Six-membered Cyclic Carbonate Research Articles

Ring-opening polymerization of six-membered cyclic carbonates initiated by ethanol amine derivatives and their application to protonated or quaternary ammonium salt-functionalized polycarbonate films

Ring-opening polymerization (ROP) of monofunctional neopentylglycol carbonate (NPGC) with or without bifunctional di(trimethylolpropane) carbonate (DTMPC), which are derived from available corresponding alcohols, affords linear polycarbonates or covalently-linked polycarbonate networks, respectively. A series of available ethanol amine derivatives having the different numbers of 2-hydroxylethyl arms (N,N,N’,N’-tetrakis(2-hydroxyethyl)ethylenediamine, triethanolamine, N-methyldiethanolamine or N,N-dimethylethanolamine) initiates the ROP of NPGC to afford star-shaped, telechelic, or linear polycarbonates bearing tertiary amines with well-controlled molecular weights and relatively narrow polydispersities Furthermore, the copolymerization of NPGC and DTMPC in the presence of these initiators readily gives tertiary amine-modified polycarbonate films with well transparency and flexibility. These amino groups are easily converted to ammonium salts by protonation with acids, while the quaternization with benzyl bromide is strongly affected by the steric hindrance of these amines. N-Methyldiethanolamine or N,N-dimethylethanolamine residues in these films react easily with benzyl bromide to give quaternary ammonium salt-functionalized films. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016, 54, 487–497

Highly Chemoselective Catalytic Coupling of Substituted Oxetanes and Carbon Dioxide.

The chemoselective coupling of oxetanes and carbon dioxide to afford functional, heterocyclic organic compounds known as six-membered cyclic carbonates remains a challenging topic. Here, an effective method for their synthesis relying on the use of Al catalysis is described. The catalytic reactions can be carried out with excellent selectivity for the cyclic carbonate product tolerating various (functional) groups present in the 2- and 3-position(s) of the oxetane ring. The presented methodology is the first general approach towards the formation of six-membered cyclic carbonates (6MCCs) through oxetane/CO2 coupling chemistry. Apart from a series of substituted six-membered cyclic carbonates, also the unprecedented room-temperature coupling of oxetanes and CO2 is disclosed giving, depending on the structural features of the substrate, a variety of five- and six-membered heterocyclic products. A mechanistic rationale is presented for their formation and support for the intermediary presence of a carbonic acid derivative is given. The presented functional carbonates may hold great promise as building blocks in organic synthesis and the development of new, biodegradable polymers.

Macromolecular Design via an Organocatalytic, Monomer-Specific and Temperature-Dependent "On/Off Switch". High Precision Synthesis of Polyester/Polycarbonate Multiblock Copolymers.

The employment of a monomer-specific “on/off switch” was used to synthesize a nine-block copolymer with a predetermined molecular weight and narrow distribution (Đ = 1.26) in only 2.5 h. The monomers consisted of a six-membered cyclic carbonate (i.e., 2-allyloxymethyl-2-ethyl-trimethylene carbonate (AOMEC)) and ε-caprolactone (εCL), which were catalyzed by 1,5,7-triazabicyclo[4.4.0]-dec-5-ene (TBD). The dependence of polymerization rate with temperature was different for the two monomers. Under similar reaction conditions, the ratio of the apparent rate constant of AOMEC and εCL [kpapp(AOMEC)/kpapp(εCL)] changes from 400 at T = −40 °C to 50 at T = 30 °C and 10 at T = 100 °C. Therefore, by decreasing the copolymerization temperature from 30 °C to −40 °C, the conversion of εCL can be switched “off”, and by increasing the temperature to 30 °C, the conversion of εCL can be switched “on” again. The addition of AOMEC at T = −40 °C results in the formation of a pure carbonate block. The cyclic addition of AOMEC to a solution of εCL along with a simultaneous temperature change leads to the formation of multiblock copolymers. This result provides a new straightforward synthetic route to degradable multiblock copolymers, yielding new interesting materials with endless structural possibilities.

