Synthesis and characterization of silica nanoparticles with well-defined thermoresponsive PNIPAM via a combination of RAFT and click chemistry

Covalent functionalization of azide-modified SiO(2) with well-defined, alkyne-terminated poly(N-isopropylacrylamide) was accomplished by the Cu(I)-catalyzed [3 + 2] Huisgen cycloaddition. The alkyne-terminated RAFT chain transfer agent was first synthesized, and then the alkyne-terminated thermoresponsive poly(N-isopropylacrylamide) (PNIPAM) with different molecular weights were synthesized by the RAFT of NIPAM monomer. The polymerization kinetics and the evolution of number-average molecular weights (M(n)), and polydispersities (M(w)/M(n)), with monomer conversions were investigated. A copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) "grafting to" method was used to attach thermoresponsive polymers onto the exterior surface of SiO(2) nanoparticles which produced relatively high grafting density. The as-synthesized hybrid nanoparticles showed thermoresponsive behavior and were characterized by FTIR, XPS, TGA, DLS, and TEM, etc.     

利用原子转移自由基反应在超大孔聚苯乙烯微球表面接枝含糖聚合物刷

超大孔聚苯乙烯微球具有力学强度高、化学稳定性好、传质速率快等优点,但其表面疏水性强,无法衍生,要想用作生物大分子分离介质必须对其亲水改性。文中利用原子转移自由基(ATRP)反应的方法在超大孔聚苯乙烯微球(PS)表面原位接枝含糖聚合物刷,得到亲水改性的超大孔聚苯乙烯微球。对溶剂、配体、催化剂及温度等反应条件进行了详细考察,优化了接枝反应条件。含糖聚合物刷最大接枝量达到490.8 mg/g干球,改性后微球表面接触角由124°下降到42°,对蛋白的吸附量也降低了10.2倍,亲水性和生物相容性明显提高,同时微球的超大孔未被堵塞,且柔性含糖聚合物刷在后期衍生过程中还起到了"间隔臂"的作用,将是一种非常优良的生物大分子分离介质,在快流速蛋白分离色谱领域有很大应用潜力。     

Synthesis and characterization of water-soluble multiwalled carbon nanotubes grafted by a thermoresponsive polymer

Water-soluble multiwalled carbon nanotubes (MWNTs) with temperature-responsive shells were successfully prepared by grafting poly (N-isopropylacrylamide) (PNIPAM) from the sidewalls of MWNTs, via surface reversible addition-fragmentation chain transfer (RAFT) polymerization using RAFT agent functionalized MWNTs as the chain transfer agent. Thermogravimetric analysis (TGA) measurements showed that the weight composition of the as-grown PNIPAM polymers on the MWNTs can be well controlled by the feed ratio (in weight) of NIPAM to RAFT agent functionalized MWNTs (MWNT-SC(S)Ph). The MWNT-g-PNIPAM has good solubility in water, chloroform, and tetrahydrofuran (THF). Transmission electron microscope (TEM) and scanning electron microscope (SEM) images also showed that the MWNT-g-PNIPAM was dispersed individually and eventually bonded with the polymer layer by surface RAFT polymerization. The PNIPAM shell is very sensitive to a change of temperature. This method could find potential applications by grafting other functional polymer chains onto MWNTs.     

Controlling the Number of Arms of Polymer Stars with a Fullerene C60 Core

Abstract

Pure di‐ and tetra‐adducts can be obtained by grafting polystyrene (PS) chains onto C₆₀ via an atom transfer radical addition. Stars with a C₆₀ core and exactly six PS arms of molar mass ranging from 1000 to several 100,000 are easily produced by adding an excess of PSLi to the fullerene. Tri‐ to penta‐adducts can be prepared by controlling the stoichiometry PSLi/C₆₀. The number of grafts on the fullerene can be extended to seven or eight by initiation of the anionic polymerization of an adequate monomer with a “living” hexa‐adduct or by grafting onto this latter an halogen terminated polymer.     

大分子链转移剂活性对聚合物分散液晶电光性能的影响

采用可逆加成-断裂链转移(RAFT)、引发转移终止(Iniferter)、反向原子转移自由基聚合(RATRP)等活性自由基聚合方法,合成了分子量相近而带有不同端基的大分子链转移剂。通过紫外光聚合诱导相分离法制备聚合物分散液晶(PDLC)膜。通过研究大分子链转移剂光引发活性,发现采用RAFT聚合制备的大分子链转移剂具有较高的光活性,带有Iniferter活性基团的大分子链转移剂光活性很低。对不同大分子链转移剂制备的PDLC膜的电光性能进行比较,发现采用RAFT法合成的具有高光活性的大分子链转移剂能够使PDLC膜具有较高的开态透光率和较低的驱动电压。加入大分子链转移剂会导致PDLC记忆效应升高。     

