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ConspectusElectron-deficient boron-based catalysts with metal-free but metallomimetic characteristics provide a versatile platform for chemical transformations. However, their catalytic performance is usually lower than that of the corresponding metal-based catalysts. Furthermore, many elaborate organoboron compounds are produced via time-consuming multistep syntheses with low yields, presenting a formidable challenge for large-scale applications of these catalysts. Given this context, the development of organoboron catalysts with the combined advantages of high efficiency and easy preparation is of critical importance.Therefore, we envisioned that the construction of a dynamic Lewis multicore system (DLMCS) by integrating the Lewis acidic boron center(s) and a Lewis basic ammonium salt in one molecule would be particularly efficient for on-demand applications because of the intramolecular synergistic effect. This Account summarizes our recent efforts in developing modular organoboron catalysts with unprecedented activities for several chemical transformations. A series of mono-, di-, tri-, and tetranuclear organoboron catalysts was readily designed and prepared in nearly quantitative yields over two steps using commercially available feedstocks. Notably, these catalysts can be modularly tailored by fine control over the electrophilic property of the Lewis acidic boron center(s), electronic and steric effects of the electropositive ammonium cation, linker length between the boron center and the ammonium cation, the number of boron centers, and the nucleophilic anion. This modular design allows systematic manipulation of the reactivity and efficacy of the catalysts, thus optimizing suitable catalysts for versatile chemical transformations. These include the coupling of CO2 and epoxides, copolymerization of CO2 and epoxides, ring-opening polymerization (ROP) of epoxides, and ring-opening copolymerization (ROCOP) of epoxides and cyclic anhydrides.The utilization of mononuclear organoboron catalysts provided a turnover frequency of 11050 h-1 for the CO2/propylene oxide coupling reaction, an unprecedented efficiency of 5.0 kg of polymer/g of catalyst for the copolymerization of CO2 and cyclohexene oxide, and a record-breaking catalytic efficiency of 7.4 kg of polymer/g of catalyst for the ROCOP of epoxides with cyclic anhydrides. A turnover number of 56500 was observed at a catalyst loading of 10 ppm for the ROP of epoxides using the dinuclear catalysts. The tetranuclear organoboron catalysts realized the previously intractable task of the copolymerization of CO2 and epichlorohydrin, producing poly(chloropropylene carbonate) with the highest molecular weight of 36.5 kg/mol reported to date.Furthermore, the study revealed that the interaction between the dynamic Lewis multicore, that is, the intramolecular synergistic effect between the boron center(s) and the quaternary ammonium salt, plays a key role in mediating the catalytic activity and selectivity. This was based on investigations of the crystal structures of the catalysts, key intermediates, reaction kinetics, and density functional theory calculations. The modular tactics for the construction of organoboron catalysts presented in this Account should inspire more advanced catalyst designs.

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 (

The copolymerization of carbon dioxide (CO2) and epoxides to produce aliphatic polycarbonates is a burgeoning technology for the large-scale utilization of CO2 and degradable polymeric materials. Even with the wealth of advancements achieved over the past 50 years on this green technology, many challenges remain, including the use of metal-containing catalysts for polymerization, the removal of the chromatic metal residue after polymerization, and the limited practicable epoxides, especially for those containing electron-withdrawing groups. Herein, we provide kinds of pinwheel-shaped tetranuclear organoboron catalysts for epichlorohydrin/CO2 copolymerization with >99% polymer selectivity and quantitative CO2 uptake (>99% carbonate linkages) under mild conditions (25-40 °C, 25 bar of CO2). The produced poly(chloropropylene carbonate) has the highest molecular weight of 36.5 kg/mol and glass transition temperature of 45.4 °C reported to date. The energy difference (ΔEa = 60.7 kJ/mol) between the cyclic carbonate and polycarbonate sheds light on the robust performance of our metal-free catalyst. Control experiments and density functional theory (DFT) calculations revealed a cyclically sequential copolymerization mechanism. The metal-free feature, high catalytic performance under mild conditions, and no trouble with chromaticity for the produced polymers imply that our catalysts are practical candidates to advance the CO2-based polycarbonates.