Synthesis of high molecular flexibility polycarbonates for solid polymer electrolytes

A new self-plasticizing aliphatic polycarbonate comprising flexible alkyl and alkyl ether side groups was designed and synthesized from six-membered cyclic carbonate monomers with the aim of producing a material with high molecular flexibility (low Tg) and concomitant high ionic conductivity when used as a polymer electrolyte. The Tg of the novel polycarbonate was determined to be −49.4°C at a molecular weight of 34 400gmol−1, which is the lowest reported Tg to date for a substituted poly(trimethylene carbonate). UV-crosslinked polymer electrolytes were produced based on this novel material together with LiTFSI salt and showed ionic conductivities in the range of 2×10−8 to 2×10−7Scm−1 at room temperature and 1×10−6 to 1×10−5Scm−1 at 100°C. The limited ionic conductivities of these electrolytes indicate that high molecular flexibility alone does not guarantee fast ion transport in solid polymer electrolytes and that other factors, such as the polarity of the polymer host material, will also influence the transport properties of the electrolyte.

Ring-Closing Depolymerization: A Powerful Tool for Synthesizing the Allyloxy-Functionalized Six-Membered Aliphatic Carbonate Monomer 2-Allyloxymethyl-2-ethyltrimethylene Carbonate

Ring-closing depolymerization is demonstrated to be a powerful synthetic methodology for the formation of six-membered functional aliphatic carbonate monomers, providing a rapid, straightforward, inexpensive, and green route for obtaining six-membered functional aliphatic carbonate monomers at a scale greater than 100 g. The utility of this technique was observed via the synthesis of the allyloxy-functionalized six-membered cyclic carbonate monomer 2-allyloxymethyl-2-ethyltrimethylene carbonate (AOMEC). The synthesis was performed in a one-pot bulk reaction, starting from trimethylolpropane allyl ether, diethyl carbonate, and NaH, resulting in a final AOMEC yield of 63%. The synthetic methodology is based upon the reversible nature of this class of polymers. The anionic environment produced by NaH was observed to be sufficient to mediate the monomer equilibrium concentration; thus, an additional catalyst is not required to induce depolymerization. 1,5,7-Triazabicyclo[4.4.0]dec-5-ene (TBD) was demonstrated to be a very active catalyst for the ring-opening polymerization (ROP) of AOMEC, resulting in a rapid (kpapp = 28.2 s–1) and controlled polymerization with a low dispersity (Đ = 1.2). The availability and activity of the functionality of poly(AOMEC)s were established through subsequent postpolymerization functionalization via the UV-initiated thiol–ene chemistry of poly(AOMEC) with 1-dodecanethiol and benzophenone as a radical initiator. The functionalization proceeded with high control and with a linear relation between the molecular weight and conversion of the unsaturation, revealing the high orthogonality of the reaction and the stability of the carbonate backbone. Hence, as a synthetic methodology, depolymerization provides a straightforward and simple approach for the synthesis of the highly versatile functional carbonate AOMEC. In addition, formation of the monomer does not require any solvents, reactive ring-closing reagents, or transition-metal-based depolymerization catalysts, thereby providing a “greener” route for obtaining functional carbonate monomers and polymers.

Synthesis and hydrolytic degradation of aliphatic polycarbonate based on dihydroxyacetone

The six-membered cyclic carbonate monomer, 2,2-dimethoxy-1,3-propanediol carbonate based on dihydroxyacetone with methanol ketal protected carbonyl group, was prepared by a two-step reaction including protection and ring-closing, starting from dihydroxyacetone. The ring-opening polymerization of 2,2-dimethoxy-1,3-propanediol carbonate was carried out in bulk at 110–140°C initiated by stannous octanoate to give polycarbonate, poly(2,2-dimethoxypropane-1,3-diol carbonate). The effects of different reaction conditions including different catalyst, reaction temperature, molar ratio of monomer to initiator and polymerization time on the polymerization were investigated. Polycarbonate was obtained with the yield of 58.9–91.0%. The number average molecular weight of polycarbonate was in the range of 1.43 × 104 to 13.82 × 104 with polydispersity indexes from 1.31 to 1.91. The protecting ketal group was partly removed by hydrolysis using 50% trifluroacetic acid as a catalyst to give a functional polycarbonate containing 70% ketone carbonyl group, which improved the hydrophilicity of initial polycarbonate. The in vitro degradation tests were carried out in a phosphate buffer solution with pH 7.4 at 37°C, which showed that the modified polycarbonate degraded completely after 5 days.

