Facile synthesis of fluorescent quantum dot‐polymer nanocomposites via frontal polymerization

We report an available approach for quickly fabricating CdS QD‐polymer nanocomposites via frontal polymerization (FP). First, we synthesized (3‐mercaptopropyl)‐1‐trimethoxysilane (MPS)‐capped CdS quantum dots (QDs). With these MPS‐capped CdS QDs containing mercapto groups, MPS‐capped CdS QDs can be easily incorporated into a poly(N‐methylolacrylamide) (PNMA) matrix via FP. A variety of features for preparing QD‐polymer nanocomposites, such as initiator concentration and CdS concentration, were thoroughly investigated. The fluorescence properties of QD‐polymer nanocomposites prepared via FP are comparatively investigated on the basis of ultraviolet–visible (UV–vis) spectra and photoluminescence (PL) spectra. Results show that the PL intensity of QD‐polymer nanocomposites prepared via the FP method is superior to that obtained by the traditional batch polymerization (BP) method. In addition, by measuring the changes of PL intensity of the samples immersed in different concentrations of copper acetate solution, we found the QD‐polymer nanocomposites can be ultrasensitive to copper ions. This FP process can be exploited as a facile and rapid way for synthesis QD‐polymer nanocomposites on a large scale, avoiding the fluorescence quenching of nanocrystals during incorporation nanocrystals into polymer matrices. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 2170–2177, 2010     

Synthesis of single‐core and multiple‐core core‐shell nanoparticles by RAFT emulsion polymerization: Lead sulfide‐copolymer nanocomposites

We report here a simple and direct route for the preparation of lead sulfide (PbS) quantum dots (QDs) embedded into polymeric nanospheres by emulsion polymerization. In this process, QDs are first dispersed in an aqueous solution containing a statistical oligomer constituted of five butyl acrylate and ten acrylic acid units prepared by reversible addition fragmentation chain transfer (RAFT) polymerization using a trithiocarbonate as RAFT agent. Then, the dispersion of PbS QDs is engaged into an emulsion polymerization process to form core‐shell nanoparticles. Transmission electron microscopy reveals the presence of single‐core core‐shell particles at low concentration of PbS QD, whereas multiple‐core core‐shell particles containing either well separated or aggregated PbS QDs are formed at high concentration of PbS QDs. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012     

Polymer coating of graphene oxide via reversible addition–fragmentation chain transfer mediated emulsion polymerization

This work describes a versatile method to encapsulate graphene oxide (GO) with polymers using reversible addition‐fragmentation chain transfer (RAFT) mediated emulsion polymerization. A living low molecular weight anionic macro‐RAFT statistical copolymer of sodium styrene sulfonate, acrylic acid, and butyl acrylate (BA) was synthesized using 2‐{[(butylsulfanyl)carbonothioyl] sulfanyl} propanoic acid as the chain transfer agent. GO was dispersed in water by pretreating the surface with poly(allylamine hydrochloride) (PAH), before being stabilized by the addition of the anionic macro‐RAFT copolymer. PAH was used to facilitate the adsorption of the macro‐RAFT copolymer to the GO surface via electrostatic attraction between opposite charges. The dispersed GO sheets were encapsulated with polymer by the free radical emulsion polymerization of methyl methacrylate and BA under starved fed conditions. The polymer shells encapsulating the GO sheets were formed by the chain extension of the adsorbed living macro‐RAFT copolymer. TEM, SEM, FTIR, and AFM were used to confirm the presence of the polymer layer on the surface of the GO. The thickness of the polymer coating can be adjusted by controlling the amount of monomer fed into the system. Partial polymer coatings of the GO could be achieved by varying the amount of PAH. The encapsulated GO was found to be easily dispersed in both aqueous and organic solvents over a range of polarities. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 1413–1421     

Surface-tunable photoluminescence from block copolymer-stabilized cadmium sulfide quantum dots