Surface functionalization of biomaterials by radical polymerization

One effective strategy in the field of biomaterials is to develop biomimetic interfaces to modulate the cell behavior and promote tissue regeneration and surface modification is the best way to obtain biomaterial surfaces with the desired biological functions and properties. Surface radical polymerization offers many advantages compared to other methods, for instance, low cost and simplicity, ability to control the surface chemistry without changing the properties of the bulk materials by introducing high-density graft chains and precisely controlling the location of the chains grafted to the surface, as well as long-term chemical stability of the chains introduced by this method due to the covalent bonding. Because of the precise control of the macromolecules and easy preparation, controlled/living radical polymerization has been widely used to modify biomaterials. There are three main techniques: atom transfer radical polymerization (ATRP), nitroxide-mediated polymerization (NMP), and reversible radical addition-fragmentation chain transfer (RAFT) polymerization. Some other grafting methods such as plasma-induced polymerization, irradiation-induced polymerization, and photo-induced polymerization also have great potential pertaining to functionalization of biomaterials and tailoring of surface chemistry. This paper summarizes recent advances in the various grafting polymerization methods to enhance the surface properties and biological functions of biomaterials.     

RAFT聚合技术在无皂乳液聚合中的应用进展

在无皂乳液聚合体系中,通过使用两亲性RAFT试剂可以解决传统RAFT乳液聚合乳液稳定性差、分子量不可控和分子量分布宽等问题。从聚合特点、成核机理以及常用的两亲性RAFT试剂等方面总结了RAFT无皂乳液聚合技术的研究现状。两亲性RAFT试剂作用下的无皂乳液聚合符合RAFT活性聚合的一般特征。两亲性RAFT试剂浓度在其CMC值以上时主要通过胶束成核机理成核,在其CMC值以下则按均相成核机理成核的几率增大。常用的两亲性RAFT试剂主要是双硫酯或三硫酯。目前该方法已经成功应用于均聚物和嵌段共聚物的制备,今后可用于制备梯度共聚物等更多精细结构的聚合物。     

功能性聚丙烯酰胺类微球的制备及应用

介绍了功能性聚丙烯酰胺类微球的各种制备方法,主要为分散聚合法和无皂乳液聚合法。其中重点介绍了改进的无皂乳液聚合法-超声波无皂乳液聚合法、紫外光引发无皂乳液聚合法和微波加热无皂乳液聚合法;同时,还介绍了功能性聚丙烯酰胺类微球的种类和应用,诸如:温敏性聚丙烯酰胺微球、磁性聚丙烯酰胺微球、pH值响应聚丙烯酰胺类微球以及聚丙烯酰胺与无机微粒形成的复合微球。并对功能性聚丙烯酰胺类微球研究作了展望。     

RAFT聚合方法在碳纳米管表面接枝嵌段共聚物

首先在碳纳米管表面接上可用做RAFT聚合的链转移剂——二硫代碳酸酯,然后用这些管壁接有二硫代碳酸酯的碳纳米管作为链转移剂引发甲基丙烯酸甲酯和苯乙烯单体进行可控的嵌段聚合反应,首次报道了采用二步加料方式在碳纳米管的管壁上接枝上嵌段共聚物链。对嵌段共聚物的结构进行了红外光谱(FT-IR)、热重分析(TGA)、透射电镜(TEM)表征。     

China’s hydropower energy system toward carbon neutrality

Wind and solar powers will gradually become dominant energies toward carbon neutrality. Large-scale renewable energies, with strong stochasticity, high volatility, and unadjustable features, have great impacts on the safe operation of power system. Thus, an advanced hydropower energy system serving multiple energies is required to respond to volatility, with expanding role from a “stable energy supplier” to a “flexible efficiency regulator”. Future research and application can be considered from three aspects: 1) system expansion (e.g., the construction of large-scale hydropower/renewable energy bases in China, the construction of transnational hydropower energy internet, and the functional transformation of traditional hydropower reservoirs and generating units); 2) efficiency promotion (e.g., advanced intelligent forecasting, multi-objective operation, and risk management methods); and 3) supporting measures (e.g., market reform, benefit compensation and policy mechanism, technical standards, and laws and regulations).     

