Alternating copolymerization of carbon dioxide and epoxide catalyzed by an aluminum Schiff base–ammonium salt system

The alternating copolymerization of carbon dioxide (CO₂) and cyclohexene oxide (CHO) with an aluminum Schiff base complex in conjunction with an appropriate additive as a novel initiator is demonstrated. A typical example is the copolymerization of CO₂ and CHO with the (Salophen)AlMe ( 1a )–tetraethylammonium acetate (Et₄NOAc) system. When a mixture of the 1a –Et₄NOAc system and CHO was pressurized by CO₂ (50 atm) at 80 °C in CH₂Cl₂, the copolymerization of CO₂ and CHO took place smoothly and produced a high polymer yield in 24 h. From the IR and NMR spectra, the product was characterized to be a copolymer of CO₂ and CHO with an almost perfect alternating structure. The matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry analysis indicated that an unfavorable reaction between Et₄NOAc and CH₂Cl₂ and a possible chain‐transfer reaction with concomitant water occurred, and this resulted in the bimodal distribution of the obtained copolymer. With carefully predried reagents and apparatus, the alternating copolymerization in toluene gave a copolymer with a unimodal and narrower molecular weight distribution. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4172–4186, 2005     

Alternating copolymerization of carbon dioxide and epoxide by manganese porphyrin: The first example of polycarbonate synthesis from 1-atm carbon dioxide

The first successful example of the formation of polycarbonate from 1-atm carbon dioxide and epoxide was demonstrated by the alternating copolymerization of carbon dioxide and epoxide with manganese porphyrin as a catalyst. The copolymerization of carbon dioxide and cyclohexene oxide with (porphinato)manganese acetate proceeded under the 1-atm pressure of carbon dioxide to give a copolymer with an alternating sequence. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 3549–3555, 2003     

Copolymerization of carbon dioxide and cyclohexene oxide catalyzed by chromium complexes bearing semirigid [ONSO]‐type ligands

Chromium complexes supported by tetradentate dianionic imine‐thioether‐bridged bis(phenol) ligands were prepared and employed in the synthesis of poly(cyclohexene carbonate) via the copolymerization of CO₂ and cyclohexene oxide. The catalytic activity, product selectivity, and kinetic behaviors of these [ONSO]Cr^III complexes have been systematically investigated. Results indicate the presence of electron‐withdrawing substituents on the ligands to enhance catalytic activity and polymer selectivity. A turnover frequency of 100 h^?1 is observed at a temperature of 110 °C, producing polycarbonate with >60% selectivity. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1938–1944     

Copolymerization of carbon dioxide and cyclohexene oxide with zinc/β‐ketoiminato complexes: Investigating the influence of the electron structure of zinc/β‐ketoiminato complexes on the catalytic activity and resultant copolymer properties

A series of LZnX zinc/β‐ketoiminato complexes [L = CH₃C(OH)?C(CH₂CH?CH₂)C(CH₃)?NAr ( L₁ ), CH₃C(OH)?C(CH₂CH₂CN)C(CH₃)?NAr ( L₂ ), CH₃C(OH)?C(CH₂C₆H₅)C(CH₃)?NAr ( L₃ ), or CH₃C(OH)?CHC(CH₃)?NAr ( L₄ ); Ar = 2,6‐ⁱPr₂C₆H₃; and initiation group X = alcoholate or acetate (for L₁ ) or alcoholate (for L₂ – L₄ )] were synthesized, and their activities toward the copolymerization of carbon dioxide with cyclohexene oxide were determined. The 3‐position substituents on the β‐ketoiminato ligand backbone of the zinc/β‐ketoiminato complexes played an important role not only in the catalytic activity but also in the intrinsic viscosity, chemical composition, and refined microstructure of the resultant copolymers. The order of the catalytic activity of L₁ ZnX with different initiation groups (X = OMe, OⁱPr, or OAc) was L₁ Zn (OⁱPr) > L₁ Zn (OMe) > L₁ Zn (OAc), being the opposite of the order of the leaving ability of the initiation groups. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6243–6251, 2006     