A series of highly active organoboron catalysts for the coupling of CO2 and epoxides with the advantages of scalable preparation, thermostability, and recyclability is reported. The metal-free catalysts show high reactivity towards a wide scope of cyclic carbonates (14 examples) and can withstand a high temperature up to 150 °C. Compared with the current metal-free catalytic systems that use mol % catalyst loading, the catalytic capacity of the catalyst described herein can be enhanced by three orders of magnitude (epoxide/cat.=200 000/1, mole ratio) in the presence of a cocatalyst. This feature greatly narrows the gap between metal-free catalysts and state-of-the-art metallic systems. An intramolecular cooperative mechanism is proposed and certified on the basis of investigations on crystal structures, structure-performance relationships, kinetic studies, and key reaction intermediates.

The utilization of carbon dioxide (CO2) as a monomer for copolymerization with three-membered cyclic ethers, also known as oxiranes or epoxides, has received much renewed interest due to the need for degradable polymeric materials derived from renewable resources. Since the early discovery of the catalytic coupling of CO2 and oxiranes to afford polycarbonates, the area has progressed significantly over the 50 succeeding years. Herein, we describe the currently well-established catalyzed copolymerization process of oxiranes and carbon dioxide utilizing homogeneous metal catalysts. Pertinent to the commercial success of this process is the presence of rapid and reversible chain-transfer reactions that occur in the presence of protic impurities or additives leading to the formation of macropolyols. The focus of this review is to summarize the various synthetic strategies for the production of designer block copolymers for various applications in material science and biomedicine.

This manuscript describes a kind of bifunctional organocatalyst with unprecedented reactivity for the synthesis of polyethers via ring-opening polymerization (ROP) of epoxides under mild conditions. The bifunctional catalyst incorporates two 9-borabicyclo[3.3.1]nonane centers on the two ends as Lewis acidic sites for epoxide activation and a quaternary ammonium halide in the middle as the initiating site. The catalyst could be easily prepared in two steps from commercially available stocks on up to kilogram scale with ≈100 % yield. The organoboron catalyst mediated ROP of epoxides displays living behavior with low catalyst loading (5 ppm) and enables the synthesis of polyethers with molecular weights of over a million grams per mole (>106  g mol-1 ). Based on the investigations on crystal structure of catalyst, MALDI-TOF, and 11 B NMR spectroscopy, an intramolecular ammonium cation assisted SN 2 mechanism is proposed and verified by DFT calculations.

The metallic catalyst-dominated alternating copolymerization of CO2 and epoxides has flourished for 50 years; however, the involved multistep preparation of the catalysts and the necessity to remov...

The impact of thermal history on the kinetic response of thin thermoresponsive diblock copolymer poly(diethylene glycol monomethyl ether methacrylate)-block-poly(poly(ethylene glycol) methyl ether methacrylate), abbreviated as PMEO2MA-b-POEGMA300, films is investigated by in situ neutron reflectivity. The PMEO2MA and POEGMA300 blocks are both thermoresponsive polymers with a lower critical solution temperature. Their transition temperatures (TTs) are around 25 °C (TT1, PMEO2MA) and 60 °C (TT2, POEGMA300). Thus, by applying different temperature protocols (20 to 60 or 20 to 40 to 60 °C), the PMEO2MA-b-POEGMA300 thin films experience different thermal histories: the first protocol directly switches from a swollen to a collapsed state, whereas the second one switches first from a swollen to a semicollapsed and finally to a collapsed state. Although the applied thermal histories differ, the response and final state of the collapsed films are very close to each other. After the thermal stimulus, both films present a complicated response composed of an initial shrinkage, followed by a rearrangement. Interestingly, a subsequent reswelling of the collapsed film is only observed in the case of having applied a thermal stimulus of 20 to 40 °C. The normalized film thickness and the D2O amount of each layer in the PMEO2MA-b-POEGMA300 films are consistent at the end of the two different thermal stimuli. Hence, it can be concluded that the thermal history does not influence the final state of the PMEO2MA-b-POEGMA300 films upon heating. Based on this property, these thin films are especially suitable for the temperature switches on the nanoscale, which may experience different thermal histories.