碳纳米管表面的RAFT接枝共聚物

首先在碳纳米管表面接枝上可用做RAFT聚合的链转移剂——二硫代碳酸酯,然后用管壁接枝有二硫代碳酸酯的碳纳米管作为链转移剂引发甲基丙烯酸甲酯(MMA)和苯乙烯(St)进行可控的自由基共聚合反应,从而在碳纳米管的管壁接枝上MMA和St共聚物,通过接枝共聚极大地提高了碳纳米管在有机溶剂中的分散性能。并对接枝共聚物的结构进行了较详细的表征。     

Thermo‐Switchable Materials Prepared Using the OEGMA‐Platform

We describe here the advantages of oligo(ethylene glycol)‐based (co)polymers for preparing thermoresponsive materials as diverse as polymer‐enzyme bio‐hybrids, injectable hydrogels, capsules for drug‐release, modified magnetic particles for in vivo utilization, cell‐culture substrates, antibacterial surfaces, or stationary phases for bioseparation. Oligo(ethylene glycol) methacrylates (OEGMAs) can be (co)polymerized using versatile and widely‐applicable methods of polymerization such as atom transfer radical polymerization (ATRP) of reversible addition‐fragmentation chain‐transfer (RAFT) polymerization. Thus, the molecular structure and therefore the stimuli‐responsive properties of these polymers can be precisely controlled. Moreover, these stimuli‐responsive macromolecules can be easily attached to–or directly grown from–organic, inorganic or biological materials. As a consequence, the OEGMA synthetic platform is today a popular option for materials design. The present research news summaries the progress of the last two years.     

Automated Optical‐Tweezers Assembly of Engineered Microgranular Crystals

In this work, a scalable automated approach for fabricating 3D microgranular crystals consisting of desired arrangements of microspheres using holographic optical tweezers and two‐photon polymerization is introduced. The ability to position microspheres as desired within lattices of any configuration allows designers to engineer the behavior of new metamaterials that enable advanced applications (e.g., armor that mitigates or redirects shock waves, acoustic lens for underwater imaging, damage detection, and noninvasive surgery, acoustic cloaking, and photonic crystals). Currently, no self‐assembly or automated approaches exist with the flexibility necessary to place specific microspheres at specific locations within a crystal. Moreover, most pick‐and‐place approaches require the manual assembly of spheres one by one and thus do not achieve the speed and precision required to repeatably fabricate practical volumes of engineered crystals. In this paper, the rapid assembly of 4.86 µm diameter silica spheres within differently packed 3D crystal‐lattice examples of unprecedented size using fully automated optical tweezers is demonstrated. The optical tweezers independently and simultaneously assemble batches of spheres that are dispensed to the build site via an automated syringe pump where the spheres are then joined together within previously unattainable patterns by curing regions of photocurable prepolymer between each sphere using two‐photon polymerization.     

碳纳米管／PA6纳米复合材料的制备及力学性能

采用RAFT活性聚合反应在碳纳米管表面接枝聚甲基丙烯酸甲酯(二硫代酯化合物作RAFT试剂),并制备了碳纳米管/PA6纳米复合材料。利用FT-IR、TEM、SEM、TGA等测试方法表征接枝聚合物后的碳纳米管,考察了碳纳米管的用量对碳纳米管/PA6纳米复合材料力学性能的影响,并观察了碳纳米管/PA6纳米复合材料冲击断面形貌。结果表明,聚合物接枝到了碳纳米管表面,碳纳米管/PA6纳米复合材料的力学性能明显提高。     

Microfluidic‐Based Approaches in Targeted Cell/Particle Separation Based on Physical Properties: Fundamentals and Applications

Cell separation is a key step in many biomedical research areas including biotechnology, cancer research, regenerative medicine, and drug discovery. While conventional cell sorting approaches have led to high‐efficiency sorting by exploiting the cell's specific properties, microfluidics has shown great promise in cell separation by exploiting different physical principles and using different properties of the cells. In particular, label‐free cell separation techniques are highly recommended to minimize cell damage and avoid costly and labor‐intensive steps of labeling molecular signatures of cells. In general, microfluidic‐based cell sorting approaches can separate cells using “intrinsic” (e.g., fluid dynamic forces) versus “extrinsic” external forces (e.g., magnetic, electric field, etc.) and by using different properties of cells including size, density, deformability, shape, as well as electrical, magnetic, and compressibility/acoustic properties to select target cells from a heterogeneous cell population. In this work, principles and applications of the most commonly used label‐free microfluidic‐based cell separation methods are described. In particular, applications of microfluidic methods for the separation of circulating tumor cells, blood cells, immune cells, stem cells, and other biological cells are summarized. Computational approaches complementing such microfluidic methods are also explained. Finally, challenges and perspectives to further develop microfluidic‐based cell separation methods are discussed.     

