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Synthesis of degradable sulfur-containing polymers via the copolymerization of SO2 with epoxides or olefines.

Aliphatic polyethers are one of the most widely used polymers, whose synthesis is largely dependent on metallic compounds. Recent development of organocatalysts may break the limits of this long-standing field and infuse vitality into polyether production. In this Synpacts article, the recent advances of organocatalysts for polyether production is introduced in aspects of catalytic performance and mechanism. Moreover, attentions are paid to the latest contributions of bifunctional organoboron catalysts which can be prepared with high yields from cost-effective raw materials in two facile reactions and show excellent performance in the polyether production with remarkable catalytic efficiency, controllability on molecular weight, and explicit polymerization mechanism. Based on these advances, it is envisioned that new discoveries using organocatalysts will continue in the foreseeable future.1 Introduction2 Challenges in Metallic Catalysts3 Previous Advances in Organocatalysts4 Recent Contributions of Bifunctional Organoboron Catalysts5 Conclusion

The development of a controlled and reliable method to construct well-defined sulfur-containing polymers has sparked great interest in polymer science. Herein, we present the trial on the copolymerization of isothiocyanates with episulfides in the presence of organic onium salts, which provides direct access to a class of sulfur-rich polymers. This methodology has combined advantages of simple operation, no metals, mild conditions (25-100 °C), controlled polymerization performance (

A highly stereoregular polyphosphoester with a rigid cyclohexylene structure in the main chain was constructed via ring-opening polymerization (ROP) in the presence of an organic catalyst system. Differential scanning calorimetry (DSC) analysis indicated that isotactic polyphosphoesters exhibit a higher glass transition temperature (Tg = 9.9 °C) compared with their atactic counterparts (−20.6 °C), which are much higher than that (−60 to −40 °C) of the previously reported phosphate polymers, making these polymers have great potential in materials science.

Weak segregation of polystyrene-block-poly(methyl methacrylate) block copolymers (PS-b-PMMA BCPs) limits their utility for sub-10 nm lithography. Such limits could be overcome by including ionic li...

The performances of lithium-ion batteries (LIBs) are dependent on the wettability and stability of porous separators. Musselinspired coatings seem to be useful to improve the surface wettability of commercialized polyolefin separators. However, it is still a challenge to guarantee their stability under polar electrolytes. Herein, we report a facile and versatile way to enhance the wettability and stability of polypropylene separators by constructing robust polydopamine (PDA) coatings triggered with CuSO4/H2O2. These coatings were conveniently deposited on the polypropylene separator surfaces and the PDA-coated separators exhibited the improved surface wettability and thermal stability. The electrolyte uptake increased nearly two folds from the pristine separator to the modified ones. Correspondingly, the ionic conductivity also rose from 0.82 mS·cm-1 to 1.30 mS·cm-1. Most importantly, the CuSO4/H2O2-triggered PDA coatings were very stable under strong polar electrolytes, endowing the cells with excellent cycle performance and enhanced C-rate capacity. Overall, the results unequivocally demonstrate that application of PDA coatings on polyolefin separator triggered by CuSO4/H2O2 is a facile and efficient method for improving the wettability and stability of separators for high LIBs performance.

The first example of CO2-based thermoset elastomers (CO2Es) on the basis of two sustainable and degradable polymers, rigid CO2-based polycarbonates and soft polyesters, is reported. The elastomers exhibit acceptable mechanical strength and excellent elasticity (average elastic recovery >93%) by introducing a chemical network. By adjusting the ratio of rigid CO2 polycarbonate/soft polyester, green elastomers with adjustable mechanical performance are obtained efficiently.

The copolymerization of carbon dioxide (CO2) with epoxides via organocatalysis is still a big challenge. This work reports the selective copolymerization of CO2 and epoxides bearing a phenyl group, i.e., phenyl glycidyl ether (PGE) and styrene oxide (StO), catalyzed by a combination of Lewis bases (LBs) and excess triethyl borane (TEB). The resultant CO2/PGE copolymers presented a molar fraction of carbonate units (FCO2) of more than 99%, with a regioregularity of ca. 92%. The weight percentage of the cyclic carbonate (WCC) was less than 1 wt%. The turnover frequency (TOF) was as high as 38 h−1 for producing the CO2/PGE copolymer with a number-average molecular weight (Mn) of 16.6 kg mol−1 and a dispersity (Đ) of 1.2. What is of importance is that the dosage of TEB had a strong impact on the selectivity, where the regioregular copolymer or cyclic carbonate could be selectively produced by simply tuning the TEB/LB molar ratios, as revealed by in situ FT-IR spectroscopy. It is proposed that excess TEB could either promote the equilibrium to generate the TEB-coordinated growing anion or activate the epoxide for enhancing the reactivity. Both copolymers are promising optical materials as colorless solids with a high refractive index (nd) of 1.55–1.56 (590 nm, 20 °C, cast film).