The linear shrinkage behavior in thermoresponsive diblock copolymer films and its potential application in temperature sensors are investigated. The copolymer is composed of two thermoresponsive blocks with different transition temperatures (TTs): di(ethylene glycol) methyl ether methacrylate (MEO2MA; TT1 = 25 °C) and poly(ethylene glycol) methyl ether methacrylate (OEGMA300; TT2 = 60 °C) with a molar ratio of 1:1. Aqueous solutions of PMEO2MA-b-POEGMA300 show a three-stage transition upon heating as seen with optical transmittance and small-angle X-ray scattering: dissolution (T TT2). Due to the restrictions in the polymer chain arrangement introduced by the solid Si substrate, spin-coated PMEO2MA-b-POEGMA300 films exhibit an entirely different internal structure and transition behavior. Neutron reflectivity shows the absence of an ordered structure normal to the Si substrate in as-prepared PMEO2MA-b-POEGMA300 films. After exposure to D2O vapor for 3 h and then increasing the temperature above its TT1 and TT2, the ordered structure is still not observed. Only a D2O enrichment layer is formed close to the hydrophilic Si substrate. Such PMEO2MA-b-POEGMA300 films show a linear shrinkage between TT1 and TT2 in a D2O vapor atmosphere. This special behavior can be attributed to the synergistic effect between the restrained collapse of the PMEO2MA blocks by the still swollen POEGMA300 blocks and the impedance of chain arrangement by the Si substrate. Based on this unique behavior, spin-coated PMEO2MA-b-POEGMA300 films are further prepared into a temperature sensor by implementing Ag electrodes. Its resistance decreases linearly with temperature between TT1 and TT2.

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...

Producing polyesters with high molecular weight (Mn ) through ring-opening copolymerization (ROCOP) of epoxides with cyclic anhydrides remains a major challenge. Herein, we communicate a metal-free, highly active, and high thermoresistance system for the ROCOP of epoxides with cyclic anhydrides to prepare polyesters (13 examples). The organoboron catalysts can endure a reaction temperature as high as 180 °C for the ROCOP of cyclohexane oxide (CHO) with phthalic anhydride (PA) without the observation of any side reactions. The average Mn of the produced poly(CHO-alt-PA) climbed to 94.5 kDa with low polydispersity (Ð=1.19). Furthermore, an unprecedented turnover number of 9900, equivalent to an efficiency of 7.4 kg of polyester/g of catalyst, was achieved at a feed ratio of CHO/PA/catalyst=20000:10000:1 at 150 °C. Kinetic studies, crystal structure analysis, 11 B NMR spectra, and DFT calculations provided mechanistic justification for the effectiveness of the catalyst system.

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.

Microphase separated block copolymer electrolyte (BCE) systems are attractive candidates for electrochemical systems because the concentrated ionic groups in one block provide pathways for facile ion transport while the non-ionic block bestows mechanical integrity and suppresses excess water uptake. Numerous researchers have prepared and studied bulk BCEs as ion conductors, but the inherent complex nature and imprecise architecture of these materials make it difficult to extract definitive conclusions on how the macromolecular structure influences ion transport. In this work, the process of block copolymer lithography was demonstrated to create model nano-confined polymer electrolyte brushes that mimic lamellae structures found in bulk BCE membranes. Both nano-confined anion and cation conducting polymer brushes were prepared and excellent ionic conductivities (10−2 S cm−1 to 10−1 S cm−1) were obtained. Surprisingly, the nano-confined polycation and polyanion brushes displayed similar, or in some instances lower, in-plane electrical resistance values to the non-confined samples and shrinkage upon introduction of ionic charges. Using 2D force mapping AFM and atomistic molecular dynamics simulations, it was inferred that the nano-confined polymer electrolytes were less susceptible to counterion condensation explaining the unexpected changes in brush thickness after introduction of ionic moieties and the relatively low electrical resistance values. Overall, the block copolymer lithography platform presented in this work enables fabrication of precisely defined BCEs to systematically investigate how the microstructure and confinement governs counterion condensation and ion transport.

