Copolymerization System Research Articles

Recent Advances in Nickel Catalysts with Industrial Exploitability for Copolymerization of Ethylene with Polar Monomers.

The direct copolymerization of ethylene with polar monomers to produce functional polyolefins continues to be highly appealing due to its simple operation process and controllable product microstructure. Low-cost nickel catalysts have been extensively utilized in academia for the synthesis of polar polyethylenes. However, the development of high-temperature copolymerization catalysts suitable for industrial production conditions remains a significant challenge. Classified by the resultant copolymers, this review provides a comprehensive summary of the research progress in nickel complex catalyzed ethylene-polar monomer copolymerization at elevated temperatures in the past five years. The polymerization results of ethylene-methyl acrylate copolymers, ethylene-tert-butyl acrylate copolymers, ethylene-other fundamental polar monomer copolymers, and ethylene-special polar monomer copolymers are thoroughly summarized. The involved nickel catalysts include the phosphine-phenolate type, bisphosphine-monoxide type, phosphine-carbonyl type, phosphine-benzenamine type, and the phosphine-enolate type. The effective modulation of catalytic activity, molecular weight, molecular weight distribution, melting point, and polar monomer incorporation ratio by these catalysts is concluded and discussed. It reveals that the optimization of the catalyst system is mainly achieved through the methods of catalyst structure rational design, extra additive introduction, and single-site catalyst heterogenization. As a result, some outstanding catalysts are capable of producing polar polyethylenes that closely resemble commercial products. To achieve industrialization, it is essential to further emphasize the fundamental science of high-temperature copolymerization systems and the application performance of resultant polar polyethylenes.

Copper Quantum Dot/Polyacrylamide Composite Nanospheres: Spreading on Quartz Flake Surfaces and Displacing Crude Oil in Microchannel Chips.

Polyacrylamide, silica, and other nanoparticles have all been realized in the field of enhanced oil recovery. Researchers often explore the mechanisms of spreading behavior and simulated displacement to develop more efficient types of nanoparticles. In this study, copper quantum dots were introduced into a acrylamide copolymerization system to obtain composite nanospheres and its structure, topographic, and application performance were characterized. The results show that the composite nanospheres have a particle size of around 25 nm, are uniformly loaded with copper particles, and have good temperature resistance. The spreading ability on the quartz flake surfaces and displacement effect in microchannels of composite nanospheres, acrylamide copolymer nanospheres, and copper quantum dots were compared by nanofluid spreading experiments and microchannel chip oil displacement experiments. The results indicate that the composite nanospheres can effectively reduce the water contact angle, promote the spreading of aqueous phase, and accelerate the oil droplet removal process; the accelerating effect is stronger than other samples. Its oil displacement effect is also the strongest, and it is minimized by the influence of channel size, temperature, and dispersing medium, with better stratigraphic adaptability. This work supports the practical application of copper quantum dot/polyacrylamide composite nanospheres in the oilfield.

Toward the production of block copolymers in microbial cells: achievements and perspectives.

The microbial production of polyhydroxyalkanoate (PHA) block copolymers has attracted research interests because they can be expected to exhibit excellent physical properties. Although post-polymerization conjugation and/or extension have been used for PHA block copolymer synthesis, the discovery of the first sequence-regulating PHA synthase, PhaCAR, enabled the direct synthesis of PHA-PHA type block copolymers in microbial cells. PhaCAR spontaneously synthesizes block copolymers from a mixture of substrates. To date, Escherichia coli and Ralstonia eutropha have been used as host strains, and therefore, sequence regulation is not a host-specific phenomenon. The monomer sequence greatly influences the physical properties of the polymer. For example, a random copolymer of 3-hydroxybutyrate and 2-hydroxybutyrate deforms plastically, while a block copolymer of approximately the same composition exhibits elastic deformation. The structure of the PHA block copolymer can be expanded by in vitro evolution of the sequence-regulating PHA synthase. An engineered variant of PhaCAR can synthesize poly(D-lactate) as a block copolymer component, which allows for greater flexibility in the molecular design of block copolymers. Therefore, creating sequence-regulating PHA synthases with a further broadened substrate range will expand the variety of properties of PHA materials. This review summarizes and discusses the sequence-regulating PHA synthase, analytical methods for verifying block sequence, properties of block copolymers, and mechanisms of sequence regulation. KEY POINTS: • Spontaneous monomer sequence regulation generates block copolymers • Poly(D-lactate) segment can be synthesized using a block copolymerization system • Block copolymers exhibit characteristic properties.

