Regarding Initial Ring Opening of Propylene Oxide in its Copolymerization with CO2 Catalyzed by a Cobalt(III) Porphyrin Complex

Cobalt(III) tetraphenylporphyrin chloride (TPPCoCl) was experimentally proved to be an active catalyst for poly(propylene carbonate) production. It was chosen as a model catalyst in the present work to investigate the initiation step of propylene oxide (PO)/CO₂ copolymerization, which is supposed to be the ring opening of the epoxide. Ring‐opening intermediates ( 1 – 7 ) were detected by using ¹H NMR spectroscopy. A first‐order reaction in TPPCoCl was determined. A combination of monometallic and bimetallic ring‐opening pathways is proposed according to kinetics experiments. Addition of onium salts (e.g., bis(triphenylphosphine)iminium chloride, PPNCl) efficiently promoted the PO ring‐opening rate. The existence of axial ligand exchange in the cobalt porphyrin complex in the presence of onium salts was suggested by analyzing collected ¹H NMR spectra.     

Multinuclear cobalt–salen complexes with phenylene linker for epoxide polymerizations

Di‐ and trinuclear cobalt (Co)–salen complexes with a benzene ring as a rigid linker were explored for epoxide polymerizations. The dinuclear Co–salen complex with a 1,2‐phenylene linker showed higher catalytic activity than the dinuclear Co–salen complex with a 1,3‐phenylene linker and the trinuclear Co–salen complex with a 1,3,5‐benzenetriyl linker for the copolymerization of propylene oxide (PO) with carbon dioxide. A combination of the absolute configuration of the two Co–salen moieties was found to affect its catalytic activity. The optimized dinuclear Co–salen complex with a heterochiral combination demonstrated highest activity and maintained its catalytic activity under a low catalyst concentration. The heterochiral dinuclear Co–salen complex also showed high activity for the copolymerization of PO with cyclic anhydride. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 2150–2159     

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     

A new copolymerization process leading to poly(propylene carbonate) with a highly enhanced yield from carbon dioxide and propylene oxide

Using excessively loaded propylene oxide (PO) as a solvent, the copolymerization of carbon dioxide (CO₂) and PO was carried out with zinc glutarate catalyst, consequently producing poly(propylene carbonate) of high molecular weight in a high yield (64–70 g polymer per gram of catalyst) never achieved before. Both the PO used as solvent and the excessively loaded CO₂ were fully recoverable, respectively, and reusable for their copolymerization, indicating that this is a clean, green polymerization process to convert CO₂ to its polycarbonate. The polymer yield was further improved by scaling up the copolymerization process. Among zinc glutarate catalysts prepared through several synthetic routes, one from zinc oxide delivered the highest yield in the copolymerization. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 1863–1876, 1999     

Synthesis and characterization of highly random copolymer of ϵ-caprolactone and D,L-lactide using rare earth catalyst

Highly random copolymers of ϵ-caprolactone (CL) and D ,L -lactide (LA) were synthesized by a new catalyst system, rare earth chloride–propylene oxide (PO) system. In the presence of propylene oxide, all rare earth chlorides tested are highly effective for the copolymerization. The influences of reaction conditions on the copolymerization catalyzed by the NdCl₃-5PO system have been investigated in detail. The reactivity ratios of ϵ-caprolactone and D ,L -lactide were determined and show that the copolymerization with this new rare earth catalyst is closer to ideal copolymerization than reported for other catalysts. The microstructure of copolymer analyzed by ¹³C-NMR shows that the monomer units in the copolymer is near to completely random distribution with a short average monomer sequence length. The DSC measurement confirms the high randomness of the chain structure. The mechanism studied by NMR indicates that the rare earth alkoxide generated by the reaction of rare earth chloride with propylene oxide initiates the copolymerization, and then proceeds via a “coordination-insertion” mechanism with acyl-oxygen bond cleavage of CL and LA. © 1996 John Wiley & Sons, Inc.     

Alternating Copolymerization of Propylene Oxide with Biorenewable Terpene‐Based Cyclic Anhydrides: A Sustainable Route to Aliphatic Polyesters with High Glass Transition Temperatures

The alternating copolymerization of propylene oxide with terpene‐based cyclic anhydrides catalyzed by chromium, cobalt, and aluminum salen complexes is reported. The use of the Diels–Alder adduct of α‐terpinene and maleic anhydride as the cyclic anhydride comonomer results in amorphous polyesters that exhibit glass transition temperatures (T_g) of up to 109 °C. The polymerization conditions and choice of catalyst have a dramatic impact on the molecular weight distribution, the relative stereochemistry of the diester units along the polymer chain, and ultimately the T_g of the resulting polymer. The aluminum salen complex exhibits exceptional selectivity for copolymerization without transesterification or epimerization side reactions. The resulting polyesters are highly alternating and have high molecular weights and narrow polydispersities.     

