Six-membered Cyclic Carbonate Research Articles

Reprocessing, shape recovery and dielectric properties of nanocomposites of Polyhydroxyurethane with barium Titanate

Poly(N-vinyl pyrrolidone) (PVPy) chains were grafted onto the surfaces of barium titanate (BaTiO3) nanoparticles via the surface-initiated living/controlled radical polymerization of N-vinyl pyrrolidone. The PVPy-grafted BaTiO3 nanoparticles were then incorporated into a crosslinked polyhydroxyurethane (PHU) which was derived from bis(six-membered) cyclic carbonate and a triamine (i.e., Jeffamine T400). It was found that BaTiO3 nanoparticles were uniformly dispersed into the PHU matrix. The generation of nanocomposites resulted that the glass transition temperatures (Tg’s) and mechanical properties were significantly enhanced. In the meantime, the nanocomposites had the dielectric properties superior to control PHU; the shape memory properties of the materials were significantly improved in terms of response, fixity of transient shape and recovery of the original shapes. Thanks to transcarbamoylation of hydroxyurethane structural units, the crosslinked nanocomposites can be reprocessed at elevated temperature. It was found that dibutyltin dilaurate (DBTDL) was an effective catalyst to decrease the Arrhenius activation energy of the dynamic reaction; the reprocessing of the nanocomposites can be carried out at the temperature as low as 120 °C.

Catalytic Domino Three-Component Synthesis of Functionalized Heterocycles from Carbon Dioxide.

A catalytic domino, three-component reaction has been developed for the transformation of carbon dioxide into functionalized six-membered cyclic carbonates. The catalytic process combines an initial carboxylative cyclization of β-epoxy alcohols followed by an oxa-Michael reaction affording an unparalleled scope of heterocyclic structures. The wide range of functional groups, including free-alcohols, empowers the access to a range of products including C11-oxo-based bicyclic heterocycles. The versatility of these functionalized carbonates is further complemented by a series of synthetic diversifications. Control experiments are consistent with the first step of this domino process being promoted by a binary Lewis acid/base catalyst, while the second stage only requires catalytic base.

Chemically Recyclable Biobased Non-Isocyanate Polyurethane Networks from CO2 -Derived Six-membered Cyclic Carbonates.

Non-isocyanate polyurethanes (NIPUs) are widely studied as sustainability potential, because they can be prepared without using toxic isocyanates in the synthesis process. The aminolysis of cyclic carbonate to form NIPUs is a promising route. In this work, a series of NIPUs is prepared from renewable bis(6-membered cyclic carbonates) (iEbcc) and amines. The resulting NIPUs possess excellent mechanical properties and thermal stability. The NIPUs can be remolded via transcarbamoylation reactions, and iEbcc-TAEA-10 (the molar ratio of tris(2-aminoethyl)amine in amines is 10%) still get a recovery ratio of 90% in tensile stress after three cycles of remolding. In addition, the obtained materials can be chemically degraded into bi(1,3-diol) precursors with high purity (>99%) and yield (>90%) through alcoholysis. Meanwhile, the degraded products can be used to regenerate NIPUs with similar structures and properties as the original samples. The synthetic strategy, isocyanate-free and employing isoeugenol and carbon dioxide (CO2 ) as building blocks, makes this approach an attractive pathway to NIPU networks taking a step toward a circular economy.

Synthesis of Random, Gradient, and Block-like Terpolycarbonates via One-Pot Terpolymerization of Epoxide, CO2, and Six-Membered Cyclic Carbonates

Multi-polymerization is regarded as a valuable strategy to tailor material performances by incorporating well-chosen monomers and tuning monomer sequence distributions in the polymer backbones. Despite that considerable advances have been made in the past decades, the modification of CO2-based polycarbonate materials is still in its infancy. In this contribution, a series of polycarbonate terpolymers with diverse chain structures were fabricated through a dissymmetric Cr complex-catalyzed one-pot terpolymerization of cyclohexene oxide (CHO), CO2 with six-membered cyclic carbonates (6CCs). The reaction conditions (temperature, feeding ratio, and CO2 pressure) as well as the 6CC substituents played a critical role in tailoring the sequence distributions of CHO/CO2/6CC terpolymers from random to gradient or block-like sequences. It was noteworthy that the average lengths of both sequences could be modulated by adjusting the feeding monomer ratios or reaction temperature, as detected by quantitative 13C NMR spectroscopy of purified terpolymers. Besides, DSC revealed that the glass-transition temperature of the obtained terpolymers had a wide range of 69.5–115.5 °C based on the polymer architecture.