The static and time-resolved photoluminescence properties of polystyrene-b-poly(acrylic acid) (PS-b-PAA)-stabilized cadmium sulfide quantum dots (CdS QDs) have been characterized for the first time, demonstrating tunable emission spectra and quantum yields via different chemical treatments of the PAA layer. Samples with the PAA layer in its cadmium carboxylate form showed more-intense band-edge emission and relatively high quantum yields compared with samples in which the PAA layer was in its acid form. This activation effect is explained in terms of passivation of trap sites on the QD surface by specific interactions between the QD and the cadmium-neutralized PAA layer. Lifetimes of band-edge and trap state emission for the various samples ranged from 40 to 61 ns and 244 to 360 ns, respectively. Impressive long-term stability was also shown for a sample of cadmium-neutralized PS-b-PAA-stabilized QDs dispersed in toluene, which maintained 90% of its photoluminescence over 57 days aging under ambient conditions. It is also shown that Cd2+ activation of photoluminescence does not occur when Mg2+ ions are added to similar QD solutions, indicating potential of these block copolymer-stabilized QDs as Cd2+-selective sensors. Irrespective of chemical treatment of the PAA layer, the external PS brush layer effectively stabilized all samples in various organic solvents, resulting in clear CdS colloids with no observed precipitation over several months. Dynamic light scattering and gel permeation chromatography revealed differences in the aggregation numbers and hydrodynamic radii of colloidal QDs for different treatments of the PAA layer, attributed to the lower solubility of the poly(cadmium acrylate) blocks compared to the PAA blocks in the acid form. Finally, it was demonstrated that the PS-b-PAA-stabilized QDs could be well dispersed in PS homopolymer, producing optically transparent photoluminescent films which retained the emission features of the colloidal QDs. Stable and surface-tunable optical properties via the PAA layer and polymer solubility and processability via the PS layer make these PS-b-PAA-stabilized CdS QDs exciting "building blocks" for the bottom-up assembly of functional hierarchical materials for photonics, sensors, and bio-labeling applications.     

Preparation and characterization of pure polyacrylate polymer colloid through emulsion polymerization using a novel initiator

A series of acrylic polymer colloids were prepared via semi-continuous seeded emulsion polymerization of BA and MMA in water phase when OP-10 and AIBI is used to be emulsifier and initiator, respectively. FTIR spectrum identifies the formation of copolymers of P (MMA-co-BA). DSC confirms that the colloid is a kind of random copolymer and the consistency among the chain segment is fairly good. The emulsion polymerization conditions of preparing acrylic polymer colloid are optimized. Results show that the conversion rate is high and the coagulum is low and the particle size of the acrylic polymer colloids is small when the amount of AIBI is 0.75 g. The polymerization temperature is 70 °C, which is lower than the one that the emulsion polymerization is initiated with the persulfate.     

Design and Preparation of Highly Filled Water‐Borne Polymer–Gibbsite Nanocomposites

Highly filled, high solids content, water‐borne polymer–Gibbsite nanocomposites are prepared with Gibbsite contents as high as 35 wt%. The polymer–Gibbsite nanocomposites are synthesised via conventional starved feed emulsion polymerization using negatively charged butyl acrylate‐co‐acrylic acid oligomers, which functioned as electrosteric stabilizers for the initial platelets and the subsequently formed latex particles. A simple mathematical model describing the amount of cooligomer required for the colloidal stability of the initial Gibbsite platelets and the subsequently formed particles was derived. This model was used to determine the reaction conditions required for obtaining colloidally stable nanocomposites with a targeted filler content. Cryogenic transmission electron microscopy characterization of the resulting nanocomposites with filler contents up to 20 wt% revealed fully encapsulated Gibbsite platelets and a mixed morphology of “muffin‐like” and encapsulated particles was obtained at higher filler contents.     