Copolymerization of carbon dioxide and propylene oxide by several metallosalen‐based bifunctional catalysts

A series of new metallosalen‐based bifunctional catalysts with Co(III), Cr(III), Fe(III), Mn(III), and Ni(III) were synthesized for the first time, and a detailed study on the mechanism of the copolymerization of CO₂ and propylene oxide (PO) was performed. Meanwhile, the impact factors of the reaction conditions (metal cations, temperature, CO₂ pressure, and reaction time) on catalytic activity and selectivity were investigated. The results indicated that, with the increase of temperature, both the catalyst efficiency and the molecular weight of the copolymer decrease for all the five complexes. The salen‐Co(III) complex demonstrated higher activity under mild conditions: reaction temperature at 30 °C, copolymerization time of 24 hr, and 2 MPa of CO₂ pressure. The DSC curve indicated that the PPC by the salen‐Co(III) complex has the highest T_g of 46.19 °C. DTGA curves demonstrated that there were two thermal degradation peaks: the first is for the ester bond, and the second is for the C C bond.     

Some aspects of the bimetallic μ-oxo-alkoxides for polymerizing epoxides to polyether elastomers

The bimetallic catalysts of Osgan and Teyssie, (RO)₂Al-O-Zn-O-Al(OR)₂, are effective, unusual catalysts for polymerizing epoxides. The polymer obtained from propylene oxide when R = n-Bu is preponderantly isotactic and highly crystalline and thus, largely head-to-tail. Crystallizable, sulfur vulcanizable propylene oxide rubber was made by copolymerizing propylene oxide (PO) with allyl glycidyl ether (AGE) with this catalyst. This product after S vulcanization exhibited gum tensile and other properties which were superior to the commercially available, amorphous PO–AGE copolymer of similar composition. However, the Osgan–Teyssie catalyst is very sensitive to reactive, polar impurities. Hindered alkyl aluminums and especially alkoxides such as Et₂AlOtert–Bu can be added to help alleviate this problem. The reported favorable (but slow) copolymerization of epichlorohydrin with propylene oxide in nonpolar media with the Osgan–Teyssie catalyst has been confirmed and an alternate explanation for this unusual result suggested.     

Copolymerization of Carbonyl Sulfide and Propylene Oxide via a Heterogeneous Prussian Blue Analogue Catalyst with High Productivity and Selectivity

This study demonstrates the superiority of a stable and well-defined heterogeneous cobalt hexacyanocobaltate (Co₃[Co(CN)₆]₂), a typical cobalt Prussian Blue Analogue (CoCo-PBA) that catalyzes the copolymerization of carbonyl sulfide (COS) and propylene oxide (PO) to produce poly(propylene monothiocarbonate)s (PPMTC). The number-average molecular weights of the PPMTC were 66.4 to 139.4 kg/mol, with a polydispersity of 2.0–3.9. The catalyst productivity reached 1040 g polymer/g catalyst (12.0 h). The oxygen-sulfur exchange reaction (O/S ER), which would generate random thiocarbonate and carbonate units, was effectively suppressed, and thus the selectivity of the monothiocarbonate over carbonate linkages was up to >99%. It was shown that no cyclic thiocarbonate byproduct was produced during the heterogeneous catalysis of COS/PO copolymerization using CoCo-PBA as the catalyst. The content of monothiocarbonate and ether units in the copolymer chain could be regulated by tuning the feeding amount of COS.     

铝卟啉配合物催化二氧化碳与环氧丙烷共聚反应

铝卟啉是一类土壤环境友好的金属卟啉,尽管早在1978年Inoue就已经发现它可以催化CO₂和环氧丙烷的共聚反应,但是该催化体系一直面临催化活性低、聚合物相对分子质量低等难题。 本文通过改变铝卟啉催化剂配体中苯环上取代基的种类和位置,制备出中心金属电子环境差异化的铝卟啉,并以双三苯基膦氯化铵(PPNCl)为助催化剂,探讨其对CO₂与环氧丙烷的共聚反应的催化行为。 结果表明,当铝卟啉中苯环上2,4位同时被Cl^-取代后,在90 ℃和3 MPa压力下,转化频率(TOF)达到2672 h^-1。 当利用离去能力较强的对甲苯磺酸基团(OTs^-)作为铝卟啉的轴向配体,可以合成出数均相对分子质量达1.84×10⁵的脂肪族聚碳酸酯。     

Steric hindrance ligand strategy to aluminum porphyrin catalyst for completely alternative copolymerization of CO2 and propylene oxide