Preparation and Characterization of Acrylic and Methacrylic Phospholipid-Mimetic Polymer Hydrogels and Their Applications in Optical Tissue Clearing.

The 2-methacryloyloxyethyl phosphorylcholine (MPC) polymers are mimetic to phospholipids, being widely used as biocompatible polymers. In our previous study, MPC polymer hydrogels proved more effective for optical tissue clearing compared to acrylamide (AAm) polymer hydrogels. In the present study, 2-acryloyloxyethyl phosphorylcholine (APC) was synthesized and employed to create hydrogels for a comparative analysis with methacrylic MPC-based hydrogels. APC, an acrylic monomer, was copolymerized with AAm in a similar reactivity. In contrast, MPC, as a methacrylic monomer, demonstrated higher copolymerization reactivity than AAm, leading to a spontaneously delayed two-step polymerization behavior. This suggests that the polymer sequences and network structures became heterogeneous when both methacrylic and acrylic monomers, as well as crosslinkers, were present in the copolymerization system. The molecular weight of the APC polymers was considerably smaller than that of the MPC polymers due to the formation of mid-chain radicals and subsequent β-scission during polymerization. The swelling ratios in water and strain sweep profiles of hydrogels prepared using acrylic and methacrylic compounds differed from those of hydrogels prepared using only acrylic compounds. This implies that copolymerization reactivity influences the polymer network structures and crosslinking density in addition to the copolymer composition. APC-based hydrogels are effective for the optical clearing of tumor tissues and are applicable to both passive and electrophoretic methods.

Double crosslinking decellularized bovine pericardium of dialdehyde chondroitin sulfate and zwitterionic copolymer for bioprosthetic heart valves with enhanced antithrombogenic, anti-inflammatory and anti-calcification properties.

Due to the increasing aging population and the advancements in transcatheter aortic valve replacement (TAVR), the use of bioprosthetic heart valves (BHVs) in patients diagnosed with valvular disease has increased substantially. Commercially available glutaraldehyde (GA) cross-linked biological valves suffer from reduced durability due to a combination of factors, including the high cell toxicity of GA, subacute thrombus, inflammation and calcification. In this study, oxidized chondroitin sulfate (OCS), a natural polysaccharide derivative, was used to replace GA to cross-link decellularized bovine pericardium (DBP), carrying out the first crosslinking of DBP to obtain OCS-BP. Subsequently, the zwitterion radical copolymerization system was introduced in situ to perform double cross-linking to obtain double crosslinked BHVs with biomimetic modification (P(APM/MPC)-OCS-BP). P(APM/MPC)-OCS-BP presented enhanced mechanical properties, collagen stability and enzymatic degradation resistance due to double crosslinking. The ex vivo AV-shunt assay and coagulation factors test suggested that P(APM/MPC)-OCS-BP exhibited excellent anticoagulant and antithrombotic properties due to the introduction of P(APM/MPC). P(APM/MPC)-OCS-BP also showed good HUVEC-cytocompatibility due to the substantial reduction of its residual aldehyde group. The subcutaneous implantation also demonstrated that P(APM/MPC)-OCS-BP showed a weak inflammatory response due to the anti-inflammatory effect of OCS. Finally, in vivo and in vitro results revealed that P(APM/MPC)-OCS-BP exhibited an excellent anti-calcification property. In a word, this simple cooperative crosslinking strategy provides a novel solution to obtain BHVs with good mechanical properties, and HUVEC-cytocompatibility, anti-coagulation, anti-inflammatory and anti-calcification properties. It might be a promising alternative to GA-fixed BP and exhibited good prospects in clinical applications.