Carbonate-Terminated Self-Assembled Monolayers for Mimicking Nanoscale Polycarbonate Surfaces

Two carbonate-terminated alkanethiol molecules having different positional isomers of a six-membered cyclic carbonate group, 3-COC12SH and 2-COC12SH, were synthesized and used to generate self-assembled monolayers (SAMs) on gold to serve as mimics of the surfaces of commercially available poly(propylene carbonate) (PPC) and poly(ethylene carbonate) (PEC). The adsorbate molecules were characterized using 1H and 13C nuclear magnetic resonance spectroscopy and high-resolution mass spectrometry. The corresponding SAMs on gold were characterized by ellipsometry, contact angle goniometry, polarization-modulation infrared reflection-adsorption spectroscopy, and X-ray photoelectron spectroscopy. The contact angle data showed that the wettabilities of both SAMs were largely similar to each other and to the PEC samples for a wide range of contacting probe liquids (with water correlating particularly well with PEC and both SAMs). As a whole, the wettability data suggest that the carbonate-terminated SAMs can serve as mimics of nanoscale polycarbonate surfaces and can be used to investigate the interfacial properties of polycarbonates without interference from the surface reconstruction.

Mechanically Robust and Chemically Recyclable Polyhydroxyurethanes from CO2-Derived Six-Membered Cyclic Carbonates.

In the current context of sustainable chemistry development and new regulations, aminolysis of cyclic carbonate is one of the most promising routes to nonisocyanate polyurethanes, also called polyhydroxyurethanes (PHU). In this study, a new kind of shape memory PHU vitrimers with outstanding mechanical properties and chemical recyclability is prepared. The monomer employed for aminolysis to form the PHUs is bis(six-membered cyclic carbonate) of 4,4'-biphenol (BCC-BP), which is synthesized by bi(1,3-diol) precursors and CO2. The synthetic strategy, isocyanate-free and employing CO2 as a building block, is environmentally friendly and suits the concept of carbon neutrality. The thermal properties, mechanical properties, and dynamic behaviors of the PHUs are explored. The maximum breaking strength and elongation at break of the resultant PHUs reach 65 MPa and 452%, respectively, exceeding other reported PHU-based materials in combined performance. Such a PHU material can also lift up a load 4700 times heavier than its own weight by a shape recovery process. Finally, the bi(1,3-diol) can be regenerated through the alcoholysis of PHUs to realize chemical recycling. This work provides a feasibility study for a green synthetic approach and for designing a novel PHU material with outstanding properties.

Non-isocyanate polyurethane foams based on six-membered cyclic carbonates

Polyurethane foams currently dominate the global foam market. Nevertheless, the main drawback of these foams remains the use of toxic isocyanate reagents. To overcome this issue, several ways have been explored. The most promising route appears to be the aminolysis of 5-membered cyclic carbonates leading to formation of polyhydroxyurethanes (PHUs). However, the lack of reactivity of systems using C5-cyclic carbonates currently limits the application range of PHUs. Hence, this study reports the first synthesis of PHUs foams using a new tetrafunctional 6-membered cyclic carbonate (TC6). The TC6 was reacted with different diamines under catalyst-free and mild temperature conditions in presence of a chemical blowing agent. Three different amines were employed, allowing access to various foams properties. Finally, promising flexible foams have been obtained, with interesting properties that could make them possible new candidates for applications as seating or insulation mattresses.

Insights on the Atmospheric-Pressure Plasma-Induced Free-Radical Polymerization of Allyl Ether Cyclic Carbonate Liquid Layers.

Plasma-induced free-radical polymerizations rely on the formation of radical species to initiate polymerization, leading to some extent of monomer fragmentation. In this work, the plasma-induced polymerization of an allyl ether-substituted six-membered cyclic carbonate (A6CC) is demonstrated and emphasizes the retention of the cyclic carbonate moieties. Taking advantage of the low polymerization tendency of allyl monomers, the characterization of the oligomeric species is studied to obtain insights into the effect of plasma exposure on inducing free-radical polymerization. In less than 5 min of plasma exposure, a monomer conversion close to 90% is obtained. The molecular analysis of the oligomers by gel permeation chromatography coupled with high-resolution mass spectrometry (GPC-HRMS) further confirms the high preservation of the cyclic structure and, based on the detected end groups, points to hydrogen abstraction as the main contributor to the initiation and termination of polymer chain growth. These results demonstrate that the elaboration of surfaces functionalized with cyclic carbonates could be readily elaborated by atmospheric-pressure plasmas, for instance, by copolymerization.