Aluminum porphyrin complexes are heavy-metal-free and soil-tolerant green catalysts for the copolymerization of CO2 and propylene oxide (PO),but they suffer from relatively poor poly(propylene carbonate) (PPC) selectivity.Herein,steric hindrance porphyrin ligand was used to enhance the PPC selectivity.Typically,a bulky anthracene-like group was incorporated into the porphyrin ring to form 5,10,15,20-tetra(1,2,3,4,5,6,7,8-octahydro-1,4:5,8-dimethanoanthracen-9-yl)porphyrin,the aluminum porphyrin complex with this ligand,in combination with bis(triphenylphosphine)iminium chloride as a co-catalyst,produced completely alternate PPC.Additionally,the obtained PPC showed high regioselectivity,with a head-to-tail linkage content (HT) of 92％.Therefore,we demonstrated that introduction of bulky steric ligand into the porphyrin ring could reduce the propylene oxide homopolymerization activity leading to excellent PPC selectivity,and improve regioselectivity for the PO ring-opening during the copolymerization.     

Temperature‐responsive Catalyst for the Coupling Reaction of Carbon Dioxide and Propylene Oxide

The selective synthesis of polypropylene carbonate (PPC) and cyclic propylene carbonate (CPC) from coupling reaction of CO₂ and propylene oxide (PO) is a long term pursuing target. Here we report that a temperature controllable porphyrin aluminum catalyst using 5,10,15,20‐tetra(1,2,3,4,5,6, 7,8‐octahydro‐1,4:5,8‐dimethanoanthracen‐9‐yl)porphyrin as ligand, once in conjunction with suitable onium salt, achieved single cycloaddition or copolymerization reaction. Only cycloaddition reaction happened at temperature above 75 °C to produce 100% CPC, whereas copolymerization became dominant to afford PPC with selectivity over 99% at 25 °C, and the obtained PPC showed over 99% carbonate linkage and 92% head‐to‐tail structure. Based on systematic analysis of the electronic and steric feature in the porphyrin ligand, it was found that the electronic feature of the substituent in porphyrin ligand was decisive for PPC selectivity, porphyrin ligand bearing strong electron‐donating substituents displayed a significantly reduced tolerance towards increased temperature with respect to PPC formation. Therefore, temperature‐responsive catalyst could be designed by suitable modification in porphyrin ligand, and such accurate synthesis of target product by one catalyst may create a useful and facile platform for selective PPC or CPC production.     

Catalytic asymmetric addition of carbon dioxide to propylene oxide with unprecedented enantioselectivity

New chiral catalyst systems were developed for the reaction of carbon dioxide with propylene oxide (PO) at atmospheric pressure to generate enantiomerically enriched propylene carbonate (PC). The best selectivity was achieved with a Co(III)(salen)-trifluoroacetyl complex and bis(triphenylphosphoranylidene)ammonium fluoride (PPN+F-) as catalysts, affording PC in 40% yield and 83% ee (selectivity factor = 19). In addition, PC was prepared for the first time by kinetic resolution of PO with tetrabutylammonium methyl carbonate (TBAMC, nBu4N+ (-)OOCOMe). With TBAMC as "activated CO2", up to 71% ee was obtained.     

Perfectly alternating copolymerization of CO2 and epichlorohydrin using cobalt(III)-based catalyst systems

Selective transformations of carbon dioxide and epoxides into biodegradable polycarbonates by the alternating copolymerization of the two monomers represent some of the most well-studied and innovative technologies for potential large-scale utilization of carbon dioxide in chemical synthesis. For the most part, previous studies of these processes have focused on the use of aliphatic terminal epoxides or cyclohexene oxide derivatives, with only rare reports concerning the synthesis of CO(2) copolymers from epoxides containing electron-withdrawing groups such as styrene oxide. Herein we report the production of the CO(2) copolymer with more than 99% carbonate linkages from the coupling of CO(2) with epichlorohydrin, employing binary and bifunctional (salen)cobalt(III)-based catalyst systems. Comparative kinetic studies were performed via in situ infrared measurements as a function of temperature to assess the activation barriers for the production of cyclic carbonate versus copolymer involving two electronically different epoxides: epichlorohydrin and propylene oxide. The relative small activation energy difference between copolymer versus cyclic carbonate formation for the epichlorohydrin/CO(2) process (45.4 kJ/mol) accounts in part for the selective synthesis of copolymer to be more difficult in comparison with the propylene oxide/CO(2) case (53.5 kJ/mol). Direct observation of the propagating polymer-chain species from the binary (salen)CoX/MTBD (X = 2,4-dinitrophenoxide and MTBD = 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene) catalyst system by means of electrospray ionization mass spectrometry confirmed the perfectly alternating nature of the copolymerization process. This observation in combination with control experiments suggests possible intermediates involving MTBD in the CO(2)/epichlorohydrin copolymerization process.     