Catalytic Asymmetric Ring-Opening of σ-Symmetric Cyclic Carbonates with Chiral Brønsted Acid Catalysts

Enantioselective ring-opening of σ-symmetric six-membered cyclic carbonates with benzyl alcohol catalyzed by BINOL-based chiral phosphoric acids was achieved in up to 81% enantiomeric excess at 5 mol% catalyst loading.

Synthesis and post-polymerisation modifications of aliphatic poly(carbonate)s prepared by ring-opening polymerisation

Owing to their low toxicity, biocompatibility and biodegradability, aliphatic poly(carbonate)s have been widely studied as materials for biomedical application. Furthermore, the synthetic versatility of the six-membered cyclic carbonates for the realization of functional degradable polymers by ring-opening polymerisation has driven wider interest in this area. In this review, the synthesis and ring-opening polymerisation of functional cyclic carbonates that have been reported in the literature in the past decade are discussed. Finally, the post-polymerisation modification methods that have been applied to the resulting homopolymers and copolymers and the application of the materials are also discussed.

2-Amino-1,3-propane diols: a versatile platform for the synthesis of aliphatic cyclic carbonate monomers

Starting from commercially available 2-amino-1,3-propane diols, a variety of functional cyclic carbonate monomers were synthesized through a general two-step strategy. First the amino group was chemo-selectively reacted with a diverse set of electrophiles to result in functional diol intermediates (1), which were then cyclized in an intramolecular fashion to generate a series of functional aliphatic six-membered cyclic carbonate monomers (2). The unique feature of this approach is its ability to install concurrently two different functional groups. This includes a specific tethered functional group and a second functional group, which are installed in the monomer-forming reactions. Selected monomers were subjected to organo-catalytic ring opening polymerization to produce well-defined homopolymers and copolymers (ĐM ≥ 1.5) with controlled composition. Primary amine containing polymers were also readily accessed via post-polymerization acidolysis of a tBoc-derived monomer (2k). This approach will provide direct access to functional biodegradable polymers and impact the development of next-generation materials for biomedical and environmentally friendly products.

Optimization of a two‐step process comprising lipase catalysis and thermal cyclization improves the efficiency of synthesis of six‐membered cyclic carbonate from trimethylolpropane and dimethylcarbonate

Six-membered cyclic carbonates are potential monomers for phosgene and/or isocyanate free polycarbonates and polyurethanes via ring-opening polymerization. A two-step process for their synthesis comprising lipase-catalyzed transesterification of a polyol, trimethylolpropane (TMP) with dimethylcarbonate (DMC) in a solvent-free system followed by thermal cyclization was optimized to improve process efficiency and selectivity. Using full factorial designed experiments and partial least squares (PLS) modeling for the reaction catalyzed by Novozym®435 (N435; immobilized Candida antarctica lipase B), the optimum conditions for obtaining either high proportion of monocarbonated TMP and TMP-cyclic-carbonate (3 and 4), or dicarbonated TMP and monocarbonated TMP-cyclic-carbonate (5 and 6) were found. The PLS model predicted that the reactions using 15%-20% (w/w) N435 at DMC:TMP molar ratio of 10-30 can reach about 65% total yield of 3 and 4 within 10 h, and 65%-70% total yield of 5 and 6 within 32-37 h, respectively. High consistency between the predicted results and empirical data was shown with 66.1% yield of 3 and 4 at 7 h and 67.4% yield of 5 and 6 at 35 h, using 18% (w/w) biocatalyst and DMC:TMP molar ratio of 20. Thermal cyclization of the product from 7 h reaction, at 110°C in the presence of acetonitrile increased the overall yield of cyclic carbonate 4 from about 2% to more than 75% within 24 h. N435 was reused for five consecutive batches, 10 h each, to give 3+4 with a yield of about 65% in each run.