基于聚合物多齿配体的高性能CdTe量子点的微波水相合成

针对当前水相合成的量子点(QDs)光性能与稳定性等方面存在的不足,发展了基于聚合物多齿配体的水相制备策略.利用巯基修饰的聚丙烯酸(PAA-SH)作为多齿配体代替常用的巯基丙酸等单齿配体,结合微波辅助加热制备了CdTe量子点,研究了多齿配体对量子点的生长机制与荧光性能的影响.以PAA-SH为配体制备的CdTe量子点荧光性能优异(荧光量子效率(PLQY)可达75%),流体力学直径较小(~10 nm),稳定性也有明显提高.基于聚合物多齿配体的量子点制备技术有助于实现生物医学研究中急需的兼具高亮度、高稳定性、小尺寸等特征的高性能量子点生物探针的制备.     

Preparation and characterization of latices with hydrophobic core and hydrophilic shell

Anionic and non-ionic copolymer latices with a hydrophobic core and hydrophilic shell were prepared using emulsifier-free emulsion polymerization. Styrene was used as the hydrophobic monomer; acrylic acid, acrylamide, and methacrylamide were employed as the hydrophilic monomers. The amount of chemically bound hydrophilic monomers in latex and unbound homopolymers in water were determined. The salt stability and redispersability of latices in water after spray-drying were also investigated.     

Preparation of poly (styrene-methyl methacrylate)/SiO2 composite nanoparticles via emulsion polymerization. An investigation into the compatiblization

Inorganic/organic nanocomposite systems, in which inorganic particles are encapsulated into the polymer matrix, are new classes of polymeric materials. These materials combine the properties of both components. It means that polymer component with excellent optical property, flexibility and toughness could improve the brittleness of inorganic particles and besides, inorganic particles could increase the strength and modulus of polymers. There are various methods to make these inorganic/organic nanocomposites. One of them is the chemical process, in which polymerization is performed directly in the presence of the inorganic particles. Examples of miniemulsion, suspension or dispersion polymerization can be found in the literature but emulsion polymerization is by far the technique most frequently used.In this work, latex containing nanostructure hybrid of copolymer (styrene, methyl methacrylate, acrylic acid) and inorganic nanoparticles (silica) with core/shell structure was prepared via semi-batch emulsion polymerization. At first, silica nanoparticles were dispersed in water phase in an ultrasound bath to prevent the aggregation of nanoparticles, and then emulsion polymerization was performed in the presence of silica nanoparticles. Related tests and analysis confirmed the success in synthesis of nanostructure hybrids. Induced coupled plasma (ICP) analysis and thermal gravimetric analysis (TGA) showed the presence and amount of silica nanoparticles in the final latex. Dynamic light scattering (DLS) analysis confirmed the presence of 25-35 nm particles in the system and transmission electron microscopy (TEM) showed the core/shell morphology of nanoparticles. It has been shown that with an appropriate surfactant, adjusting the pH of media, using suitable monomers and under controlled conditions, it would be possible to produce stable organic/inorganic composite nanoparticles with core/shell structure. In another attempt and in order to investigate the effect of compatiblizing system, styrene-methyl methacrylate was copolymerized in the presence of modified silica particles with oleic acid as the inorganic dispersed phase at the same condition. Similar characterizations were performed in order to have a worthwhile comparison. The results for the late procedure show the effect of oleic acid in formation of aggregates as the core for polymeric nanocomposite particles.     

Cadmium sulphide quantum dots in morphologically tunable triblock copolymer aggregates

Cadmium sulfide (CdS) quantum dots (QDs) are formed within poly(ethylene oxide)-block-polystyrene-block-poly (acrylic acid) (PEO-b-PS-b-PAA) triblock copolymer aggregates of different architectures. These structures are obtained starting with the same ionically cross-linked primary micelles consisting of a cadmium acrylate core, a PS shell, and a PEO corona. One morphology is a worm-shaped micelle prepared in tetrahydrofuran (THF) in which the CdS QDs are surrounded by the PAA and aligned as a loose necklace in the PS matrix. The PEO serves as a corona around the PS rod. Another structure is a multicore spherical (ca. 50 nm) water soluble PS micelle, surrounded by PEO chains. The CdS particles within these two latter structures are formed by the reaction of cadmium ions present in the acrylate cores with hydrogen sulfide. In a third structure, the CdS QDs are located on the surface of PS micelles. A fourth spherical single-core micelle structure is postulated to exist in dilute THF solutions. The dimensions in all the aggregates can be controlled by the block length.     

