monomer. Both units were connected via the CH-bond activation of a pyridyl-alkoxide linker. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF-MS) revealed the successful transfer of the linker to the end-group of the respective homopolymers poly(cyclohexene carbonate) (PCHC) and poly(2VP) (P2VP) being the prerequisite for copolymer formation. Aliquot gel-permeation chromatography (GPC) analysis and solubility behavior tests confirmed the P2VP-block(b)-PCHC terpolymer formation via two pathways, a sequential and a one-pot procedure. Furthermore, the versatility of the method was demonstrated by introducing 2-isopropenyl-2-oxazoline (IPOx) as the second Michael-type monomer that yielded the terpolymer poly(IPOx)-b-PCHC.

Research Progress of Biodegradable Polyester Polyols Based on Ring-Opening Polymerization of Cyclohexene Carbonate

The polycarbonate polyols(PCD) obtained by ring-opening polymerization of a general cyclic monomer is mostly a linear flexible structure, which is used as a raw material to synthesize polyurethanes, and it is difficult to simultaneously ensure good thermal-mechanical properties and weather resistance due to insufficient rigidity of the main chain. However, PCD based on ring-opening polymerization of cyclohexene carbonate (CHC), endowing with polyurethanes good mechanical properties, weather ability and biological stability because of the rigid structure of six-membered aliphatic rings in the main chain. Therefore, in this paper, the method and principle of preparing new polycarbonate polyols based on ring-opening polymerization of cyclohexene carbonate (CHC) are introduced. And the problems and countermeasures in its development and its application in polyurethane materials are discussed.

Switchable Catalysis Improves the Properties of CO2-Derived Polymers: Poly(cyclohexene carbonate-b-ε-decalactone-b-cyclohexene carbonate) Adhesives, Elastomers, and Toughened Plastics.

Carbon dioxide/epoxide copolymerization is an efficient way to add value to waste CO2 and to reduce pollution in polymer manufacturing. Using this process to make low molar mass polycarbonate polyols is a commercially relevant route to new thermosets and polyurethanes. In contrast, high molar mass polycarbonates, produced from CO2, generally under-deliver in terms of properties, and one of the most widely investigated, poly(cyclohexene carbonate), is limited by its low elongation at break and high brittleness. Here, a new catalytic polymerization process is reported that selectively and efficiently yields degradable ABA-block polymers, incorporating 6–23 wt % CO2. The polymers are synthesized using a new, highly active organometallic heterodinuclear Zn(II)/Mg(II) catalyst applied in a one-pot procedure together with biobased ε-decalactone, cyclohexene oxide, and carbon dioxide to make a series of poly(cyclohexene carbonate-b-decalactone-b-cyclohexene carbonate) [PCHC-PDL-PCHC]. The process is highly selective (CO2 selectivity >99% of theoretical value), allows for high monomer conversions (>90%), and yields polymers with predictable compositions, molar mass (from 38–71 kg mol–1), and forms dihydroxyl telechelic chains. These new materials improve upon the properties of poly(cyclohexene carbonate) and, specifically, they show good thermal stability (Td,5 ∼ 280 °C), high toughness (112 MJ m–3), and very high elongation at break (>900%). Materials properties are improved by precisely controlling both the quantity and location of carbon dioxide in the polymer chain. Preliminary studies show that polymers are stable in aqueous environments at room temperature over months, but they are rapidly degraded upon gentle heating in an acidic environment (60 °C, toluene, p-toluene sulfonic acid). The process is likely generally applicable to many other lactones, lactides, anhydrides, epoxides, and heterocumulenes and sets the scene for a host of new applications for CO2-derived polymers.

Synthesis, structures, and thermal properties of terpolymers of propylene oxide, carbon dioxide, and cyclohexene oxide

High molecular weight block terpolymers with different contents of polypropylene carbonate and cyclohexene carbonate units in the polymer chain were synthesized by the copolymerization of carbon dioxide, propylene oxide, and cyclohexene oxide. Zinc adipate was used as a catalyst. The terpolymerization products were characterized by 1H and 13C NMR spectroscopy, IR spectroscopy, GPC, DSC, and DMA methods. The influence of the reaction conditions on the composition, microstructure, and molecular-weight and thermal characteristics was studied.

Rapid Chemical Reaction Monitoring by Digital Microfluidics-NMR: Proof of Principle Towards an Automated Synthetic Discovery Platform.