Polymer cyclization inhibits thermal decomposition of carbon‐dioxide‐derived poly(propylene carbonate)s

Remarkable enhancement of CO₂‐derived poly(propylene carbonate) (PPC) against thermal decomposition was achieved by cyclization of linear PPCs. Thus, a CO₂‐derived linear vinyl‐telechelic PPC was synthesized by CO₂–propylene oxide alternating copolymerization initiated from H₂O followed by an end‐capping esterification with 4‐pentenoic acid. Cyclic PPC was synthesized by the end‐to‐end intramolecular reaction of the vinyl‐telechelic linear PPC by metathesis condensation. Comparison of the thermal decomposition temperature (T_d) with linear and cyclic PPCs confirms surprisingly enhanced T_ds of cyclic PPCs. The elimination of chain ends through cyclization is indeed valuable for enhancing T_d of CO₂‐derived PPCs and thus turn the spotlight on the materials design utilizing CO₂. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3336–3342     

Development of a Halide‐Free Aluminium‐Based Catalyst for the Synthesis of Cyclic Carbonates from Epoxides and Carbon Dioxide

Kinetic studies of the synthesis of glycerol carbonate from glycidol and carbon dioxide have been carried out. These showed that under suitable reaction conditions, bimetallic aluminium(salen) complex 4 is able to catalyse the conversion of epoxides into the corresponding cyclic carbonates without the need for a co‐catalyst.     

Preparation of double metal cyanide compleces from water-insoluble zinc compounds and their catalytic performance for copolymerization of epoxide and CO2

A novel method was developed for preparing double metal cyanide complexes based on Zn₃[Co(CN)₆]₂ with water-insoluble zinc compounds such as ZnO, Zn(OH)₂ and basic ZnCO₃ as precursors. The complexes obtained exhibited nearly double catalytic efficiency for the copolymerization of propylene oxide and CO₂ as compared with the complexes originating from the solution precipitation method.     

Bifunctional cobalt Salen complex: a highly selective catalyst for the coupling of CO2 and epoxides under mild conditions

A bifunctional cobalt Salen complex containing a Lewis acid metal center and two covalent bonded Lewis bases on the ligand was designed and used for the coupling of CO₂ and epoxides under mild conditions. The complex exhibited excellent activity (turnover frequency = 673/h) and selectivity (no less than 97%) for polymer formation in the copolymerization of propylene oxide (PO) and CO₂ at an appropriate combination of all variables. High molecular weight of 110 200 and yield 99% were achieved at a higher [PO]/[complex] ratio of 6000:1. The complex also worked satisfactorily for the terpolymerization of CO₂, PO and cyclohexene oxide (CHO), without formation of cyclic carbonate or ether linkages to give the polycarbonate. High cyclohexene carbonate unit content in the CO₂/PO/CHO terpolymers resulted in enhanced thermal stability. Copyright © 2011 John Wiley & Sons, Ltd.     

Alternating copolymerization of carbon dioxide and propylene oxide under bifunctional cobalt salen complexes: Role of Lewis base substituent covalent bonded on salen ligand

Alternating copolymerization of propylene oxide (PO) and carbon dioxide (CO₂) was realized under mild conditions with a moderate turnover frequency (TOF), employing sole bifunctional cobalt salen complexes containing Lewis acid metal center and covalent bonded Lewis base on the ligand. Variation of the covalent bonded Lewis base substituents on the salen ligands could tailor the catalytic activity with TOF changing from 19.3 to 34.9 h^?1, polymeric/cyclic carbonate selectivity from 95.3 to 72.8%, and the head‐to‐tail structure in the polymer from 72.2 to 86.0%. The IR analysis confirmed that the Lewis base moiety on one molecule could coordinate with cobalt center of adjacent molecule, playing similar role to the Salen metal complex/Lewis base binary catalytic system. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 359–365, 2010     

DMAP/Cr(III) Catalyst Ratio: The Decisive Factor for Poly(propylene carbonate) Formation in the Coupling of CO2 and Propylene Oxide

Highly efficient formation of poly(propylene carbonate) can be achieved in the coupling of CO₂ and propylene oxide assisted by 4‐(N,N‐dimethylamino)pyridine (DMAP) and catalyzed with salen chromium(III) chloride by using DMAP/Cr ratios of less than 2. Under these conditions a possible backbiting mechanism is suppressed, leading to only minor amounts of cyclic carbonate as a side product.