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...

Bioinspired polyphenol/polyamine codeposition has been demonstrated by the competence for surface modification; however, the reaction processes including mechanism and kinetics remain superficially understood. In this work, the catechol (CA)-amine reaction has been thoroughly investigated by using CA and two amines m-phenylenediamine and piperazine. We verify that both primary and secondary amines are prone to link with CA through Michael addition to form polyphenol/polyamine oligomers under aerobic and mild-alkaline conditions. Molecular simulations indicate that the Michael addition products are dominant for both aromatic and aliphatic amines with CA, which supports the durable chem- and phystability of the codeposited coatings. The aggregation kinetics of polyphenol/polyamine is provided for the first time, and the formed aggregates show high-adhesive properties, which can be deposited as the skin layers for high-performance nanofiltration membranes.

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...

Porous separators are key components for lithium-ion batteries (LIBs) and they have drawn considerable attention because of their vital role in governing battery cost and performance (e.g., power density, safety, and longevity). Here, zirconia-coated separators were fabricated via a facile biomineralization process with the aim to improve the performance of commercialized polypropylene separators. The as-prepared organic-inorganic composite separators show excellent thermal stability, even at the melting temperature (160 °C) of polypropylene. This is due to the well-distributed zirconia coatings on the separator surfaces. Furthermore, the interfacial impedance of the composite separators is only 343.8 Ω, which is four times lower than the pristine polypropylene ones. The results demonstrate an attractive method to prepare organic-inorganic composite separators with outstanding properties, which makes them promising candidates for high-performance LIBs.

A Janus membrane with opposing wettability was first reported with both function of water-to-oil and oil-to-water emulsification. This membrane is conveniently fabricated by single-surface deposition of polydopamine/polyethylenimine (PDA/PEI). The asymmetric wettability can also reduce the transmembrane resistance during the process, indicating an economical and promising strategy to prepare various emulsions. This research opens a novel avenue for exploring and understanding the Janus membrane, and provides a perspective to design the asymmetric membrane structures with promoted performance in conventional membrane processes.

Directed self-assembly (DSA) of block copolymers (BCPs) combines advantages of conventional photolithography and polymeric materials and shows competence in semiconductors and data storage applications. Driven by the more integrated, much smaller and higher performance of the electronics, however, the industry standard polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA) in DSA strategy cannot meet the rapid development of lithography technology because its intrinsic limited Flory–Huggins interaction parameter (χ). Despite hundreds of block copolymers have been developed, these BCPs systems are usually subject to a trade-off between high χ and thermal treatment, resulting in incompatibility with the current nanomanufacturing fab processes. Here we discover that polystyrene-b-poly(propylene carbonate) (PS-b-PPC) is well qualified to fill key positions on DSA strategy for the next-generation lithography. The estimated χ-value for PS-b-PPC is 0.079, that is, two times greater than PS-b-PMMA (χ = 0.029 at ...

Enhanced capabilities of stain removal and comfort control are simultaneously achieved by the light and thermo dual-responsive copolymer poly(triethylene glycol methyl ether methacrylate- co-ethylene glycol methacrylate- co-acrylamide azobenzene) (P(MEO3MA- co-EGMA- co-AAAB)) cross-linked on cotton fabrics. P(MEO3MA- co-EGMA- co-AAAB) is synthesized by sequential atom transfer radical polymerization with a molar ratio of 8 (MEO3MA):1 (EGMA):1 (AAAB). The MEO3MA units induce a thermoresponsive behavior to the copolymer. The hydrophilicity of the copolymer films can be further improved by the light-induced trans- cis isomerization of the AAAB units with UV radiation. The copolymer is facilely immobilized onto cotton fabrics with 1,2,3,4-butane tetracarboxylic acid as cross-linker. Due to the immobilization of P(MEO3MA- co-EGMA- co-AAAB), the hydrophilicity of the fabric surface is increased under UV radiation. Therefore, by simply installing a UV light source in the washing machine, better capability of stain removal is realized for the cross-linked cotton fabrics. It can prominently reduce the consumption of energy, water, and surfactants in laundry. In addition, the trans-AAAB units of the copolymer cause the cross-linked P(MEO3MA- co-EGMA- co-AAAB) layer to be more hydrophobic under ambient conditions. Hence, the copolymer can more easily collapse and form a porous structure on the fabrics. Thus, the air permeability of cotton fabrics cross-linked with P(MEO3MA- co-EGMA- co-AAAB) is enhanced by 13% at human body temperature as compared to P(MEO3MA- co-EGMA), giving improved comfort control during daily wear.