One- and two-photon induced polymerization of methylmethacrylate using colloidal CdS semiconductor quantum dots

The development of one- and two-photon induced polymerization using CdS semiconductor quantum dots (QDs) and amine co-initiators to promote radical generation and subsequent polymerization is presented. Two-photon absorption (TPA) cross-section measurements, linear absorption, and transmission electron microscopy are used to characterize the QDs. The effectiveness of the co-initiators in increasing the efficiency of photopolymerization (polymer chains formed per excitation) is examined. Triethylamine was observed to be most effective, yielding quantum efficiencies of initiation of >5%. The interactions between the co-initiators and QDs are investigated with steady-state photoluminescence and infrared spectroscopies. Possible initiation mechanisms are discussed and supported by electrochemical data. Making use of the surface chemistry developed here and the large QD TPA cross-sections, two-photon induced polymerization is demonstrated. The large TPA cross-sections coupled with modest quantum efficiencies for initiation reveal the unique potential of molecularly passivated QDs as efficient two-photon photosensitizers for polymerization.     

可用于尾矿库区污染控制的生态修复剂的制备及性能研究

采用种子乳液聚合法,以水性聚氨酯为分散液,醋酸乙烯酯(VAc)、马来酸二丁酯(DBM)、丙烯酸(AA)为主单体,2-丙烯酰胺基-2-甲基丙磺酸(AMPS)为功能单体,成功制备了羧基型共聚乳液,进一步考察了AMPS用量对乳液基本性能的影响,并首次将其用于尾矿库区的生态修复。实验结果表明:当AMPS用量在3%时,该共聚乳液用于尾矿库区固定尾砂的效果最好,且该共聚乳液形成胶膜的拉伸强度与固定尾砂时抗压强度呈现正相关性。另外,通过共聚乳液对尾砂的抗热老化、抗冻耐温、保水性及固定重金属离子稳定性等研究发现,羧基型共聚乳液能够有效实现尾矿库区的污染控制。微生物实验说明,羧基型共聚乳液作为尾矿库区修复剂使用时,具有良好的生态效应。这表明所制备的羧基型共聚乳液能够用于尾矿库区的污染控制与生态修复。     

A hierarchical self-assembly route to three-dimensional polymer-quantum dot photonic arrays

We demonstrate a new hierarchical self-assembly strategy for the formation of photonic arrays containing quantum dots (QDs), in which sequential self-assembly steps introduce organization on progressively longer length scales, ranging from the nanoscale to the microscale regimes. The first step in this approach is the self-assembly of diblock copolymers to form block ionomer reverse micelles (SA1); within each micelle core, a single CdS QD is synthesized to yield the hybrid building block BC-QD. Once SA1 is completed, the hydrophobic BD-QD building blocks are blended with amphiphilic block copolymer stabilizing chains in an organic solvent; water addition induces secondary self-assembly (SA2) to form quantum dot compound micelles (QDCMs). Finally, aqueous dispersions of QDCMs are slowly evaporated to induce the formation of three-dimensional (3D) close-packed arrays in a tertiary self-assembly step (SA3). The resulting hierarchical assemblies, consisting of a periodic array of hybrid spheres each containing multiple CdS QDs, exhibit the collective property of a photonic stop band, along with photoluminescence arising from the constituent QDs. A high degree of structural control is possible at each level of organization by judicious selection of experimental variables, allowing various parameters governing the collective optical properties, including QD size, nanoparticle spacing, and mesocale periodicity, to be independently tuned. The resulting control over optical properties via successive self-assembly steps should provide new opportunities for hierarchical materials for QD lasers and all-optical switching.     