Construction of block copolymers is a practical method for modifying the properties of CO2-based polycarbonates (CO2-PCs) in order to meet specific needs. Herein, we report a well-defined single-site β-diiminate zinc complex 1 equipped with the capacities of coordination copolymerization of CO2/epoxide and reversible addition–fragmentation chain transfer (RAFT) polymerization of vinyl monomers. Complex 1 is specifically designed to possess a 3-(benzylthiocarbonothioylthio)propionate (BSTP) initiating group, which enables the controlled ring-opening copolymerization of epoxides and CO2, leaving a polycarbonate with BSTP functional group at the end of the chain. The end-capped BSTP allows direct chain extension via living RAFT polymerization, thus providing a robust method to construct various CO2-based block copolymers in one pot via a tandem catalysis strategy. The structure of 1 is established by single-crystal X-ray diffraction as well as 1H and 13C NMR. By utilizing 1, a wide range of CO2-based block c...

The coupling of epoxides and carbon dioxide to polycarbonates (CO2–PCs) has been the subject of intense research for nearly half a century. Although tremendous progress has been achieved, their aliphatic characteristics and lack of functionalities of CO2–PCs limit the scope of their application in high value-added and functional materials. In this article, the first CO2-based polycarbonate with the ability to autonomously self-heal is constructed via a one-pot synthetic strategy. The key to the success of the synthetic strategy is efficient tandem three different catalytic reactions, i.e., hydrolysis of epoxides, immortal copolymerization of CO2/epoxides, and thiol–ene click reactions in a one-pot process. Based on the standard tensile testing, these CO2-based materials show robust self-healing properties, where the extensibility, maximal strength, and Young’s modulus of the specimens can almost entirely recover to their original value under ambient temperature. Our studies demonstrate that the self-heali...

Immortal copolymerization of epoxides/CO2 using macro-chain-transfer agent (macro-CTA) is a useful method to prepare CO2-based block copolymers for manufacturing high value-added materials. Despite a variety of CO2-based block copolymers that have been reported using distinct macro-CTAs, issues including catalytic activity and blocking efficiency for the immortal polymerization remain superficially understood. Here, we systematically studied the reaction activity and blocking efficiency by using various macro-CTAs (including PPG, PEG, and PS) in the presence of two classical catalyst systems ((BDI)ZnOAc and SalenCoTFA/PPN-TFA). By analysis of the gel permeation chromatograms via mathematical deconvolution, it comes to a conclusion that the size, nature, and ratio of [macro-CTA]/[Cat.] strongly influence the catalytic activity of the reaction and blocking efficiency for the resultant block copolymers. Thin film self-assembly of PS/PPC block copolymers was investigated, and the results were analyzed by SEM ...

Control over the orientation of cylindrical and lamellar domains is required for pattern transfer in block copolymer lithography. Previous work mainly focuses on the use of random copolymer brushes to control the wetting behaviors of block copolymers (BCPs), but random copolymerization is only limited to a few monomer pairs. Here we demonstrate the use of homopolymer brushes/mats to modify the substrate to form a chemically homogeneous surface. The surface affinity is tuned by changing the monomer substituent, and a variety of wetting behaviors are obtained in BCP films on homopolymer brushes/mats. Three series of hydroxy-terminated or cross-linkable homopolymers, including polymethacrylate, polyacrylate, and polystyrene derivatives, are prepared for controlling the BCP–substrate interaction. Both preferential and nonpreferential wetting behaviors of poly(styrene-b-methyl methacrylate), poly(styrene-b-rac-lactide), and poly(styrene-b-propylene carbonate) films are obtained as the homopolymer structures ch...