Cationic living polymerization of cyclic dithiocarbonates involving sulfide-migration

Ring-opening polymerization of cyclic dithiocarbonates was attempted by varying reaction conditions (temperature, concentration, and solvents) to achieve a high polymer conversion. The participation of neighboring sulfide groups in the ring opening was demonstrated by selective sulfide migration and evaluated by composition analysis of the resulting copolymer. The migration was accelerated by electron-enriching substituents on the aryl sulfide and led to the formation of homopolymers with alkyl sulfides. The isomerization of the monomer encountered in the polymerization reduced with sulfide migration and exclusively occurred as substituted by a trityl sulfide. Three catalytic isomerization pathways were proposed for the polymerization mechanism, wherein the electronic and steric contributions of a substituted sulfide group were considered to rationalize the competitive formation of polymers and isomers. The polymerization of a monomer carrying two neighboring groups of butyl sulfide and benzoate proceeded to homopolymerization involving the migration of a sulfide group. The preferential migration was confirmed by the isolation of a six-membered cyclic carbonate as the main fragment product of depolymerization that occurred in the presence of potassium tert-butoxide. A reactive chain end in living polymerization was modified by an in situ reaction with sodium dithiocarbamate. A linear correlation between experimental and theoretical number average molecular weights of the prepared polymers was investigated with polymer conversion variance. The neutralized chain-end improved the chemical stability of the prepared poly(dithiocarbonate)s, and a stable polydispersity was obtained. The thermal decomposition temperature, Td (10% loss), of a polydithiocabonate was measured at 189 °C and the corresponding value after end-capping of the polymer was 285 °C.

One-Pot Nonisocyanate Synthesis of Sequence-Controlled Poly(hydroxy urethane)s from a Bis(six-membered cyclic carbonate) and Two Different Diamines

Sequence-controlled synthetic polymers have received increasing interest because of their great potential to develop next-generation functional materials. Here, we report a facile synthesis of a symmetric spiro bis(six-membered cyclic carbonate), 2,4,8,10-tetraoxaspiro[5.5]undecane-3,9-dione (1), its reactivity, and a one-pot, nonisocyanate synthesis of sequence-controlled poly(hydroxy urethane)s (PHUs) from 1 with two different symmetric diamines. The second-order rate constant for the ring-opening addition reaction of one of the two cyclic carbonates of 1 with 1-hexylamine is two orders of magnitude larger than that of the remaining one of the resulting intermediate due to a remarkable difference between their ring strain energies. This difference in the reactivity enables the selective formation of a diurethane-linked bis(six-membered cyclic carbonate) from the reaction of 1 with a diamine (0.5 equiv). The subsequent addition of a different diamine (0.5 equiv) to the same pot affords sequence-controlled PHUs with an ABAC sequence.

Catalytic Asymmetric Ring-Opening of σ-Symmetric Cyclic Carbonates with Chiral Amino Sulfonamide Catalysts

Enantioselective ring-opening of σ-symmetric six-membered cyclic carbonates with benzyl alcohol catalyzed by 20 mol% of chiral amino sulfonamide catalysts afforded chiral acyclic carbonates in up to 79% ee.

Sustainable synthesis of CO2-derived polycarbonates from d-xylose

Synthetic transformation of d-xylose into a four-membered cyclic ether allows for reactions with CO2 leading to linear polycarbonates by either ring-opening copolymerisation directly or by isolation of a six-membered cyclic carbonate followed by ring-opening polymerisation.

Invoking Side-Chain Functionality for the Mediation of Regioselectivity during Ring-Opening Polymerization of Glucose Carbonates.