     

Copolymerization of carbon dioxide and epoxide

An erratum has been published for this article in J Polym Sci Part A: Polym Chem (2005) 43(4) 916 . The alternating copolymerization of carbon dioxide and epoxide to produce polycarbonate has attracted the attention of many chemists because it is one of the most promising methodologies for the utilization of carbon dioxide as a safe, clean, and abundant raw material in synthetic chemistry. Recent development of catalysts for alternating copolymerization is based on the rational design of metal complexes, particularly complexes of transition metals with well‐defined structures. In this article, the history and recent successful examples of the alternating copolymerization of carbon dioxide and epoxide are described. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5561–5573, 2004     

Double metal cyanide complex based on Zn3[Co(CN)6]2 as highly active catalyst for copolymerization of carbon dioxide and cyclohexene oxide

Double metal cyanide complexes based on Zn₃[Co(CN)₆]₂ were prepared in the presence of different complexing agents and used in the copolymerization of carbon dioxide and cyclohexene oxide. The FTIR and ¹H NMR spectra of the products verified the formation of polycarbonate. Compared with zinc carboxylate, zinc phenoxide, and so forth, these catalysts demonstrated great enhancement of catalytic activity. Their highest turnover number and turnover frequency reached 3300 and 1650 h^?1, respectively, at 90 °C. The molar fraction of CO₂ (F_CO2) for the copolymers was about 0.44–0.47, and it varied slightly with different catalysts under a temperature of 90 °C and a pressure of 3.8 MPa. The study showed that the F_CO2 can reach 0.40 even at 0.6 MPa, and it changed slightly above 3.8 MPa. The reaction rate had little influence on the F_CO2 under our experimental conditions. A relatively low temperature was favorable for the incorporation of CO₂. The monitoring of copolymerization revealed the molecular weight was proportional to the reaction conversion. The molecular weight distribution was in the range of 4.5–6, and the reaction rate was proportional to the amount of catalyst that was used. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 5284–5291, 2004     

Bifunctional aluminum porphyrin complex: Soil tolerant catalyst for copolymerization of 2 and propylene oxide

Due to the concern on residue toxic metal in biodegradable poly(propylene carbonate) (PPC), soil tolerant and heavy metal free aluminum complexes, that is, bifunctional aluminum porphyrin catalysts bearing quaternary ammonium salts on the ligand framework were prepared. Variation of the quaternary ammonium anion and the axial ligand had dramatic effects on the catalytic activity of resultant complex, among which complex 3b yielded perfectly alternative PPC with high molecular weight and relatively narrow polydispersity, and its TOF reached 3,407 h^?1 at [PO]/[cat.] ratio of 20,000 at 110 °C, although the PPC selectivity was 71%. By introducing specific substituent on the ligand framework, the electronic environment at the active center can be changed, among which complex 5b bearing tertiary butyl‐functionalized aryl substituents exhibited a TOF of 449 h^?1 at [PO]/[cat.] ratio of 5,000 at 70 °C, with PPC selectivity of 92% and number average molecular weight of 36 kg mol^?1. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2346–2355     

Alternating copolymerization of carbon dioxide and cyclohexene oxide catalyzed by silicon dioxide/Zn?CoIII double metal cyanide complex hybrid catalysts with a nanolamellar structure