The addition of water as a chain transfer reagent during the copolymerization reaction of epoxides and carbon dioxide has been shown as a promising method for producing CO2-based polycarbonate polyols. These polyols can serve as drop-in replacements for petroleum derived polyols for polyurethane production or designer block copolymers. Ironically, during the history of CO2/epoxide coupling development, water was generally considered primarily as an aversion reagent. That is, in its presence, low catalytic activity and high polydispersity was normally observed. Recently, we reported a water-mediated tandem metal-coordination CO2/epoxide copolymerization and organobase catalyzed ring-opening polymerization (ROP) approach for the one-pot synthesis of an ABA CO2-based triblock copolymers. As in previous studies, water was deemed as the chain transfer reagent in this tandem strategy for producing CO2-based polyols. Herein is presented a mechanistic study aimed at determining the intimate role water plays durin...

Just add water: The copolymerization of propylene oxide and CO2 catalyzed by a cobalt complex is tolerant to the addition of water as chain-transfer reagent to afford polyols (HO-(PPC)-OH) with narrow molecular weight distributions (see picture; PPC=poly(propylene carbonate); PLA=polylactide). The addition of an organocatalyst to these polyols in the presence of lactides produces well-defined triblock copolymers (PLA-b-PPC-b-PLA).

As a cheap and easily obtainable raw material, epichlorohydrin is an attractive candidate for copolymerization with CO2 to produce degradable polycarbonate. However, the poor polymer selectivity as well as the concomitant production of ether linkage units in the previous studies hindered further research on this topic, such as asymmetric, stereo- and regioselective ring-opening of epichlorohydrin during its copolymerizaton with CO2. Herein, we report highly stereospecific alternating copolymerization of CO2 and epichlorohydrin for the first time by utilizing chiral bifunctional cobalt–salen catalysts. It was found that the substituents on the phenonate groups around the metal center had a notable effect on the regioselectivity of the ring-opening step for epichlorohydrin. Using an enantiopure salenCo(III) complex bearing an adamantane group and an appended bulky dicyclohexyl ionic ammonium salt, a highly regioregular ring-opening step was observed with a concomitant 97% retention of configuration at the m...

The use of carbon dioxide as a carbon source for the synthesis of organic chemicals can contribute to a more sustainable chemical industry. Because CO(2) is such a thermodynamically stable molecule, few effective catalysts are available to facilitate this transformation. Currently, the major industrial processes that convert CO(2) into viable products generate urea and hydroxybenzoic acid. One of the most promising new technologies for the use of this abundant, inexpensive, and nontoxic renewable resource is the alternating copolymerization of CO(2) and epoxides to provide biodegradable polycarbonates, which are highly valuable polymeric materials. Because this process often generates byproducts, such as polyether or ether linkages randomly dispersed within the polycarbonate chains and/or the more thermodynamically stable cyclic carbonates, the choice of catalyst is critical for selectively obtaining the expected product. In this Account, we outline our efforts to develop highly active Co(III)-based catalysts for the selective production of polycarbonates from the alternating copolymerization of CO(2) with epoxides. Binary systems consisting of simple (salen)Co(III)X and a nucleophilic cocatalyst exhibited high activity under mild conditions even at 0.1 MPa CO(2) pressure and afforded copolymers with99% carbonate linkages and a high regiochemical control (∼95% head-to-tail content). Discrete, one-component (salen)Co(III)X complexes bearing an appended quaternary ammonium salt or sterically hindered Lewis base showed excellent activity in the selectively alternating copolymerization of CO(2) with both aliphatic epoxides and cyclohexene oxide at high temperatures with low catalyst loading and/or low pressures of CO(2). Binary or one-component catalysts based on unsymmetric multichiral Co(III) complexes facilitated the efficient enantioselective copolymerization of CO(2) with epoxides, providing aliphatic polycarbonates with99% head-to-tail content. These systems were also very efficient in catalyzing the terpolymerization of cyclohexene oxide, propylene oxide and CO(2). The resulting terpolymer had a single glass-transition temperature and a single thermolysis peak. This Account also provides a thorough mechanistic understanding of the high activities, excellent selectivities, and unprecedented stereochemical control of these Co(III)-based catalysts in the production of CO(2) copolymers . The catalysis occurs through a cooperative monometallic mechanism, in which the Lewis acidic Co(III) ion serves as electrophile to activate then epoxide and the nucleophilic counterion or cocatalyst serves as a nucleophile to initiate polymer-chain growth. The high activity and excellent regioselectivity observed in the epoxide ring-opening reactions results from epoxide activation through the moderate electrophilicity of the Co(III) ion, the fast insertion of CO(2) into the Co-O bond, and the facile dissociation of the propagating carboxylate species from the central metal ion. The reversible intra- or intermolecular Co-O bond formation and dissociation helps to stabilize the active Co(III) species against reversion to the inactive Co(II) ion. We also describe our laboratory's recent preparation of the first crystalline CO(2)-based polymer via highly stereospecific copolymerization of CO(2) and meso-cyclohexene oxide and the selective synthesis of perfectly alternating polycarbonates from the coupling of CO(2) with epoxides bearing an electron-withdrawing group.