Homoporous membranes fabricated by self-assembled block copolymers (BCPs) have gained growing attention for their easy availability of well-ordered nanostructures for precise separation. However, it remains a challenges to improve the mechanical integrity, hydrophilic properties, and pore functionalities of the existing systems. To this end, we report an organic-mineral composite hybrid nanoporous BCP membrane with attractive superhydrophilicity, mechanical stability, and fouling-resistance derived from a bioinspired block copolymer, poly(propylene carbonate)- block-poly(4-vinylcatechol acetonide) (PPC- b-PVCA). The key advances include the following. (1) The PPC minor block is qualified as sacrificial domain because of its alkali sensitivity for generating monodisperse nanopores. (2) The PVCA matrix block contains the catechol groups, which enables the formation of inorganic layer via a biomineralization process, thus producing an organic-mineral composite nanoporous BCP membrane with attractive superhydrophilicity, mechanical stability, and fouling resistance. A ∼200 nm thickness BCP film with monodisperse through-pores of 12 nm diameter cylinders oriented perpendicularly to a supporting microfiltration membrane is fabricated by sequential blade-casting, solvent annealing, hydrolysis sacrificial block, and biomineralization process. The mechanical stability, high water flow (114 L m

Single ion conducting polymer electrolyte membranes (PEMs) are found at the heart of many electrochemical devices (e.g., fuel cells, flow batteries, electrolyzers, electrodialysis, etc.).(1) The key requirements for such materials include high ionic conductivity, electron insulation, mechanical resilience, selectivity (i.e., high transference #), and chemical, thermal, and mechanical stability.(2, 3) Ionic conductivity is particularly important because it strongly influences the ohmic overpotential in the said electrochemical devices affecting device efficiency.(1, 4) Block copolymer electrolytes represent an attractive set of PEM materials because their micro-phase architecture yields greater ion conduction over their random copolymer counterparts.(5-7) Furthermore, the block copolymer charateristic gives rise to a variety of morphological architectures, while engineering of the block copolymer’s self-assembly influences domain alignment.(8-12) However, there is lack of systematic studies correlating molecular level structural design to bulk material properties like ion transport. In this work, a model lamellae-forming diblock copolymer electrolyte system was manipulated to examine the extent of ion domain connectivity on ion conduction.(13, 14) Careful control of the model system’s volume fraction gave diblock copolymer structures with slightly rich electrolyte domains or slightly rich hydrophobic domains. The slightly rich electrolyte domains had greater contiguous area fraction while simultaneously demonstrating fewer terminal defects. Having a contiguous area fraction from 0.95 to 1.0 resulted in a 2x improvement in ionic conductivity over a non-micro-phase separated block copolymer electrolyte or a micro-phase separated block copolymer electrolyte with poor connectivity. Incremental adjustment in the extent of connectivity revealed an exponential growth curve for ion conductivity as a function of contiguous area fraction. Furthermore, the benefits that a micro-phase separated block copolymer electrolyte affords in terms of ion conductivity were not realized when the block copolymer electrolyte had poor connectivity. The results of this work have far reaching implication into the rationale design of PEM materials based upon block copolymer designs. This talk will emphasize the importance of maximizing ion domain connectivity while taking great strides to minimize terminal defects to boost ion transport in PEM materials. This talk will close with future directions on how molecular level engineering of block copolymer electrolytes offer the potential to reveal how other structural features (e.g., tortuosity(15), grain boundaries(5), and counterion condensation) alter ion transport in PEM materials(16, 17). 