乳液聚合法制备聚合物与十二醇复合乳胶粒

通过乳液聚合法, 以苯乙烯、丙烯酸丁酯为主要单体, 以甲基丙烯酸为功能性单体, 以二乙烯基苯或二甲基丙烯酸乙二醇酯为交联剂, 制备了包覆有十二醇的聚合物复合颗粒. 通过动态光散射粒径仪和透射电镜观测乳胶粒粒径和形态, 气相色谱法测试了十二醇的包覆率, 并探讨了聚合过程中十二醇包覆率的变化情况. 结果表明十二醇的包覆率和十二醇与单体的质量比及单体转化率显著相关, 并且在聚合过程中包覆率存在先升后降的趋势. 实验发现十二醇包覆率的先升后降是由聚合物和十二醇的相容性不好引起的.     

Langmuir-Blodgett thin films of quantum dots: synthesis, surface modification, and fluorescence resonance energy transfer (FRET) studies

We describe herein studies on as-prepared hydrophobic ZnS-CdSe quantum dots (QDs) at the air-water interface. Surface pressure-area (pi-A) isotherms have been used to study the monolayer behavior. Uniform, lamellar multilayer thin films of QDs were deposited by the Langmuir-Blodgett (LB) technique. The role of two different surfactant systems commonly employed in the synthesis of these QDs (trioctylphosphine oxide-octadecylamine (TOPO-ODA) system and trioctylphosphine oxide-tetradecylphosphonic acid (TOPO-TDPA) system) on the monolayer behavior and the quality of thin films produced has been investigated. The thin films were characterized by quartz crystal microgravimetry (QCM), contact angle measurements, fluorescence spectroscopy, and transmission electron microscopy (TEM). These QD films were further modified by an amphiphilic polymer, poly(maleic anhydride-alt-1-tetradecene) (PMA). The hydrophobic interaction between the polymers and the surfactants attached to the QDs drove the self-assembly process. The carboxylic acid functional groups in the polymer were also used to immobilize avidin. We have demonstrated a proof of concept for the biosensing strategy wherein the avidin-coated QD films attracted biotinylated gold nanoparticles, resulting in fluorescence resonance energy transfer (FRET) quenching of the thin films.     

Controlled self-assembly of hydrophobic quantum dots through silanization

We demonstrate the formation of one-, two-, and three-dimensional nanocomposites through the self-assembly of silanized CdSe/ZnS quantum dots (QDs) by using a controlled sol-gel process. The self-assembly behavior of the QDs was created when partially hydrolyzed silicon alkoxide monomers replaced hydrophobic ligands on the QDs. We examined systematically self-assembly conditions such as solvent components and QD sizes in order to elucidate the formation mechanism of various QD nanocomposites. The QD nanocomposites were assembled in water phase or on the interface of water and oil phase in emulsions. The partially hydrolyzed silicon alkoxides act as intermolecules to assemble the QDs. The QD nanocomposites with well-defined solid or hollow spherical, fiber-like, sheet-like, and pearl-like morphologies were prepared by adjusting the experimental conditions. The high photoluminescence efficiency of the prepared QD nanocomposites suggests partially hydrolyzed silicon alkoxides reduced the surface deterioration of QDs during self-assembly. These techniques are applicable to other hydrophobic QDs for fabricating complex QD nanocomposites.     