Model-Based design of a novel process applicable to solution and slurry polymerization with phase change

This work aims on developing a novel process that is applicable to solution and slurry polymerization, which can efficiently control production efficiency, product properties and reactor thermal load through changing the flow ratios of cooled evaporation streams between different reactors. Furthermore, various process routes can be created by varying the destinations of cooled evaporation streams, markedly enhancing the process flexibility. To provide a thorough insight into the characteristics of the developed process, numerical simulations based on coupling the constructed models of polymerization reaction kinetics, thermodynamic properties and reactors are conducted to comprehensively study the impact of various factors (e.g., process routes, pressure, monomer and catalyst concentration, flow rates of cooled evaporation streams in different reactors) on the ethylene/1-octene solution copolymerization system with several stirred reactors connected in series. Some strategies for regulating production efficiency, product properties and reactor heat load of different process routes are obtained.

Synthesis, kinetic study and characterization of C5‐dienes/styrene copolymers via living anionic polymerization in cyclopentyl methyl ether solvent

Abstract1,3‐Dienes/styrene sequence‐controlled copolymers are widely used as thermoplastic elastomers, transparent impact resin and synthetic rubber and other materials. In this work, the binary anionic copolymerization of styrene (S) and C5‐dienes including 1,3‐pentadiene (P, E/Z = 65/35) and isoprene (I) were studied in cyclopentyl methyl ether (CPME) ‘green’ solvent using n‐BuLi as initiator, and the effects of copolymerization monomer ratio and polar additive (PA) on the copolymerization kinetics and monomer sequence distributions were investigated. The kinetic analysis results showed that all copolymerization systems were the first‐order reaction and the C5‐dienes/S could be quantitatively consumed. The addition of S or I was conducive to the efficient conversion of P. Although the addition of PAs had little effect on the polymerization rate, it had a great influence on the microstructure and sequence distribution of the copolymer. 1H NMR tracking analysis showed that, for S/P copolymerization with different feeding ratios 1/3 < fP < 2/3, the instant composition FP in the copolymer remained relatively constant at 15% < FP < 35% when the monomer conversion rate was below 60%, and thus the inevitable formation of P microblocks in subsequent polymerization sequences was observed. Additionally, similar sequence distributions were obtained in the case of I/P copolymerization systems. By contrast, S/I copolymerization conformed to the typical random copolymerization pattern, and the copolymerization activity of S was slightly higher than that of the I in CPME. The use of strong PAs such as 2,2‐di(2‐tetrahydrofuran)propane directly resulted in a change of monomer sequence from a random pattern to a gradual block pattern. Moreover, the 3,4‐isoprene branch units were much more sensitive to solvent and PA than 1,2‐pentadiene units for C5‐dienes; also Fourier transform infrared and DSC analysis verified the microstructure and sequence analysis results mentioned above. In addition, the results of gel permeation chromatography showed that the copolymerization process in CPME had excellent controllable characteristics. © 2023 Society of Industrial Chemistry.

Sequence design in terpolymerization of ε-caprolactone, CO2 and cyclohexane oxide: Random ester-carbonate distributions lead to large-span tunability

It is of great interest to make a degradable material widely tailorable to replace petroleum-derived products among diverse applications. Here, we report the construction of a new multi-purpose degradable material for the first time via a simple ternary copolymerization system comprising ε-caprolactone (ε-CL), cyclohexane oxide (CHO) and CO2. Under low pressure of 1 bar ∼5 bar, the ring-opening polymerization (ROP) of ε-CL and ring-opening copolymerization (ROCOP) of CO2 and CHO can simultaneously proceed. The carbonate units are randomly distributed on the polymer chain. These random terpolymers have controllable molar mass (10–106 kDa) and compositions (4–33 mol% CO2). And the obtained materials show large-span tunability from tough plastic to elastomer and even adhesive.

Multinuclear Zinc-Magnesium Hydroxide Carboxylates: A Predesigned Model System for Copolymerization of CO2 with Epoxides.