1. H. Strathmann et al., Ion-Exchange Membranes in the Chemical Process Industry. Industrial & Engineering Chemistry Research 52, 10364-10379 (2013). 2. H. Strathmann, Ion-Exchange Membrane Separation Processes, Volume 9. Membrane Science and Technology (Elsevier Science, Amsterdam, The Netherlands, 2004), vol. 9. 3. T. Sata, Ion Exchange Membranes: Preparation, Characterization, Modification and Application. (Royal Society of Chemistry, Cambridge, UK, 2004). 4. A. Z. Weber, J. Newman, Modeling Transport in Polymer-Electrolyte Fuel Cells. Chemical Reviews 104, 4679-4726 (2004). 5. Y. A. Elabd, M. A. Hickner, Block Copolymers for Fuel Cells. Macromolecules 44, 1-11 (2011). 6. N. Li, M. D. Guiver, Ion Transport by Nanochannels in Ion-Containing Aromatic Copolymers. Macromolecules 47, 2175-2198 (2014). 7. Y. Schneider et al., Ionic Conduction in Nanostructured Membranes Based on Polymerized Protic Ionic Liquids. Macromolecules 46, 1543-1548 (2013). 8. H. Hu, M. Gopinadhan, C. O. Osuji, Directed self-assembly of block copolymers: a tutorial review of strategies for enabling nanotechnology with soft matter. Soft Matter 10, 3867-3889 (2014). 9. M. Luo, T. H. Epps, III, Directed Block Copolymer Thin Film Self-Assembly: Emerging Trends in Nanopattern Fabrication. Macromolecules 46, 7567-7579 (2013). 10. S. Ji, L. Wan, C.-C. Liu, P. F. Nealey, Directed self-assembly of block copolymers on chemical patterns: A platform for nanofabrication. Progress in Polymer Science, 54-55, 76-127 (2016). 11. S.-J. Jeong et al., Directed self-assembly of block copolymers for next generation nanolithography. Materials Today 16, 468-476 (2013). 12. M. P. Stoykovich, P. F. Nealey, Block copolymers and conventional lithography. Materials Today 9, 20-29 (2006). 13. I. P. Campbell, G. J. Lau, J. L. Feaver, M. P. Stoykovich, Network Connectivity and Long-Range Continuity of Lamellar Morphologies in Block Copolymer Thin Films. Macromolecules 45, 1587-1594 (2012). 14. C. G. Arges, Y. Kambe, H. S. Suh, L. E. Ocola, P. F. Nealey, Perpendicularly Aligned, Anion Conducting Nanochannels in Block Copolymer Electrolyte Films. Chemistry of Materials 28, 1377-1389 (2016). 15. X. Feng et al., Scalable Fabrication of Polymer Membranes with Vertically Aligned 1 nm Pores by Magnetic Field Directed Self-Assembly. ACS Nano 8, 11977-11986 (2014). 16. K. M. Beers, D. T. Hallinan, X. Wang, J. A. Pople, N. P. Balsara, Counterion Condensation in Nafion. Macromolecules 44, 8866-8870 (2011). 17. K. M. Beers, N. P. Balsara, Design of Cluster-free Polymer Electrolyte Membranes and Implications on Proton Conductivity. ACS Macro Letters 1, 1155-1160 (2012). Figure 1

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.

Uniform bulk graft modification of vinyl monomers to polypropylene or polyethylene membranes was achieved by combining gamma (γ)-ray pre-irradiation-induced graft copolymerization and supercritical carbon dioxide (scCO 2 )-swelling polymerization techniques. In the first step, the polymer membranes were irradiated with γ-rays originated from cobalt-60 resource under oxygen or air atmosphere at ambient temperature, and thus potential active sites, hydroperoxides and diperoxides, were uniformly formed on the polymer backbone. Then, graft copolymerization of vinyl monomers such as styrene, N -vinylpyrrolidone ( N -VP), methyl methacrylate (MMA) and 2-hydroxyethyl methacrylate (HEMA) impregnated into polymer substrates with the aid of scCO 2 was initiated thermally within the host polymer by the polymer radicals (PO ) resulting from the decomposition of peroxides uniformly distributed in the irradiated polymer samples. The process parameters were controlled by the properties of the fluid phase (CO 2 /monomer mixture) and experimental conditions, such as monomer concentration, temperature and time. The bulk graft modification of polyolefin membranes was confirmed by element analysis, spectroscopy and microscopy.