Non-isocyanate polyurethanes: from chemistry to applications

Conventional polyurethanes involve the use of isocyanates, which require hazardous and toxic phosgene for their manufacture. These monomers cannot be manufactured without elaborate safety devices and huge investment. Isocyanates are also considerably toxic and moisture sensitive. Growing global awareness of the need to protect our environment and continually strive to ensure the safety, health and well-being of those in the industry and consumers has created a demand for environment-friendly products. The cyclic carbonate–primary amine addition reaction which results in hydroxyurethanes is a unique reaction and has been extensively studied over the last few years. This chemistry is now attracting research interest due to its potential application in the preparation of “green”, non-porous, moisture-insensitive, isocyanate free polyurethanes. This review focuses on catalysis, the mechanism involved in the formation of Non-Isocyanate Polyurethanes (NIPU) from five-membered cyclic carbonates and the reaction kinetics for their synthesis. The higher homologues of the cyclic carbonate family, the six-membered cyclic carbonates, are similar to, but more reactive than, the five-membered cyclic carbonates and can also serve as a source for production of isocyanate free polyurethanes. This review also summarizes various application of NIPU in coatings, composites, construction and biochemical fields.

Semicrystalline Dihydroxyacetone Copolymers Derived from Glycerol

The ring-opening polymerization of glycerol-derived six-membered cyclic dimethylacetal dihydroxyacetone carbonate (MeO2DHAC) have been studied both in solution and bulk conditions with organic catalysts. The guanidine 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) was the most active catalyst in solution, whereas the thiourea/sparteine catalytic system displayed the most predictable kinetics. Ring-opening polymerization of MeO2DHAC or copolymerization with ε-caprolactone (CL) in the melt occurred readily with TBD as catalyst to afford random copolymers. Acetal deprotection afforded the polycarbonate poly(dihydroxyactone carbonate) (p(DHAC)) or poly(carbonate ester) copolymers p(DHAC-r-CL). The polycarbonate p(DHAC) is a high-melting thermoplastic with a melting point of 246 °C. The p(DHAC-r-CL) copolymers all displayed semicrystalline behavior as evidenced by DSC and WAXS analysis with Tg and Tm changing as a function of comonomer composition. These new materials could have potential use in biomedical applications or as biomass-derived thermoplastics.

Alkyloxycarbonyl group migration in furanosides

A migration of methyloxycarbonyl group from secondary to primary hydroxyl was observed in furanosides (ribosides and xylosides) under usual desilylation conditions using tetrabutylammonium fluoride. The migration was studied further on several alkyloxycarbonyl furanosides under either basic or acidic conditions. As follows from 13C labelling experiments and product distribution, the migration in xylosides, proceeds intramolecularly via six-membered cyclic carbonate, whereas in ribosides, the migration is intermolecular. Acidic conditions prevented the migration in ribosides whereas the migration in xylosides was circumvented under neutral conditions.

Reduction-sensitive core-cross-linked mPEG–poly(ester-carbonate) micelles for glutathione-triggered intracellular drug release