Among numerous catalysts in the ring-opening copolymerization of epoxides with carbon dioxide (CO2), zinc dicarboxylate complexes are the most common type, and in the family of metal-based homogeneous catalysts, zinc and magnesium complexes have attracted widespread attention. We report on the synthesis and structural characterization of a zinc-magnesium benzoate framework templated by the central hydroxide anion with μ3-κ2:κ2:κ2 coordination mode, [ZnMg2(μ3-OH)(O2CPh)5]n (n = 1 or 2). The resulting heterometallic system forms stable Lewis acid-base adducts with tetrahydrofuran (THF) and cyclohexene oxide (CHO), which crystallize as the hexanuclear zinc-magnesium hydroxide carboxylate cluster [ZnMg2(μ3-OH)(O2CPh)5(L)2]2 (L = THF or CHO). Their X-ray crystal structure analysis revealed that the Zn center prefers 4-fold coordination and the Mg centers demonstrated the ability to accommodate higher coordination numbers, and as a result, the heterocyclic molecules are exclusively bonded to 6-fold Mg atoms. The heteronuclear carboxylate aggregates appeared active in the copolymerization reaction at elevated temperatures to produce an alternating poly(cyclohexene carbonate).

In Situ Copolymerization Studies of Lignin, Acrylamide, and Diallyldimethylammonium Chloride: Mechanism, Kinetics, and Rheology.

In this work, free-radical polymerization of kraft lignin, acrylamide (AM), and diallyldimethylammonium chloride (DADMAC) was studied in detail. In situ nuclear magnetic resonance (NMR), rheological analysis, and particle size techniques were conducted to understand the physicochemical characteristics of this copolymerization system. The copolymerization of lignin-AM and lignin-DADMAC had activation energies of 65.7 and 69.3 kJ/mol, respectively, and followed the first-order kinetic model, which was monitored by in situ H1 NMR results. The highest conversions of AM and DADMAC were 96 and 68%, respectively, in the copolymerization of lignin, AM, and DADMAC at the molar ratio of 5.5:2.4:1, pH 2 and 85 °C. The results illustrated that the participation of AM in the reaction was essential for polymerizing DADMAC to lignin due to less steric hindrance of AM than DADMAC facilitating its bridging performance. The monomer conversion ratio and dynamic rheology of the reaction system indicated that lignin acted as an inhibitor in the copolymerization reaction. The particle size analysis of the reaction mixtures reflected the alteration in the size of particles from coarse particles (>300 μm) to fine particles (<10 and 10-50 μm) and suspension to colloidal systems when the reaction progressed. The oscillation study of the reaction media confirmed the gradual increase in the viscosity of the reaction media, illustrating the crosslinking of lignin, AM, and DADMAC.

Mechanistic aspect for the atom transfer radical polymerization of itaconimide monomers with methyl methacrylate: a computational study

Abstract Atom transfer radical polymerization (ATRP) is a versatile &amp; famous technique for the synthesis of well defined molecular architectures. In ATRP, there is a dynamic equilibrium exists between active &amp; dormant species. Therefore, ATRP progress through a sequence of activation &amp; deactivation cycles, ending upon complete monomer consumption &amp; termination reactions are minimized. This paper presents a systematic computational study on kinetics &amp; thermodynamics associates in the ATRP of itaconimide monomers &amp; methyl methacrylate (MMA). For this, the copolymerization system is modeled as a unimer, dimer &amp; trimer of various itaconimides &amp; MMA monomer. The density functional theory with B3LYP functional &amp; 6–31 + G(d)/LanL2DZ basis sets is used in the prediction of geometries &amp; energetics associated with the dissociation of terminal R–X bond present in the unimer, dimer &amp; trimer. The relative equilibrium constant (K ATRP) for the ATRP activation/deactivation steps is calculated from the free energy values associated with dissociation of R–X bond. The relative K ATRP values of dimer &amp; trimer of selected monomers is compared with their respective unimer. From the transition state geometries of the dimeric propagating radical, activation energy is calculated. The gas phase rate coefficients for propagation (k p) (of itaconimides &amp; MMA copolymerization) are calculated using the standard transition state theory. The effect of system parameters such as solvent, temperature &amp; substituent on K ATRP &amp; k p values of dimer is investigated systematically. The change in the initiating system &amp; temperature has significant effect on k p values as compared to solvent &amp; various substituent. The K ATRP values of dimer &amp; trimer dormant species are higher as compared to their respective monomeric species. The neighboring monomer &amp; penultimate monomer plays vital role in kinetics &amp; thermodynamics associated with copolymerization. The obtained initial results show that the mechanism of copolymerization of itaconimide monomers &amp; MMA follows penultimate model.

