Hybrid polymer latexes

Hybrid polymer latexes will be defined here as colloidal dispersions in which at least two distinct polymers exist within each particle. The two polymers may form a homogenous blend within the particle or microphase separation may occur. There are two general routes for their preparation. The first involves the use of a mini-emulsion polymerization process, in which a first polymer, most often prepared via polycondensation (or polyaddition), is dissolved in an unsaturated monomer (or a mixture of monomers). The solution is first emulsified into small droplets under a high shear process and then polymerized through a radical polymerization process. A variation of this route involves the synthesis of the polycondensate directly in the mini-emulsion. The second route involves a seeded emulsion polymerization of unsaturated monomer(s), in which the polycondensate is modified for use as a seed in the emulsion polymerization. Most often, styrenic and acrylic monomers are used, while the polycondensate may be alkyd resins, polyesters, epoxy resins, polyurethanes, or other polymers. The two routes are described in detail, as are the properties of the resulting materials (mostly as films). Up to now, there have been very few trials for the comparison of the two main routes. Most often the comparison is related to blends of the two kinds of emulsified polymers.     

A study on the synthesis of acrylic composite particles and investigation of their characterization

Core-shell latexes were synthesized by sequential emulsion polymerization of methyl methacrylate (MMA), styrene (St), and ethyl acrylate (EA) in the presence of anionic surfactant, and the characteristics of these latexes were evaluated. The core latex had to be synthesized carefully to avoid the formation of secondary particles. The sequential polymerization method adopted for this synthesis took advantage of stabilizing particles grown during shell polymerization. In core-shell latex polymerization, to suppress the generation of new particles and to minimize the gelation during the shell polymerization, the amount of surfactant (Sodium dodecyl benzene sulfonate: SDBS) should be reduced to the minimum, 0.01 wt% and 0.02 wt% of SDBS to amount of monomer, respectively, when the Polymethyl methacrylate (PMMA) and Polystyrene (PSt) core latexes are prepared. In addition, the monomer pre-emulsion method is better than monomer-add method. The core-shell structure for composite latex synthesized was demonstrated by Particle Size Analysis (PSA), Differential Scanning Calorimeter (DSC), Transmission Electron Microscope (TEM), formability of film, and hydrolysis under NaOH solution.     

Rheology of acrylic dispersions for pressure sensitive adhesives

Pressure sensitive adhesives (PSA) can be defined as adhesive materials which, when dry, possess a lasting and aggressive tack which enables them to adhere to a wide variety of substrates, upon contact. The interest in aqueous acrylic dispersions PSA grew with the need to solve solvent emission problems. The theological characteristics of these PSA dispersions are important for the coating machinability whilst the rheological characteristics of the dried PSA dispersions are important for the performance of the adhesive systems. The rheology of these dispersions, which are generally applied at a concentration in the range of 50% dry material, is influenced by parameters such as particle size, the nature of the acidic monomers, the method of introduction of the acidic monomers, the addition of thickeners and many others which are not covered in this paper. The flow characteristics (shear stress versus shear rate) of these dispersions can be described by means of mathematical models and therefore characterized by a limited number of parameters. The adhesive test methods commonly used today are largely the result of empirical attempts to characterize adhesive performance under actual conditions. The more-common tests are used in order to quantify tack, adhesion and cohesion. We have defined some testing methods in order to characterize the viscoelasticity of the PSA (dynamic measurements at different temperatures and frequencies and creep measurements at different temperatures). We have correlated these rheological parameters to the adhesive performances and the molecular characteristics of the acrylic copolymer used.     

Nonionic surfactant-stabilized raspberry-like polymer/silica nanoparticles latex with film formability

Raspberry-like P(St-BA)/SiO₂ nanoparticle latexes were prepared via miniemulsion polymerization of styrene (St) and butyl acrylate (BA) in the presence of 20 nm glycerol-modified SiO₂ sol as a Pickering emulsifier and octaphenyl polyoxyethylene (CA-897) as a nonionic surfactant, using 2,2-azobis (isobutyronitrile) (AIBN) as an initiator. 2-(Methacryloyl) ethyltrimethylammonium chloride (MTC) was introduced to act as an auxiliary monomer to enhance the attraction of SiO₂ sol onto latex nanoparticles (NPs) via increasing their electrostatic interaction with negative-charged SiO₂ sol. The average particle sizes of the latex particles can be well controlled from 200 to 360 nm by variation of the SiO₂ sol content as well as soft monomer BA component. The latex NPs displayed a good colloidal stability with excellent resistance to both strong acidic and basic environment. Furthermore, the nanosized latexes exhibited good film formability. The influence of reaction parameters, e.g., the initial silica amount and soft monomer BA content was systematically investigated on the film performances, such as hardness, abrasive resistance, water absorption, gloss. The results indicated that the increase of SiO₂ sol content can contribute to the increase of the film hardness and water absorption ability, while increasing BA component is beneficial to the improvement of the film gloss.     