The extent of participation of side-chain functionalities during the 1,5,7-triazabicyclo[5.4.0]dec-5-ene (TBD) organobase-catalyzed ring-opening polymerizations (ROP) of six-membered cyclic d-glucose-based carbonates was found to result in significantly different regiochemical outcomes. High regioselectivity was observed for naturally derived poly(4,6-d-glucose carbonate)s (PGCs) containing carbonate side chain substituents in the 2- and 3-positions, whereas regioirregularity was found for analogous PGCs with ether side-chain substituents. The backbone connectivities and structural details of these PGCs were examined through a combination of comprehensive 1D and 2D NMR studies on unimers and dimers, verifying the ring-opening preferences and indicating the contribution of side-chain functionalities in regioselective ROP processes. A molecular understanding of the curious role of side-chain functionalities was demonstrated via density functional theory calculations, revealing stabilization effects of intermolecular hydrogen bonding between the side-chain functionalities and TBD in the transition states. Overall, this work provides fundamental insights into the organocatalytic ROP of these specific six-membered asymmetric cyclic glucose carbonates. More importantly, these findings serve as a foundation for future design strategies that incorporate adjacent functionalities within monomers to act as directing groups and impart molecular interactions that define regiochemical ring-opening.

Organocatalytic Trapping of Elusive Carbon Dioxide Based Heterocycles by a Kinetically Controlled Cascade Process.

A conceptually novel approach is described for the synthesis of six-membered cyclic carbonates derived from carbon dioxide. The approach utilizes homoallylic precursors that are converted into five-membered cyclic carbonates having a β-positioned alcohol group in one of the ring substituents. The activation of the pendent alcohol group through an N-heterocyclic base allows equilibration towards a thermodynamically disfavored six-membered carbonate analogue that can be trapped by an acylating agent. Various control experiments and computational analysis of this manifold are in line with a process that is primarily dictated by a kinetically controlled acylation step. This cascade process delivers an ample diversity of six-membered cyclic carbonates in excellent yields and chemoselectivities under mild reaction conditions.

Biodegradable pH-responsive micelles loaded with 8-hydroxyquinoline glycoconjugates for Warburg effect based tumor targeting

Biodegradable triblock copolymer poly(ethylene glycol)-b-polycarbonate-b-oligo([R]-3-hydroxybutyrate) was prepared via metal-free ring-opening polymerization of ketal protected six-membered cyclic carbonate followed by esterification with bacterial oligo([R]-3-hydroxybutyrate) (oPHB). Amphiphilic triblock copolymer self-organizes into micelles with a diameter of ~25 nm. Acid-triggered hydrolysis of ketal groups to two hydroxyl groups causes an increase in hydrophilicity of the hydrophobic micelle core, resulting in the micelles swell and drug release. oPHB was added as core-forming block to increase the stability of prepared micelles in all pH (7.4, 6.4, 5.5) studied. Doxorubicin and 8-hydroxyquinoline glucose- and galactose conjugates were loaded in the micelles. In vitro drug release profiles in PBS buffers with different pH showed that a small amount of loaded drug was released in PBS at pH 7.4, while the drug was released much faster at pH 5.5. MTT assay showed that the blank micelles were non-toxic to different cell lines, while glycoconjugates-loaded micelles, showed significantly increased ability to inhibit the proliferation of MCF-7 and HCT-116 cells compared to free glycoconjugates. The glycoconjugation of anti-cancer drugs and pH-responsive nanocarriers have separately shown great potential to increase the tumor-targeted drug delivery efficiency. The combination of drug glycoconjugation and the use of pH-responsive nanocarrier opens up new possibilities to develop novel strategies for efficient tumor therapy.

Selective Organocatalytic Preparation of Trimethylene Carbonate from Oxetane and Carbon Dioxide

The organocatalytic coupling of oxetanes and carbon dioxide (CO2) offers a sustainable route to poly(trimethylene carbonate)s and/or functional six-membered cyclic carbonate monomers. This transfor...

Synthesis of Functionalized Cyclic Carbonates through Commodity Polymer Upcycling.

Functionalized cyclic carbonates are attractive monomers for the synthesis of innovative polycarbonates or polyurethanes for various applications. Even though their synthesis has been intensively investigated, doing so in a sustainable and efficient manner remains a challenge. Herein, we propose an organocatalytic procedure based on the depolymerization of a commodity polymer, bisphenol A based polycarbonate (BPA-PC). Different carbonate-containing heterocycles are obtained in good to excellent yields employing BPA-PC as a sustainable and inexpensive source of carbonate, including functionalized six-membered cyclic carbonates.