Ring-opening copolymerization of CO2 with epoxides catalyzed by binary catalysts containing half salen aluminum compounds and quaternary phosphonium salt

The synthesis and characterization of two different categories of Al(III) compounds supported by unsymmetrical phenoxy-imine ligands with furan-2-ylmethanimine and thiophen-2-ylmethanimine side arms is described. Reactions of the ligands with Al(CH3)3 in a 1:1 and 2:1 stoichiometric ratio resulted in the formation of the corresponding monosubstituted and disubstituted Al(III) compounds in quantitative yields. These compounds were fully characterized using various spectroscopic techniques and elemental analysis. Single-crystal X-ray diffraction studies revealed that the Al(III) center in the monosubstituted compounds adopt a distorted tetrahedral geometry while those in the disubstituted compounds adopt a distorted trigonal bipyramidal geometry with a geometric index τ = 0.72. These compounds along with tetraphenylphosphonium chloride (TPPCl) form a binary catalyst system for the ring-opening copolymerization (ROCOP) of CO2 with cyclohexene oxide (CHO) and propylene oxide (PO). They show notable activity producing alternating polycarbonate with TOF up to 107 h−1 and high selectivity (carbonate linkages > 80%). The catalytic activities of the compounds have been investigated by varying the substituent in the phenolate core and in the imine backbone.

Increasing the Hydrophilicity of Cyclic Ketene Acetals Improves the Hydrolytic Degradation of Vinyl Copolymers and the Interaction of Glycopolymer Nanoparticles with Lectins.

Radical ring-opening polymerization (rROP) of cyclic ketene acetals (CKAs) with traditional vinyl monomers allows the synthesis of degradable vinyl copolymers. However, since the most commonly used CKAs are hydrophobic, most degradable vinyl copolymers reported so far degrade very slowly by hydrolysis under physiological conditions (phosphate-buffered saline, pH 7.4, 37 °C), which can be detrimental for biomedical applications. Herein, to design advanced vinyl copolymers by rROP with high CKA content and enhanced degradation profiles, we reported the copolymerization of 2-methylene-1,3,6-trioxocane (MTC) as a CKA with vinyl ether (VE) or maleimide (MI) derivatives. By performing a point-by-point comparison between the MTC/VE and MTC/MI copolymerization systems, and their counterparts based on 2-methylene-1,3-dioxepane (MDO) and 5,6-benzo-2-methylene-1,3-dioxepane (BMDO), we showed negligible impact on the macromolecular characteristics and similar reactivity ratios, suggesting successful substitution of MDO and BMDO by MTC. Interestingly, owing to the hydrophilicity of MTC, the obtained copolymers exhibited a faster hydrolytic degradation under both accelerated and physiological conditions. We then prepared MTC-based glycopolymers, which were formulated into surfactant-free nanoparticles, exhibiting excellent colloidal stability up to 4 months and complete degradation under enzymatic conditions. Importantly, MTC-based glyconanoparticles also showed a similar cytocompatibility toward two healthy cell lines and a much stronger lectin affinity than MDO-based glyconanoparticles.

Composition Regulation by Flow Copolymerization of Methyl Methacrylate and Glycidyl Methacrylate with Free Radical Method

AbstractIt is important to match the feeding ratio of comonomers to the composition ratio in the resulting copolymers as closely as possible in industrial production, where the goal is often to produce more a homogeneous composition in copolymers. In this study, a flow copolymerization system with a conventionally initiated free radical method, together with randomly selected polymerization conditions is investigated. It is succeeded in achieving a closer match between the composition ratio and feeding ratio than previously reported in the copolymerization of styrene with methyl methacrylate and of glycidyl methacrylate with methyl methacrylate, which will widen the range of applications, by precisely controlling the mixing and heating in a flow polymerization apparatus. This is confirmed by the fact that the estimated values of reactivity ratios, r1 and r2, which are used in the reaction kinetics of copolymerization, are close to 1.