不同离子类型聚氨酯/纳米SiO2复合乳液的制备及性能比较

分别采用2,2-二羟甲基丙酸、N-甲基二乙醇胺和聚醚二元醇作为亲水基团,γ-氨丙基三乙氧基硅烷(KH-550)为预聚体封端剂,采用溶胶凝胶法合成阴(ASPU)、阳(CSPU)和非离子型(NSPU)聚氨酯/纳米Si O2的复合乳液。采用粒径分析、SEM、FTIR、DSC、TGA、XRD和拉力机等对3种复合材料的乳液状态、膜结构和性能进行表征。结果显示,在软硬段结构相同的条件下,NSPU的平均粒径最大;复合材料中PBA2000的结晶度大小的顺序为:NSPUCSPUASPU;拉伸强度和邵氏硬度大小的顺序为:ASPUCSPUNSPU;ASPU和CSPU胶膜的力学性能、热性能和耐水性较好,NSPU胶膜的柔顺性和耐酸碱性较好。     

不同离子类型聚氨酯/纳米SiO2复合乳液的制备及性能比较

分别采用2,2-二羟甲基丙酸、N-甲基二乙醇胺和聚醚二元醇作为亲水基团,γ-氨丙基三乙氧基硅烷（KH-550）为预聚体封端剂,采用溶胶凝胶法合成阴（ASPU）、阳（CSPU）和非离子型(NSPU)聚氨酯/纳米SiO2的复合乳液。采用粒径分析、SEM、FT-IR、DSC、TGA、XRD和拉力机等对3种复合材料的乳液状态、膜结构和性能进行表征。结果显示,在软硬段结构相同的条件下,NSPU的平均粒径最大;复合材料中PBA2000的结晶度大小的顺序为：NSPU>CSPU>ASPU;拉伸强度和邵氏硬度大小的顺序：ASPU>CSPU>NSPU;ASPU和CSPU胶膜的力学性能、热性能和耐水性较好,NSPU胶膜的柔顺性和耐酸碱性较好。     

A mesoporous SiO2/TiO2 composite used for various emulsions separation

A mesoporous SiO₂-TiO₂-x composite without any modification was obtained to separate oil-in-water and water-in-oil emulsions solely by gravity. To simulate the actual pollution treatment process in sewage treatment plants, adsorption and degradation properties were studied after the initial emulsion separation. The research result indicates that the reported mesoporous SiO₂ can be employed as an excellent absorbent and catalyst carrier. After light irradiating for 120 min, the degradation efficiency of SiO₂-TiO₂-4 for Rhodamine B, methyl orange, methylene blue, and ciprofloxacin hydrochloride reaches 99.3%, 91.5%, 98.7%, and 96.2%, respectively.     

Emulsion atom transfer radical polymerization of 2-ethylhexyl methacrylate

The emulsion atom transfer radical polymerization (ATRP) of 2-ethylhexyl methacrylate (EHMA) was carried out with ethyl 2-bromoisobutyrate (EBiB) as an initiator and copper bromide (CuBr)/4,4′-dinonyl-2,2′-bipyridyl (dNbpy) as a catalyst system. The effects of surfactant type and concentration, temperature, monomer/initiator ratio, and CuBr₂ addition on the system livingness, polymer molecular weight control, and latex stability were examined in detail. It was found that the polymerization systems with Tween 80 and Brij 98 as surfactants at 30 °C gave the best latex stability. The polymer samples prepared under these conditions had narrow molecular weight distributions (M_w/M_n=1.1-1.2) and linear relationships of number-average molecular weight versus monomer conversion.     

交联型聚硅氧烷/聚丙烯酸酯复合乳液的制备

在甲基丙烯酰氧丙基三甲氧基硅烷存在下，以交联的聚硅氧烷为种子，丙烯酸酯单体为第二单体，偶氮二异丁腈为引发剂，分别采用间歇法、溶胀法和半连续法制备了聚硅氧烷／聚丙烯酸酯复合乳液。采用透射电子显微镜对乳胶粒子形态进行了表征，发现乳液中形成了以聚丙烯酸酯为核、聚硅氧烷为壳的反相核壳结构乳胶粒子；放置90天后，乳胶粒子的形态未发生翻转；将复合乳液破乳后分析，聚合物凝胶量达到96％以上，说明聚合体系交联很好。     

Polystyrene/melamine-formaldehyde hollow microsphere composite by self-assembling of latex particles at emulsion droplet interface

Submicron scale particle aggregates with defined shape were prepared by self-assembling of sulphonated polystyrene latex particles at the interface of emulsion droplets. Several parameters were considered during the preparation, including the sulphonation time of the polystyrene latex particles, the composition of the oil phase, and the zeta potential of the sulphonated latex particle. To further improve the mechanical stability of the particle aggregates, a hard composite layer was formed by addition of melamine-formaldehyde (MF) prepolymer into the emulsion. The prepolymer was crosslinked onto the particles surface of sulphonated PS particle aggregates. The crosslinking reaction was catalysed by the acidity of sulfogroup. After evaporating off solvent, PS/MF hollow microsphere composites were obtained as mechanically stable dry material. The hollow microsphere composite was characterized by TGA, FTIR, optical microscopy, scanning and transmission electron microscopy.