Air‐stable hybrid catalysts of silicon dioxide/double metal cyanide complexes (Si‐DMCCs) based on Zn₃[Co(CN)₆]₂ (ZHCC) were prepared by an in situ sol–gel method. The Si‐DMCCs showed low crystallinity and a nanolamellar structure with a thickness of ～40–60 nm. In particular, a lamellar structure of regular hexagonal shape was observed for Si‐DMCCs with low SiO₂ content. These catalysts had very high catalytic activity for alternating copolymerization of cyclohexene oxide (CHO) and carbon dioxide. A turnover number of 11,444, turnover frequency of 3815 h^?1, and apparent efficiency of 7.5 kg polymer/g ZHCC (～24.0 kg polymer/g Zn) were achieved at 3.8 MPa and 100 °C. The poly(cyclohexenylene carbonate) (PCHC) polymers obtained were completely atactic with a molecular weight (M_n) of ～10 kg/mol and polydispersity of 2.0–3.0. The PCHCs had a structure of nearly alternating CHO and CO₂ units, with a molar fraction of carbonate units of 0.44–0.47. Preliminary investigations of the mechanism suggest that nucleophilic attack by neighboring oxygen atoms is involved in copolymerization initiation with Zn? Co^III DMCCs. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3128–3139, 2008     

Cycloaddition of epoxide and CO2 to cyclic carbonate catalyzed by VO(IV) porphyrin

The cycloaddition of epoxide and CO₂ to synthesize cyclic carbonate catalyzed by VO(IV) porphyrin was achieved under 1.4 MPa at 150°C. The effects of reaction temperature, time, CO₂ pressure, co‐catalyst and porphyrin framework were investigated. The catalytic results showed that moderate to high yields of cyclic carbonates were obtained under the optimal reaction conditions. Copyright © 2015 John Wiley & Sons, Ltd.     

Cobalt(III)‐complex‐mediated terpolymerization of CO2, styrene oxide,and epoxides with an electron‐donating group

Terpolymerizations of CO₂, styrene oxide (SO), and epoxides with an electron‐donating group such as propylene oxide (PO) or cyclohexene oxide (CHO) were carried out by using Co(III)–salen complexes in the presence of an intra‐ or intermolecular nucleophilic cocatalyst. The resultant terpolymers have only one thermolysis peak and one glass transition temperature (T_g), which can be easily adjusted by controlling the proportion of styrene carbonate linkages. During the CO₂/SO/PO terpolymerization, the monomer reactivity ratios (r_SO = 0.18 and r_PO = 2.25) evaluated by Fineman–Ross plot indicates a random distribution of the two kinds of carbonate units in the resultant polymer. Contrarily, the monomer reactivity ratios were found to be r_SO = 0.48 and r_CHO = 0.79 in the CO₂/SO/CHO terpolymerization, indicating that an alternating nature of the two different carbonate units predominantly exists in the resultant polycarbonate. The regioselective ring opening of SO has a significant effect on the reactivities of both SO and CHO during the terpolymerization with CO₂. The matched reactivity is contributed to the enhanced regioselective ring opening of SO, caused by the attack of the dissociating polymer carboxylate anion, bearing a cyclohexene carbonate end unit. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2013     

Construction of Versatile and Functional Nanostructures Derived from CO2‐based Polycarbonates

The construction of amphiphilic polycarbonates through epoxides/CO₂ coupling is a challenging aim to provide more diverse CO₂‐based functional materials. In this report, we demonstrate the facile preparation of diverse and functional nanoparticles derived from a CO₂‐based triblock polycarbonate system. By the judicious use of water as chain‐transfer reagent in the propylene oxide/CO₂ polymerization, poly(propylene carbonate (PPC) diols are successfully produced and serve as macroinitiators in the subsequent allyl glycidyl ether/CO₂ coupling reaction. The resulting ABA triblock polycarbonate can be further functionalized with various thiols by radical mediated thiol–ene click chemistry, followed by self‐assembly in deionized water to construct a versatile and functional nanostructure system. This class of amphiphilic polycarbonates could embody a powerful platform for biomedical applications.