An example of crystalline CO2-based polymer from the asymmetric alternating copolymerization of CO2 and cyclohexene oxide is reported. Isotacticity of poly(cyclohexene carbonate) (PCHC) has the critical influence on the crystallinity, and only copolymers with a isotacticity of more than 90% are crystallizable. The stereoregular PCHC is a typical semi-crystalline thermoplastic, and possesses a high melting point (T m) of 215–230°C and a decomposition temperature of ca. 310°C. The spherulitic morphology of (R)-PCHC grows in a clockwise spiral from a center, and that of (S)-PCHC is a counterclockwise spiral, while the stereocomplex of (S)-PCHC/(R)-PCHC (1/1 mass ratio) presents lath-like dendritic crystal. The novel crystalline CO2-based polycarbonate represents a rare example of optically active polymers with unique crystallization behavior. Our findings reflect the critical influence of stereoregularity on the crystallization for this kind of polymeric materials, and may lead to developments of thermal-resistance CO2 copolymers for application in engineering thermoplastics.

A series of tridentate dianionic ligands [4-(t)Bu-6-R-2-(3-R'-5-(t)Bu-2-OC(6)H(2))N=CH C(6)H(2)O](2-) (L) [R = R' = (t)Bu (L1); R = CMe(2)Ph, R' = (t)Bu (L2); R = adamantyl, R' = (t)Bu (L3); R = R' = CMe(2)Ph (L4); R = SiMe(2)(t)Bu, R' = CMe(2)Ph (L5)] were synthesized. Reactions of TiCl(4) with 1 equiv of ligands L1-L5 in toluene afford five-coordinate titanium complexes with general formula LTiCl(2) [L = L1 (1); L2 (2); L3 (3); L4 (4); L5 (5)]. The addition of tetrahydrofuran (THF) to titanium complex 5 readily gives THF-solvated six-coordinate complex 6, which also was obtained by reaction of TiCl(4) with 1 equiv of ligand L5 in THF. Reactions of ZrCl(4) with 1 or 2 equiv of ligands L1-L5 afford six-coordinate zirconium mono(ligand) complexes LZrCl(2)(THF) [L = L2 (7); L4 (8); L5 (9)], and bis(ligand) complexes L(2)Zr [L = L1 (10); L4 (11)]. The molecular structures of complexes 2, 8, and 11 were established by single-crystal X-ray diffraction studies. Upon activation with methylaluminoxane, complexes 1-9 are active for ethylene polymerization. The activities and half-lifes of the catalyst systems based on zirconium complexes are more than 10(6) g of polyethylene (mol Zr)(-1) h(-1) and 6 h, respectively. Complex 9 is more active and long-lived, with a turnover frequency (TOF) of 2.6 × 10(5) (mol C(2)H(4)) (mol Zr)(-1) h(-1), a half-life of >16 h, and a total turnover number (TON) of more than 10(6) (mol C(2)H(4)) (mol Zr)(-1) at 20 °C and 0.5 MPa pressure. Even at 80 °C, complex 9/MAO catalyst system has a long lifetime (t(1/2) > 2 h), as well as high activity that is comparable with that at 20 °C. When activated with methylaluminoxane (MAO), complex 9 also show moderate catalytic activity and more than 99% 2,1-regioselectivity for 1-hexene oligomerization.

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 CO 2 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 sp 3 -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 CO 2 with chiral PO at various conditions.