A functionalized six-membered cyclic carbonate monomer containing a protected thiol group, 2-(2,4-dinitrophenylthio)ethyl-5-methyl-2-oxo-1,3-dioxane-5-carboxylate (MTC), was prepared. Ring-opening polymerization (ROP) of MTC and L-lactide (LA) initiated by monohydroxyl poly(ethylene glycol) (mPEG) was successfully performed with controlled polymer molecular weight and molecular weight distribution. The structures of the obtained monomer and copolymers were confirmed by NMR and FTIR. After deprotection under mild conditions, the amphiphilic block copolymer was self-assembled into micelles in aqueous solution. By oxidation of the free thiol groups in the PMTC segments, the micelles with the cross-linked core were formed, and the enhanced stability against disruptive conditions was demonstrated by dynamic light scattering (DLS) measurement in the presence of DMF. Doxorubicin (DOX) was loaded into the micelles as a model drug. The in vitro DOX release behaviors indicated that cross-linking of the micelle cores resulted in a slow drug release and this process was greatly accelerated by adding glutathione (GSH) solution with comparable concentrations to intracellular levels in tumor cells. The cross-linked micelles were demonstrated to be efficiently internalized into the cells. Faster intracellular DOX release was observed by confocal laser scanning microscopy (CLSM) in the GSH pretreated MCF-7 cells than in the unpretreated MCF-7 cells. In vitro MTT assay revealed that the cross-linked micelles were biocompatible with L929 cells and MCF-7 cells. As expected, DOX-loaded cross-linked micelles showed higher cellular proliferation inhibition towards glutathione pretreated MCF-7 cells than that towards the unpretreated ones at various GSH concentrations. These results indicated that the bioreducible core-cross-linked micelles can be used as drug carriers for intelligent drug delivery.

Diversity in cyclic carbonates: synthesis of triazole-functional monomers using click chemistry

Triazole-functional cyclic carbonates are presented as a new class of functional monomers for ring-opening polymerisation. Starting from bromo-functional six-membered cyclic carbonates, a series of triazole-functional monomers was synthesised using click chemistry. This synthetic strategy allows for facile synthesis of a great number of structurally diverse monomers from just a few azide-functional precursors.

Synthesis and polymerization of alkyl halide-functional cyclic carbonates

To increase the diversity in functional aliphatic polycarbonates, a series of novel chloro- and bromo-functional six-membered cyclic carbonate monomers were synthesized. Despite asymmetry in the monomer functionalities, homopolymerization of the monomers afforded semicrystalline polycarbonates with a high tendency to crystallize from the melt and/or on precipitation from a THF solution. Melting points were found in the 90–105 °C or 120–155 °C range for polymers comprising methyl or ethyl moieties, respectively, in the backbone. The monomers were further copolymerized with trimethylene carbonate to form random copolymers. Even among some of these random copolymers elements of semicrystallinity were found as confirmed by melting endotherms in DSC. The results clearly show that the incorporation of alkyl halide functionalities in aliphatic polycarbonates may lead to materials with a high ability to form crystallites, even in random copolymers, likely driven by polar interactions due to the presence of the halide functionalities.

Lipase-mediated synthesis of six-membered cyclic carbonates from trimethylolpropane and dialkyl carbonates: Influence of medium engineering on reaction selectivity

Six-membered cyclic carbonates are potential monomers for aliphatic polycarbonates and polyurethanes in a process without using toxic phosgene and isocyanate. Lipase catalyzed transesterification of the polyol, trimethylolpropane (TMP) with dimethyl carbonate (DMC) or diethyl carbonate (DEC) followed by thermal cyclization was used for synthesis of six-membered cyclic carbonates with pendant hydroxyl and alkoxycarbonyloxyl groups. Immobilized lipase B from Candida antarctica (Novozym (R) 435) was used as the catalyst. Mixture of a hydrophilic solvent such as THF for high solubility of TMP, and a hydrophobic solvent such as toluene, were selected as the best solvent system for achieving high substrate conversion and selectivity. A relationship between polyol conversion and solvent hydrophobicity (log P) and solvent type, respectively, was established. THF:toluene system at a ratio of 0.5:1.0 (v/v) provided high degree of TMP conversion to product with high proportion of cyclic carbonates (>80%). The cyclic carbonate with pendant hydroxyl group was obtained with almost 85% selectivity at TMP conversion of 68.6% using 10% (w/w)Novozym (R) 435 at TMP:DMC ratio of 1:1. However, at TMP:DMC ratio of 1:5 and the same biocatalyst concentration, the TMP conversion was 100% with 72% selectivity for the cyclic carbonate with pendant alkoxycarbonyloxyl group. The product formed was without or with less content of linear carbonates, bis and tris(methoxycarbonyloxy)-TMP, as compared to that in a solvent-free system. The reactivity of DEC was lower than that of DMC. The reaction pathway leading to the formation of cyclic carbonate in this process comprised enzymatic carbonation of TMP with alkylcarbonates and thermal cyclization of linear carbonates. The process affords high degree of conversion of polyol to cyclic carbonates and provides a potentially attractive synthetic route for monomers of polycarbonates and polyurethanes. (C) 2011 Elsevier B.V. All rights reserved. (Less)