Tandem synthesis of core-shell brush copolymers and their transformation to peripherally cross-linked and hollowed nanostructures

Core-shell brush copolymers were prepared on the basis of a tandem synthetic strategy and used as single molecular templates for the preparation of polymeric nanomaterials. An alkoxyamine-functionalized norbornene monomer was prepared and then polymerized by ring-opening metathesis polymerization. The well-defined polymer (Mn = 122 kDa, Mw/Mn = 1.13) contained one alkoxyamine functionality per repeat unit and was then used as a polyfunctional macroinitiator for sequential nitroxide-mediated radical polymerizations of isoprene and tert-butyl acrylate. The resulting well-defined brush copolymer (Mn = 1410 kDa, Mw/Mn = 1.23) was transformed to an amphiphilic core-shell brush copolymer comprising poly(isoprene)-b-poly(acrylic acid) grafts by hydrolysis. Subsequent cross-linking of the poly(acrylic acid) block segments afforded peripherally cross-linked brush copolymer nanostructures, which served, finally, as templates for hollowed nanoscale frameworks by ozonolysis of the poly(isoprene)-based cores. Each transformation led to dramatic changes in the nanoscale composition and structure which were detected by combinations of spectroscopic measurements, atomic force microscopy imaging in the solid state, and/or dynamic light-scattering characterization in aqueous solution.     

Preparation and artificial ageing tests in stone conservation of fluorosilicone vinyl acetate/acrylic/epoxy polymers

In this work, a series of fluorosilicone vinyl acetate/acrylic/epoxy (FVAE) polymers for protection of stone relics were prepared with different content of hexafluorobutyl methacrylate (HFBMA) by the seed emulsion polymerization process. Properties and structure of FVAE materials were characterized by Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TG), and transmission electron microscopy (TEM). Viscosity, particle size, surface tension, gel content, adhesion and surface hardness of polymer materials were also determined. Surface morphology of the stone sample was observed by scanning electron microscopy (SEM). Compared with a commercial copolymer, ethyl methacrylate/methyl acrylate (EM/MA, Paraloid B72), protection ability of the prepared FVAE polymer was investigated using artificial ageing tests such as the freeze-thaw aging test, acid aging test and the soluble salts aging test. It was found that the FVAE polymers prepared can effectively prevent corrosion caused by H⁺, formation of an interface crack and further weathering, which indicates their possible application in stone protection.     

Effects of altered reaction conditions on the synthesis of polyurethane-poly(2,2,2-trifluoroethyl methacrylate) triblock copolymer aqueous dispersion

Polyurethane-poly(2,2,2-trifluoroethyl methacrylate) (PU-PTFEMA) triblock copolymer aqueous dispersions were synthesized by three-step polymerization. In the first step, polyurethane prepolymers (PU) based on 2,4-toluene diisocyanate (TDI), polyether binary alcohol (N₂₂₀), α,α-dimethylol propionic acid (DMPA), hydroxypropyl acrylic acid (HPA), and butanediol (BDO) were prepared with butanediol as the chain extender and methylethylketon as solvent. The next step involved neutralization and dispersion in water, where prepolymers were neutralised by the addition of triethylamine (TEA). The last step was the seeded emulsion polymerization, where PU emulsion was used as seed, kalium persulfate (KPS) as initiator and 2,2,2-trifluoroethyl methacrylate (TFEMA) as comonomer. Factors influencing the synthesis of PU-PTFEMA copolymer aqueous dispersion were studied. Experimental data indicate that factors influencing the synthesis of PU-PTFEMA copolymer aqueous dispersion mainly involve reaction temperature, reaction time, the concentration of initiator, DMPA content, TFEMA content. Rotational viscometer and dynamic light scattering (DLS) were used to characterize the properties of copolymer aqueous dispersion.     

Assembly of Fe2O3 Nanoparticles with Polymer Microspheres by Encapsulated Copolymerization

Inorganic nanoparticles Fe₂O₃ in diameter of 3-5 nm have been assembled with polymer microspherer and then encapsulated in copolymer of St/BA/AA by polymerization process. Fe₂O₃ encapsulated microspheres can obtained through interaction between surface groups of the two component particles and by adjusting the pH value in the emulsion. Pre-treatment of the composite particles using a certain amount of surfactant before polymerization can give a good encapsulation.