Microcoil nuclear magnetic resonance (NMR) has been interfaced with digital microfluidics (DMF) and is applied to monitor organic reactions in organic solvents as a proof of concept. DMF permits droplets to be moved and mixed inside the NMR spectrometer to initiate reactions while using sub-microliter volumes of reagent, opening up the potential to follow the reactions of scarce or expensive reagents. By setting up the spectrometer shims on a reagent droplet, data acquisition can be started immediately upon droplet mixing and is only limited by the rate at which NMR data can be collected, allowing the monitoring of fast reactions. Here we report a cyclohexene carbonate hydrolysis in dimethylformamide and a Knoevenagel condensation in methanol/water. This is to our knowledge the first time rapid organic reactions in organic solvents have been monitored by high field DMF-NMR. The study represents a key first step towards larger DMF-NMR arrays that could in future serve as discovery platforms, where computer controlled DMF automates mixing/titration of chemical libraries and NMR is used to study the structures formed and kinetics in real time.

Rapid Chemical Reaction Monitoring by Digital Microfluidics‐NMR: Proof of Principle Towards an Automated Synthetic Discovery Platform

AbstractMicrocoil nuclear magnetic resonance (NMR) has been interfaced with digital microfluidics (DMF) and is applied to monitor organic reactions in organic solvents as a proof of concept. DMF permits droplets to be moved and mixed inside the NMR spectrometer to initiate reactions while using sub‐microliter volumes of reagent, opening up the potential to follow the reactions of scarce or expensive reagents. By setting up the spectrometer shims on a reagent droplet, data acquisition can be started immediately upon droplet mixing and is only limited by the rate at which NMR data can be collected, allowing the monitoring of fast reactions. Here we report a cyclohexene carbonate hydrolysis in dimethylformamide and a Knoevenagel condensation in methanol/water. This is to our knowledge the first time rapid organic reactions in organic solvents have been monitored by high field DMF‐NMR. The study represents a key first step towards larger DMF‐NMR arrays that could in future serve as discovery platforms, where computer controlled DMF automates mixing/titration of chemical libraries and NMR is used to study the structures formed and kinetics in real time.

Mechanism investigation of thermal degradation of CO2-based poly(cyclohexene carbonate caprolactone)

The thermal degradation behaviors and mechanisms of CO2-based poly(cyclohexene carbonate caprolactone)s (PCHCCLs) were deeply studied taking advantage of thermogravimetric analysis/Fourier transform infrared spectrometry (TG/FTIR) and pyrolysis gas chromatography/mass spectrometry (Py-GC/MS) techniques. The experimental results indicate that the decomposition temperatures of PCHCCLs increase with the increasing contents of polycaprolactone (PCL) segments. Backbiting reaction was found to be the dominant degradation pathway for PCHCCLs, and a complicated random rupture process was also observed at higher pyrolysis temperature.

Nickel-catalyzed copolymerization of carbon dioxide with internal epoxides by di-nuclear bis(benzotriazole iminophenolate) complexes

We report the synthesis of structurally well-characterized di-nuclear nickel bis(benzotriazole iminophenolate) (BiIBTP) complexes containing diverse mono- or bi-dentate monoanionic coligands for the utilization of copolymerization of carbon dioxide (CO2) with internal epoxides. The molecular structures of complexes 1–3 can be ascribed to bimetallic nickel(II) species containing a hexadentate BiIBTP main ligand and two homo-coligands of pentafluorobenzoate, pentafluorophenolate or chloride, whereas 4 and 5 are BiIBTP-ligated di-nickel chloride analogues mixed with carboxylate coligands. Di-nickel complexes 1 and 3 supported by O2CC6F5 and Cl coligands were demonstrated to be efficient catalysts for alternating copolymerization of CO2 with cyclohexene oxide (CHO) to afford CO2-based poly(cyclohexene carbonate)s (PCHCs) with >99% carbonate repeated units. Particularly, di-Ni di-chloride complex 3 was capable of giving high activity with a turnover frequency of 688 h−1 for such copolymerization under the optimal conditions. Interestingly, di-Ni catalyst 1 enables us to produce the low molecular weight di-hydroxyl end-capped PCHCs with unimodal molecular weight distributions while commercially available CHO without further purification was used as the epoxide monomer. In addition to CO2-CHO copolymerization, bimetallic complex 1 was also found to effectively copolymerize CO2 with cyclopentene oxide, generating highly alternating poly(cyclopentene carbonate)s with molecular weights in a broad range. Kinetic studies of CO2/CHO copolymerization catalyzed by 1 were investigated using 1H NMR spectroscopy and revealed the first-order dependence for both catalyst 1 and CHO concentrations.