Aliphatic Polycarbonates Produced from the Coupling of Carbon Dioxide and Oxetanes and Their Depolymerization via Cyclic Carbonate Formation

The (salen)CrCl/onium salt catalyzed coupling reactions of several oxetane derivatives and carbon dioxide are reported. The oxetanes investigated contain substituents in the 3-position covering a range of steric requirements. The oxetanes examined include, 3,3-dimethyloxetane, 3-methoxymethyl-3-methyloxetane, and 3-benzyloxymethyl-3-methyloxetane. The rates of reaction of these oxetanes with CO2 were found to be significantly slower than the corresponding process with the parent oxetane monomer. Furthermore, in these instances the formation of copolymer was found to proceed via the preformed cycloaddition product, i.e., the six-membered cyclic carbonate, to a greater extent and increasing with the steric bulk of the substituents on oxetane. For these sterically more hindered oxetanes, the CO2 coupling reaction carried out in toluene at 110 °C reached an equilibrium product distribution of copolymer to cyclic carbonate which increased in cyclic carbonate product with increasing steric requirements of the oxetane monomer. For example, the catalyzed coupling of the parent oxetane and CO2 provides a copolymer to cyclic carbonate ratio of greater than 95%, whereas the corresponding product distribution for 3-benzyloxymethyl-3-methyloxetane was observed to be 60%. The catalytic rate of depolymerization of a purified sample of the copolymer afforded from 3-benzyloxymethyl-3-methyloxetane and CO2 to the corresponding cyclic carbonate, 5-benzyloxymethyl-5-methyl-1,3-dioxan-2-one, was found to be greatly retarded when carried out in an atmosphere of CO2.

Solvent-free lipase-mediated synthesis of six-membered cyclic carbonates from trimethylolpropane and dialkyl carbonates

Six-membered cyclic carbonates with hydroxyl and/or alkoxycarbonyloxy groups, as potential monomers for polyurethanes and polycarbonates, were prepared by the reaction between trimethylolpropane (TMP) with dimethyl carbonate (DMC) or diethylcarbonate (DEC) mediated by immobilized Candida antarcticalipase B, Novozym® 435 in a solvent-free medium. The dialkyl carbonate served as a solvent for the reaction. The solubility of TMP at 50 °C was 565 mg mL−1 in DMC, and 64.8 mg mL−1 in DEC. Reactions using biocatalyst concentrations of 10, 20 and 40% (w/w of TMP) showed similar profiles, with a linear increase in the conversion of TMP to 90% within 24 h, and complete conversion within 48 h. At biocatalyst concentrations of 2.5 and 5% (w/w of TMP), the main products were mono-carbonated TMP (3) and/or cyclic carbonate (4), while di and tri-carbonated TMP (5, 7) were obtained at lipase concentrations of 20 and 40%. The reactivity of DEC was lower than that of DMC, but led to higher selectivity in production of 3 or 4. A large fraction of the linear carbonates in the product mixture were cyclized by disproportionation involving heating at 60–80 °C without any catalyst. The total yield of cyclic carbonates was about 85% after thermal treatment at 80 °C. This process, consisting of lipase-catalyzed transesterification and thermal disproportionation, provides a novel and more environmentally friendly approach for the synthesis of cyclic carbonates without using toxic organic solvents, phosgene or isocyanate.

Conformational isomerization of polymethyl-substituted six-membered cyclic carbonates

Conformational isomerization of polymethyl-substituted six-membered cyclic carbonates