Surface and Interface Engineering for Advanced Nanofiltration Membranes

Nanofiltration has been attracting great attention in alleviating the global water crisis because of its high efficiency,mild operation,and strong adaptability.Over decades,it remains a challenge to break the upper limit of performance and establish the formation-structureproperty relationship for nanofiltration membranes.This feature article summarizes our recent progress in the preparation of high-performance thin-film composite(TFC)nanofiltration membranes,focusing on the mussel-inspired deposition method and the optimized interfacial polymerization(IP).By accelerating the oxidation of polydopamine and equilibrating the rate of aggregation and deposition processes,the mussel-inspired deposition method realizes the rapid and uniform formation of selective coatings or nanofilms.Diverse deposition systems endow the selective layer with rich chemical structures and easy post-functionalization,highlighting its potential in water treatment.As for optimizing the conventional IP,the rapid polycondensation of amine and acid chloride groups is slowed down to enable the controllability of IP at the water-organic interface.The homogeneity and integrity of the TFC membranes are improved by constructing a uniform reaction platform and introducing a viscous medium to control the amine diffusion,which facilitates the water permeability and promotes the separation efficiency.We have proposed a series of practical strategies for improving TFC membranes and might provide more inspiration for other nanofiltration techniques.     

高分子化学线型缩聚反应数均聚合度计算的教学体验和改进

对高分子化学课程本科教学中有关线型缩聚反应数均聚合度的计算,以及聚合度与官能团过量之间的定性及定量关系进行了讨论。针对现有教学方法易引发学生误解和混淆的情况,定义了新的参数和发展了相应改进的计算方程。新的计算方程的计算过程清晰、参数定义明确、易于学生理解掌握,在实践中取得了良好的教学效果。     

Polyamide Nanofiltration Membrane from Surfactant-assembly Regulated Interfacial Polymerization of 2-Methylpiperazine for Divalent Cations Removal

Removal of metal ions from water can not only alleviate the scaling problem of domestic and industrial water, but also solve the water safety problem caused by heavy metal ion pollution. Here, we fabricate a positively charged nanofiltration membrane via surfactant-assembly regulated interfacial polymerization(SARIP) of 2-methylpiperazine(MPIP) and trimesoyl chloride(TMC). Due to the existence of methyl substituent, MPIP has lower reactive activity than piperazine(PIP) but stronger affinity to hexane, resulting in a nanofiltration(NF) membrane with an opposite surface charge and a loose polyamide active layer. Interestingly, with the help of sodium dodecyl sulfate(SDS) assembly at the water/hexane, the reactivity between MPIP and TMC was obviously increased and caused in turn the formation of a positively charged polyamide active layer with a smaller pore size, as well as with a narrower pore size distribution. The resulting membrane shows a highly efficient removal of divalent cations from water, of which the rejections of MgCl₂, CoCl₂ and NiCl₂ are higher than 98.8%, 98.0% and 98.0%, respectively, which are better than those of most of other positively charged NF membranes reported in literatures.     

基于“透过表面接枝”方式制备低分散性和高接枝密度聚合物刷的研究

"透过表面接枝"(grafting-through)是一种聚合物表面改性的新方法,可以显著改善传统grafting-from和grafting-to方法接枝工艺的缺陷,获得兼具高接枝密度和低分散性的聚合物刷产物.本文采用布朗动力学模拟方法,模拟研究了grafting-through方法接枝聚合物刷过程中的主控因素,从微观动力学角度阐明其特有的链增长趋同化效应是保持产物聚合物刷较低分散性的主因.引发效率在grafting-through中可显著提高,且产物聚合物刷的分子量呈现泊松分布.此外,反应中保持高的单体通量,可以同时实现产物聚合物较长的平均链长和较低的分散性,有利于制备性能优异的改性材料.该研究对深入理解grafting-through接枝过程的动力学主控因素,促进grafting-through技术的推广和工艺的改进具有一定的理论指导意义.     

Branched plasticizers derived from eugenol via green polymerization for low/non-migration and externally/internally plasticized polyvinyl chloride materials

The synthesis of nontoxic plasticizers derived from the waste residues of the rosin-processing industry can reduce pollution and promote the high-value utilization of the waste residues of rosin. In this study, four kinds of sustainable branched plasticizers derived from a biomass resource, eugenol (derived from the waste residues of the rosin processing industry), were synthesized via one-pot solvent free polymerization and used to plasticize polyvinyl chloride (PVC). Internally plasticized PVC was fabricated using thiolated DPE (branched plasticizers based on eugenol). The thermal stability, tensile properties, microstructure, volatility behavior, and solvent extraction resistance of plasticized PVC were investigated. Compared with the behavior of the commercial plasticizer dioctyl phthalate, the thermal stability, plasticizing efficiency, and migration resistance of the branched plasticizers are superior. The acute oral toxicity dose of each branched plasticizer was extremely high at 5000 mg/kg of body weight, with no deaths among test animals. Compared with externally plasticized PVC, the internally plasticized PVC showed zero weight loss in volatility and leaching tests despite its less effective plasticization. All the branched plasticizers have potential application in plastic products.     