New sustainable Mannich-functionalized lignin flocculants for ultra-efficiently tailoring wastewater purification

The complex pollutants in wastewater, especially the highly toxic and carcinogenic azo-dyes, seriously endanger the water ecosystem and human health. Using renewable lignin to develop efficient flocculants is of great significance to environmental sustainability. Nevertheless, the preparation process of lignin-based flocculant is not only inefficient and cumbersome, but also brings serious pollution, making their development unsustainable. In this study, a new type of ultra-efficient Mannich-functionalized lignin-based flocculants was prepared by a simple, green strategy. Lignin-based flocculants were synthesized by copolymerizing lignin with acrylamide in a UV-induced aqueous copolymerization system and then modified by Mannich with formaldehyde and diethylenetriamine. Comprehensive considering the influence of molecular weight, charge density and amphiphilicity, herein, two different types of lignin-based flocculant (LBF1 and LBF2) could be precisely tuned by adjusting the dose of formaldehyde and diethylenetriamine. The results showed that the turbidity removal rate of LBF1 for kaolin suspension could be up to 99.31%, and the decolorization rate of Acid Black 1, Direct Red 80 and Reactive Red 2 solutions using LBF2 was more than 99.60%, which outperformed almost all other lignin-based flocculants reported in the previous reports. Moreover, LBF1 and LBF2 showed excellent resistance to the complex external environment, reflecting their outstanding universality.

Degradable Polystyrene via the Cleavable Comonomer Approach

Polystyrene (PS) is a major commodity polymer widely used in various applications ranging from packaging to insulation thanks to its low cost, high stiffness, and transparency as well as its relatively high softening temperature. Similarly to all polymers prepared by radical polymerization, PS is constituted of a C–C backbone and thus is not degradable. To confer degradability to such materials, the copolymerization of vinyl monomers with a cyclic monomer that could undergo radical ring-opening is an efficient method to introduce purposely cleavable bonds into the polymer backbone. Dibenzo[c,e]-oxepane-5-thione (DOT) is a cyclic thionolactone monomer known for its efficient copolymerization with acrylate derivatives but so far could not be incorporated into PS backbones. From a theoretical study combining density functional theory (DFT) and kinetic models using the PREDICI software, we showed that the modification of experimental conditions could overcome these limitations and that high molar mass degradable polystyrene (Mw close to 150 000 g·mol–1) could be prepared via statistical insertion of thioester groups into the polymer backbone. This copolymerization process is compatible with conventional free radical polymerization and reversible deactivation radical polymerization (RDRP) techniques such as nitroxide mediated polymerization (NMP). Thanks to favorable reactivity ratios allowing only a few mol % of thioester units to be randomly incorporated, there was no major modification of the thermal and mechanical properties of the PS. The degradation of such PS could be performed in tetrahydrofuran (THF) at room temperature (RT) in 1 h using 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) as a base, leading to oligomers with Mn close to 2000 g·mol–1. We successfully demonstrate further applicability of these copolymerization systems for the phototriggered decomposition of PS in solution as well as the synthesis of cross-linked PS networks degradable into soluble side products.

Propylene polymerization and copolymerization with polar monomers facilitated by flexible cycloalkyl substituents in α-diimine systems

The aryl substituents as well as backbones in the α-diimine catalysts have a significant influence on the olefin (co)polymerization. In this work, the effect of the cycloalkyl and dibenzhydryl substituents as well as backbones of the α-diimine Pd(II) catalysts on the propylene polymerization and copolymerization has been explored. The Pd(II) catalysts led to the moderate activities (level of 104 g mol−1 h−1), tunable molecular weights (5.6–125.2 kg/mol) and highly branched (155–249/1000C) polypropylene during homopolymerization. Among the catalysts, the catalyst Pd3 with the cyclopentyl substituents and dimethyl backbone resulted in the highest molecular weight and activity in the propylene polymerization. Moreover, during the copolymerization of polypropylene-MA, the Pd(II) catalysts showed low activities and yielded low to moderate molecular weight (Mn up to 39.8 kg/mol) polar functionalized copolymers with high branching density (134–217/1000C) and tunable incorporation ratios (1.0–11.5 mol%). Overall, the catalyst Pd3 was also observed to be optimal for the copolymerization reaction, owing to the excellent copolymerization ability of propylene with MA and some other acrylic derived monomers. Further, the rigid substituents with a high steric hindrance played an unfavorable role during the (co)polymerization, which was contrary to the ethylene polymerization. In summary, compared with the rigid bulky dibenzhydryl substituents, the cyclopentyl substituents not only endowed the propylene homopolymerization system with the highest molecular weight and activity, but also provided the copolymerization system with the highest activity, incorporation ratio, and molecular weight. In addition, the incorporation of polar functionalized units could notably change the surface properties of the polypropylene materials in this work.