Efficient Co-delivery of Doxorubicin and Methotrexate by pH-Sensitive Dual-Functional Nanomicelles for Enhanced Synergistic Antitumor Efficacy.

Combination therapy by co-delivering multiple drugs using a single delivery carrier is a promising strategy to achieve a synergistic antitumor effect. In this study, a novel dual-functional block copolymer mPEG-b-poly(TAC-co-ATMC-g-S(CH2)10COOH) was designed and synthesized for co-delivering two kinds of anticancer drugs, methotrexate (MTX) and doxorubicin (DOX). This biodegradable amphiphilic copolymer could spontaneously self-assemble into electronegative nanomicelles with higher micelle stability and lower hemolysis ratio. Besides hydrophobic interactions, electrostatic interactions between the carboxyl groups of 5-allyloxy-1,3-dioxan-2-one (ATMC) with amine groups of DOX, as well as complementary multiple hydrogen-bonding interactions between thymine groups of thymine-functional six-membered cyclic carbonate (TAC) and 2,6-diaminopyridine (DAP) groups of MTX, could contribute to co-delivering DOX/MTX simultaneously with high-efficiency loading without interference with each other. For comparison, DOX alone and MTX alone were also encapsulated into mPEG-b-poly(TAC-co-ATMC-g-S(CH2)10COOH) nanomicelles. All drug-loaded nanomicelles exhibited sustained release properties with a pH sensitivity. Confocal laser scanning microscopy revealed an efficient cell uptake of DOX and MTX delivered by mPEG-b-poly(TAC-co-ATMC-g-S(CH2)10COOH) nanomicelles, while DOX mainly accumulated in nuclei and MTX in cytoplasm after 8 h of incubation. MTT assay further demonstrated an enhanced synergistic antitumor efficacy of DOX/MTX co-loaded nanomicelles. Therefore, DOX/MTX co-loaded mPEG-b-poly(TAC-co-ATMC-g-S(CH2)10COOH) nanomicelles might have attractive potentials in clinical implications for efficient combination chemotherapy.

Zirconium (IV) Acetylacetonate: Ring-Opening Initiator Mediating One-Step Synthesis of Biodegradable Polyacids

Biodegradable polyacid is obtained in one-step ring-opening polymerization (ROP) of carboxylic-acid-functionalized six-membered cyclic carbonate mediated with zirconium (IV) acetylacetonate. Exemplary copolymers with L,L-lactide are described as well. Moreover, zirconium (IV) acetylacetonate is found to be active catalyst of trimethylene carbonate (TMC) ROP in presence of carboxylic acid yielding PTMC end-capped with the acid derivative. Polymerization mechanism is hypothesized demonstrating possibilities of the method in work-saving polycation synthesis and one-step method of conjugate synthesis of well-known biocompatible polyesters and polycarbonates.

Use of Light-Degradable Aliphatic Polycarbonate Nanoparticles As Drug Carrier for Photosensitizer

Aliphatic poly(carbonate)s (APCs) with rapid and controlled degradation upon specific stimulation have great advantages for a variety of biomedical and pharmaceutical applications. In the present work, we reported a new poly(trimethylene carbonate) (PTMC)-based copolymer containing multiple 4,5-dimethoxy-2-nitrobenzyl photo cleavable groups as pendent chains. The six-membered light-responsive cyclic carbonate monomer (LrM) was first prepared from 2-(hydroxymethyl)-2-methylpropane-1,3-diol and 4,5-dimethoxy-2-nitrobenzyl alcohol and then copolymerized with trimethylene carbonate (TMC) by 1,8-diazabicyclo(5.4.0)undec-7-ene (DBU) catalyzed ring-opening polymerization (ROP) to afford the light-responsive polycarbonate (LrPC). The light-triggered decomposition of LrM and LrPC was studied by NMR, UV/vis spectroscopy, and size exclusion chromatography (SEC), as well as ESI-ToF mass spectrometry. Stable monodisperse nanoparticles with hydrodynamic diameter of 100 nm could be formulated from 25% LrPC and 75% poly(lactide- co-glycolide) (PLGA) and applied for the encapsulation of temoporfin. Upon irradiation with UV light these particles displayed a significant decrease of the particle countrate and increased the release rate of temoporfin in comparison to standard PLGA nanoparticles. This work demonstrated that a combination of encapsulation of photosensitizer and light degradation using light-responsive polymers is suitable to enhance photodynamic therapy (PDT).