Control over nanopore size and 3D structure is necessary to advance membrane performance in ubiquitous separation devices. Here, inorganic nanoporous membranes are fabricated by combining the assembly of cylinder-forming poly(styrene-block-methyl methacrylate) (PS-b-PMMA) block copolymer and sequential infiltration synthesis (SIS). A key advance relates to the use of PMMA majority block copolymer films and the optimization of thermal annealing temperature and substrate chemistry to achieve through-film vertical PS cylinders. The resulting morphology allows for direct fabrication of nanoporous AlOx by selective growth of Al2O3 in the PMMA matrix during the SIS process, followed by polymer removal using oxygen plasma. Control over the pore diameter is achieved by varying the number of Al2O3 growth cycles, leading to pore size reduction from 21 to 16 nm. 3D characterization, using scanning transmission electron microscopy tomography, reveals that the AlOx channels are continuous through the film and have a gradual increase in pore size with depth. Finally, the ultrafiltration performance of the fabricated AlOx membrane for protein separation as a function of protein size and charge is demonstrated.

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.

Selective transformation of carbon dioxide and epoxides into degradable polycarbonates (CO(2)-based copolymer) has been regarded as a most promising green polymerization process. Although tremendous progress has been made during the past decade, very few successful examples have been reported to synthesize well-defined block copolymers to expand the scope of these green copolymers. Herein, we report a tandem strategy combining two living polymerization techniques, salenCo(III)X-catalyzed styrene oxide SO/CO(2) copolymerization and ring-opening polymerization of lactide with DBU (1,8-diazabicyclo[5.4.0]undec-7-ene), for the synthesis of poly(styrene carbonate-block-lactide) copolymers. The key to the success of this tandem strategy is the judicious choice of water as the chain transfer and/or chain terminator reagent, which is added at the end of the salenCo(III)X-catalyzed SO/CO(2) copolymerization to in situ generate hydroxyl groups at the end of the polymer chains. The resulting polycarbonates with -OH end groups can thus be directly used as macroinitiators to subsequently initiate ring-opening polymerization of lactide to synthesize the diblock copolymers. Because of the living polymerization nature of both steps in this tandem strategy, we have demonstrated that the diblock copolymers synthesized possess well-defined structures with narrow molecular weight distributions and controllable lengths of both styrene carbonate and lactide blocks.

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.

A detailed study of the difference in reactivity of the copolymerization reactions of styrene oxidevs.propylene oxide with carbon dioxide utilizing binary (salen)cobalt(III) catalyst systems to provide perfectly alternating copolymers is reported. This investigation focuses on the discrepancy exhibited by these two terminal epoxides for the preference for C–O bond cleavage during the ring-opening process. It was found that the nucleophilic ring-opening of styrene oxide occurs predominantly at the methine Cα–O bond which leads to an inversion of configuration at the methine carbon center. This tendency results in a significantly lower reactivity as well as a deterrent for synthesizing stereoregular poly(styrene carbonate) when compared to the propylene oxide/CO2 process. The chiral environment about the metal center had a notable effect on the regioselectivity of the ring-opening step for styrene oxide, with the methylene Cβ–O bond being preferentially cleaved. Using a binary catalyst system composed of an unsymmetrical (S,S,S)-salenCo(III) complex in conjunction with the onium salt PPNY (PPN = bis(triphenylphosphine)iminium, and Y = 2,4-dinitrophenoxy), a highly regioregular ring-opening step was observed with a concomitant 96% retention of configuration at the methine carbon center.