Customized Utilization Strategies of Industrial Lignin to Produce Adsorbents and Flocculants Based on Fractionation and Adequate Structural Interpretation.

Lignin, a by-product of pulping and biorefinery, has great potential to replace petrochemical resources for wastewater purification. However, the defects of lignin, such as severe heterogeneity, inferior reactivity and poor solubility, characterize the production process of lignin-based products by high energy consumption and serious pollution. In this study, several lignin fractions with relatively homogeneous structure were first obtained by organic solvent fractionation, and their structures were fully deciphered by various characterization techniques. Subsequently, each lignin component was custom-valued for wastewater purification based on their structural characteristics. Benefiting from the high reactivity and reaction accessibility, the lignin fraction (lignin-1) refined by dissolving in ethanol and n-butanol could been used as a raw material to produce cationic lignin-based flocculant (LBF) in a copolymerization system using green, cheap and recyclable ethanol as solvent. The lignin fraction (lignin-2) extracted by methanol and dioxane showed low reactivity and high carbon content, which was used to produce lignin-based activated carbon (LAC) with phosphoric acid as activator. Moreover, the influences of synthetic factors on the purification capacity were discussed, and the LBF and LAC produced under the optimal conditions showed distinguished purification effect on kaolin suspension and heavy metal wastewater, respectively. Furthermore, the corresponding purification mechanism and external factors were also elaborated. It is believed that this cleaner production strategy is helpful for the valorization of lignin in wastewater resources.

Vinyl copolymers with faster hydrolytic degradation than aliphatic polyesters and tunable upper critical solution temperatures

Vinyl polymers are the focus of intensive research due to their ease of synthesis and the possibility of making well-defined, functional materials. However, their non-degradability leads to environmental problems and limits their use in biomedical applications, allowing aliphatic polyesters to still be considered as the gold standards. Radical ring-opening polymerization of cyclic ketene acetals is considered the most promising approach to impart degradability to vinyl polymers. However, these materials still exhibit poor hydrolytic degradation and thus cannot yet compete with traditional polyesters. Here we show that a simple copolymerization system based on acrylamide and cyclic ketene acetals leads to well-defined and cytocompatible copolymers with faster hydrolytic degradation than that of polylactide and poly(lactide-co-glycolide). Moreover, by changing the nature of the cyclic ketene acetal, the copolymers can be either water-soluble or can exhibit tunable upper critical solution temperatures relevant for mild hyperthermia-triggered drug release. Amphiphilic diblock copolymers deriving from this system can also be formulated into degradable, thermosensitive nanoparticles by an all-water nanoprecipitation process.

A scalable and simple lignin-based polymer for ultra-efficient flocculation and sterilization

Current flocculation and sterilization are two separate steps that can cause environmental and economic problems. Lignin, an inedible industrial by-product, as raw material to prepare polymer that simultaneously realize flocculation and sterilization is of great significance for carbon neutral, sewage recycling, and economic benefit. However, the inherent defects of lignin such as heterogeneity, poor solubility and low reactivity cause difficulty in preparing and applying lignin-based polymers. Under this context, an energy-saving synergistic technology incorporating lignin refining and photoinitiated biphasic copolymerization system was pioneered, and an ultra-efficient dual-function lignin-based polymer with hyperbranched amphiphilic structure was successfully prepared, which contributed to 99.6% removal rate and distinguished sterilization effect for E. coli suspension at an ultra-low dose (4 mg/L and 10 mg/L, respectively). The purification mechanism indicated that the first flocculation was attributed to the synergy of charge attraction, bridging and sweeping, while the subsequent sterilization was achieved by blocking the metabolism and changing membrane permeability. The examination on various external influencing factors showed great adaptability of this lignin-based polymer to complex sewage environment with superiority over existing commercial products.