DFT studies on the origin of regioselective ring-opening of terminal epoxides during copolymerization with CO<Subscript>2</Subscript>

This report presents a detailed density functional theory（DFT） study on the difference in regioselectivity for the copolymerization reactions of styrene oxide versus propylene oxide with CO₂ utilizing binary（salen）cobalt（Ⅲ） catalyst systems. This study focuses on the discrepancy of regioselective ring-opening of two terminal epoxides during the copolymerization with CO₂. It was found that the nucleophilic ring-opening of styrene oxide occurred predominantly at the methine C_a―O bond due to the election delocalization of phenyl group to stabilize the transition state for the methine C―O bond cleavage.     

High yield synthesis of biodegradable poly(propylene carbonate) from carbon dioxide and propylene oxide

A novel SalenCo^III (2,4‐dinitrophenoxy) (Salen = N,N'‐bis(3,5‐di‐tert‐butylsalicylidene)‐1,2‐cyclohexanediamino) and 1,10‐phenanthroline monohydrate catalyst system was designed and employed for the copolymerization of CO₂ and propylene oxide (PO). The perfectly alternating copolymerization of CO₂ and PO proceeds effectively under middle temperature and pressure to yield poly(propylene carbonate) with a high yield and a high number average molecular weight of polymer. The structure of polymer was characterized by the IR and NMR measurements. The perfectly alternating copolymer was confirmed. The MALDI‐TOF spectrum insinuates that the copolymerization of CO₂ and PO was initiated by H₂O. Copyright © 2016 John Wiley & Sons, Ltd.     

The influence of reagent concentration on the kinetics of carbon dioxide-propylene oxide copolymerization in the presence of a cobalt complex

The effect of the concentrations of propylene oxide and the catalyst (salen)CoDNP/[PPN]Cl ((salen)CoDNP: [PPN]Cl = 1: 1, mol/mol) on the kinetics of the copolymerization of CO₂ and propylene oxide at 0.5 MPa and 20°C has been studied. The reaction proceeds at a constant rate after an induction period, and the value of this period varies with the reagent concentrations. The steady-state reaction rate increases linearly with the propylene oxide concentration in the range 5.0–14.3 mol/L. At high catalyst concentrations, such as (5.2–7.3) × 10^?3 mol/L, the reaction rate is first order in the catalyst; at concentrations below 5 × 10^?3 mol/L, the reaction rate is second order in the catalyst. Molecular mass increases in proportion to the propylene oxide conversion, that is consistent with a living polymerization process. A regioregular copolymer with 96% head-to-tail (HT) connectivity of propylene oxide has been obtained.     

Effects of the structure and morphology of zinc glutarate on the fixation of carbon dioxide into polymer

Zinc glutarates were synthesized from zinc oxides with varying purities via different stirring routes. The particle size and structure of these zinc glutarates were determined by wide‐angle X‐ray diffraction, transmission electron microscopy, and the laser particle size analyzer technique. The results demonstrated that the crystallinity and crystalline perfectness of zinc glutarate are the crucial factors that affect the catalytic activity for the copolymerization of carbon dioxide (CO₂) and propylene oxide (PO). Additionally, the catalyst with a small particle size dramatically increased the yield of the copolymerization between CO₂ and PO. High‐molecular‐weight and regular molecular structure poly(propylene carbonate)s (PPC)s were obtained from CO₂ and PO with the synthesized zinc glutarates. Very high catalytic activity of 160.4 g polymer/g catalyst was afforded. The NMR technique revealed that the PPC copolymer exhibits an exact alternating copolymer structure. The relationships between the crystallinity and the particle size of catalyst with the catalytic activity are correlated and discussed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3579–3591, 2002     

Asymmetric,regio‐ and stereo‐selective alternating copolymerization of CO2 and propylene oxide catalyzed by chiral chromium Salan complexes

Chiral chromium complexes of tetradentate N,N′‐disubstituted bis(aminophenoxide) (designated as Salan, a saturated version of Schiff‐base Salen ligand) in conjunction with an ionic quaternary ammonium salt can efficiently catalyze the copolymerization of CO₂ with racemic propylene oxide (rac‐PO) at mild conditions to selectively afford completely alternating poly(propylene carbonate) (PPC) with ～ 95% head‐to‐tail linkages and moderate enantioselectivity. These new catalyst systems predominantly exceed the previously much‐studied SalenCr(III) systems in catalytic activity, polymer enantioselectivity, and stereochemistry control. The chiral diamine backbone, sterically hindered substitute groups on the aromatic rings, and the presence of sp³‐hydridized amino donors and its N,N′‐disubstituted groups in chiral SalanCr(III) complexes all play significant roles in controlling polymer stereochemistry and enantioselectivity. Furthermore, a relationship between polycarbonate enantioselectivity and its head‐to‐tail linkages in relation to regioselective ring‐opening of the epoxide was also discussed on the basis of stereochemical studies of PPCs derived from the copolymerization of CO₂ with chiral PO at various conditions. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 6102–6113, 2008