Recent advances and an industrial perspective of cellulose nanocrystal functionalization through polymer grafting

Cellulose nanocrystals (CNCs) are an emerging nanomaterial for applications ranging from coatings and construction to adhesives and biomedical devices. Owing to their high aspect ratio, stiffness, and reinforcing potential, CNCs have shown great promise to be used in polymer nanocomposites. However, due to their inherent hydrophilicity and compatibility with polar environments, the use of CNCs in hydrophobic polymer matrices or in organic solvent-based formulations has been limited. To overcome this incompatibility, many reports on grafting polymers onto the surface of CNCs have been published over the past ten years. This review describes the recent advances in CNC surface functionalization through polymer grafting, and comprehensively covers the existing work to date. Methods including polymer “grafting to” and “grafting from” are described in detail, using polymerization techniques such as free radical, ring opening, and controlled radical polymerization. Purification and characterization of polymer-grafted CNCs, the potential for upscaling these functionalization methods, and current perspectives from academic and industrial viewpoints are presented.     

Direct CVD Growth of Graphene on Traditional Glass: Methods and Mechanisms

Chemical vapor deposition (CVD) on catalytic metal surfaces is considered to be the most effective way to obtain large‐area, high‐quality graphene films. For practical applications, a transfer process from metal catalysts to target substrates (e.g., poly(ethylene terephthalate) (PET), glass, and SiO₂/Si) is unavoidable and severely degrades the quality of graphene. In particular, the direct growth of graphene on glass can avoid the tedious transfer process and endow traditional glass with prominent electrical and thermal conductivities. Such a combination of graphene and glass creates a new type of glass, the so‐called “super graphene glass,” which has attracted great interest from the viewpoints of both fundamental research and daily‐life applications. In the last few years, great progress has been achieved in pursuit of this goal. Here, these growth methods as well as the specific growth mechanisms of graphene on glass surfaces are summarized. The typical techniques developed include direct thermal CVD growth, molten‐bed CVD growth, metal‐catalyst‐assisted growth, and plasma‐enhanced growth. Emphasis is placed on the strategy of growth corresponding to the different natures of glass substrates. A comprehensive understanding of graphene growth on nonmetal glass substrates and the latest status of “super graphene glass” production are provided.     

The Pathway to Intelligence: Using Stimuli‐Responsive Materials as Building Blocks for Constructing Smart and Functional Systems

Systems that are intelligent have the ability to sense their surroundings, analyze, and respond accordingly. In nature, many biological systems are considered intelligent (e.g., humans, animals, and cells). For man‐made systems, artificial intelligence is achieved by massively sophisticated electronic machines (e.g., computers and robots operated by advanced algorithms). On the other hand, freestanding materials (i.e., not tethered to a power supply) are usually passive and static. Hence, herein, the question is asked: can materials be fabricated so that they are intelligent? One promising approach is to use stimuli‐responsive materials; these “smart” materials use the energy supplied by a stimulus available from the surrounding for performing a corresponding action. After decades of research, many interesting stimuli‐responsive materials that can sense and perform smart functions have been developed. Classes of functions discussed include practical functions (e.g., targeting and motion), regulatory functions (e.g., self‐regulation and amplification), and analytical processing functions (e.g., memory and computing). The pathway toward creating truly intelligent materials can involve incorporating a combination of these different types of functions into a single integrated system by using stimuli‐responsive materials as the basic building blocks.     

Ink‐Free Reversible Optical Writing in Monolayers by Polymerization of a Trifunctional Monomer: Toward Rewritable “Molecular Paper”

A Langmuir–Blodgett film consisting of a dense array of trifunctional monomers bearing three 1,8‐diazaanthracene units is polymerized at an air/water interface or after transfer on solid substrates. The transfer does not affect the excimer fluorescence of the film, indicating that the monomers' packing with their diazaanthracene units stacked face‐to‐face is retained—a prerequisite for successful polymerization. The monomer film can be polymerized in confined areas on solid substrates by UV irradiation with a confocal microscope laser. The underlying chemistry of the polymerization, a [4+4]‐cycloaddition of the diazaanthracene units, leads to disappearance of the fluorescence in the irradiated regions which enables writing into the monolayer on a µm scale—thus the term “molecular paper.” The reaction can be reversed by heating which leads to a recovery of the fluorescence and to erasing of the writing. Alternative pathways for this phenomenon are discussed and control experiments are conducted to rule them out.     

"活性"/可控自由基聚合制备含糖聚合物的研究进展

含有糖单元的聚合物因其在药学和生物技术等领域的潜在应用价值吸引了科研工作者的广泛关注.文中介绍了原子转移自由基聚合(ATRP),氮氧稳定自由基聚合(NMP),可逆加成断裂链转移聚合(RAFT)等"活性"/可控自由基聚合在制备含糖聚合物中的应用进展,重点介绍了上述三种聚合方法对含糖聚合物分子量和结构的控制.