Effective strategy for polymer synthesis: multicomponent reactions and click polymerization

The rational selection of organic reactions in polymer synthesis is an important research content of polymer science. In recent years, multicomponent reaction as an efficient and green synthesis method has attracted the wide attention of researchers, injecting new and powerful vitality into the field of polymer synthesis. In the study of multicomponent reaction, researchers found the intersection of multicomponent reaction and click chemistry and put forward the concept of Multicomponent Click Reaction (MCR-Click), which is a kind of Multicomponent Reaction with high activity, atomic economy, and some green chemical properties. The application of MCR in polymer chemistry is reviewed in this paper. It is expected that this reaction will arouse the attention of polymer chemists and play a new role in polymer science.     

Multiarm Star-Shaped Polydimethylsiloxanes with a Dendritic Branching Center

New multiarm stars have been synthesized based on polylithium derivatives of high-generation carbosilane dendrimers. In the synthesis of multiarm stars based on the eighth-generation dendrimer, steric hindrances were observed even during the synthesis of a polylithium initiator. Subsequently, this led to chain transfer reactions between growing arms, as well as other side effects. As a result, dense nanogel formations with a higher tendency of ordering than in classical objects of this type were isolated from the reaction mixture. The study of the rheology of multiarm stars based on sixth-generation dendrimers made it possible to determine the activation energies of viscous flow in these objects, which makes it possible to consider them as objects with a macromolecular nature and a reptation flow mechanism.     

Copolymeric nano/microgels of N-isopropylacrylamide and carboxyalkyl methacrylamides: Effect of methylene chains and the ionization state of the weak acids on size and sensitivity to pH and temperature

ABSTRACT

We prepared nano/microgels by precipitation copolymerization of N-isopropylacrylamide (NIPAAm), and one of three different carboxyalkyl methacrylamides [methacryloylamido hexanoic acid (M₅), 8-methacryloylamido octanoic acid (M₇), and 11-methacryloylamido undecanoic acid (M₁₀)], either in the acid forms or as carboxylates (potassium salts). The hydrodynamic diameter (Dh) of the nano/microgels prepared with the carboxylates was smaller (≈100 nm for M₁₀ copolymers), compared to the size of homopolymeric NIPAAm microgels prepared by dispersion polymerization (around 600 nm), indicating that the carboxylates act as surfactants reducing the size of the seeds during the polymerization process. These materials presented a swollen-shrunken transition temperature (T _tr) similar to the T _tr of the homopolymeric NIPAAm microgels, without pH sensitivity. On the other hand, the copolymeric microgels prepared from the acid form of the comonomers have a similar or bigger size than NIPAAm microgels. For these copolymers, the T _tr can be tuned by the type and proportion of acid comonomer used and present pH sensitivity. This is important for biomedical applications such as positive temperature control release. Polyelectrolyte titration demonstrates that the nano/microgels prepared with the carboxylates behave as hard spheres, while the microgels prepared with the weak acid behave as porous materials.     

基于聚合诱导自组装制备二氧化硅/聚合物纳米复合材料

纳米二氧化硅(SiO₂)颗粒以其高硬度、高比表面积、高稳定、价格合理等优势被广泛应用于复合材料的制备中,获得的SiO₂/聚合物复合材料通常具有优良的机械性能、很好的热稳定性以及增强的光学和电性能。近年来,随着聚合诱导自组装(PISA)的提出与发展,研究者们基于PISA发展了多种制备不同形貌聚合物纳米粒子的简便方法,为制备SiO₂/聚合物复合材料提供了新的思路。作者调研了近十年来基于PISA制备SiO₂/聚合物复合材料的相关研究,按照SiO₂与聚合物的结合作用和复合机理的不同,创新性地将SiO₂/聚合物复合材料的制备分为物理包封法、化学接枝法、超分子作用法和原位生长法。本综述重点论述复合材料的合成方法、主要性能及用途,同时分析各种复合方法的优缺点并对制备方法的未来发展做出展望,以期为相关领域科研工作者提供更清晰的脉络和更丰富的启示。     

Rate constant measurements for initial addition reactions of radicals at the propagation step of photo‐polymerization as studied by pulsed EPR spectroscopy

Pulsed EPR spectroscopy was employed to determine reaction rate constants at an early stage of addition reactions in radical polymerizations triggered by four initiator radicals, which were generated by photodissociation of four parent molecules. Two monomers (tert‐butylacrylate and tert‐butylmethacrylate) were examined as reactant. Stern–Volmer analysis on the measured decay time of electron spin echo intensity of reacting radicals provides rate constants for addition reactions. We focused on rate constants for the second step reaction between monomer and adduct radical that is produced by the first step addition reaction between initiator radical and monomer. The rate constant measured by pulsed EPR was evaluated by theoretical calculations in the light of (1) enthalpy difference between product radical and reactants and (2) charge transfer interaction between reacting radical and monomer. Copyright © 2016 John Wiley & Sons, Ltd.