A large amount of interesting information on the alternating copolymerization of CO2 with terminal epoxides has already been reported, such as the regiochemistry of epoxide ring-opening and the stereochemistry of the carbonate unit sequence in the polymer chain. Moreover, the microstructures of CO2 copolymers from propylene oxide and cyclohexene oxide have also been well-studied. However, the microstructure of the CO2 copolymer from styrene oxide (SO), an epoxide that contains an electron-withdrawing group, has not yet been investigated. Herein, we focus on the spectroscopic assignment of the CO2 copolymer from styrene oxide at the diad level by using three kinds of model dimer compounds, that is, T-T, H-T, and H-H. By comparing the signals in the carbonyl region, we concluded that the signals at δ=154.3, 153.8, and 153.3 ppm in the (13)C NMR spectrum of poly(styrene carbonate) were due to tail-to-tail, head-to-tail, and head-to-head carbonate linkages, respectively. Moreover, various isotactic and syndiotactic model compounds based on T-T, H-T, and H-H (dimers (R,R)-T-T, (S,S)-T-T, and (R,S)-T-T; (R,R)-H-T, (S,S)-H-T, and (R,S)-H-T; (R,R)-H-H, (S,S)-H-H, and (R,S)-H-H) were synthesized for the further spectroscopic assignment of stereospecific poly(styrene carbonate)s. We found that the carbonate carbon signals were sensitive towards the stereocenters on adjacent styrene oxide ring-opening units. These discoveries were found to be well-matched to the microstructures of the stereoregular poly(styrene carbonate)s that were prepared by using a multichiral Co(III)-based catalyst system.

Enantiopure metal-complex catalyzed asymmetric alternating copolymerization of CO(2) and meso-epoxides is a powerful synthetic strategy for preparing optically active polycarbonates with main-chain chirality. The previous studies regarding chiral zinc catalysts provided amorphous polycarbonates with moderate enantioselectivity, and thus, developing highly stereoregular catalysts for this enantioselective polymerization is highly desirable. Herein, we report the synthesis of highly isotactic poly(cyclohexene carbonate)s from meso-cyclohexene oxide using dissymmetrical enantiopure salenCo(III) complexes in conjunction with bis(triphenylphosphine)iminium chloride (PPNCl) as catalyst. The presence of a chiral induction agent such as (S)-propylene oxide or (S)-2-methyltetrahydrofuran significantly improved the enantioselectivity regarding (S,S)-salenCo(III) catalyst systems. Up to 98:2 of RR:SS was observed in the resultant polycarbonates obtained from the catalyst system based on (S,S)-salenCo(III) complex 4d bearing an adamantyl group on the phenolate ortho position, in the presence of (S)-2-methyltetrahydrofuran. Primary ONIOM (DFT:UFF) calculations, which were performed to investigate the effect of the competitive coordination of (S)-induction agent versus cyclohexene oxide to Co(III) center on enantioselectivity, suggest that the (S)-C-O bond in cyclohexene oxide is more favorable for cleavage, due to the interaction between oxygen atom of (S)-induction agent and (S)-C-H of the coordinated cyclohexene oxide. The highly isotactic poly(cyclohexene carbonate) is a typical semicrystalline polymer, possessing a melting point of 216 °C and a decomposition temperature of 310 °C.

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.

The kinetic resolution of racemic terminal epoxides with CO2 as reagent via enantioselective coupling represents an attractive method for affording enantiopure epoxides and optically active organic carbonates. A multichiral cobalt(III) complex in conjunction with an ammonium salt is an efficient catalyst system for the asymmetric coupling reaction of CO2 and racemic epoxides, and up to 97.1% ee for cyclic carbonate product and the highest krel (kinetic resolution coefficient) to date of 75.8 was obtained. The variation of nucleophilic co-catalyst and its relative loading dramatically changes the product selectivity and enantioselectivity. Both the anion and cation of ammonium salts have significant effects on the catalytic kinetic resolution process. An ammonium salt consisting of an anion with poor leaving ability and a bulky cation benefits for improving the enantioselectivity. The excess co-catalyst loading favors selective production of cyclic carbonate via the intramolecular cyclic elimination of the formed linear carbonate. A higher krel was observed in the excess co-catalyst loading, in comparison with one equivalent co-catalyst loading, predominantly resulting in polymer formation at the same temperature. It was also found that the excess co-catalyst loading led to significant increases in the regioselective ring-opening at the methylene carbon of various terminal epoxides, including styrene oxide with an electron-withdrawing group. The present study also offers a detailed mechanistic explanation of the role of the nucleophilic co-catalyst in the asymmetric coupling of racemic epoxides with CO2 using multichiral Co(III) complexes.