Ultracentrifugation Method to Measure Water-Soluble Monomer Incorporation in Latex

Emulsion copolymerizations involving water-soluble functional monomers such as N-methylolacrylamide often result in the formation of water-soluble polymer that remains in the aqueous phase of the latex. A simple procedure is developed to determine the amount of water-soluble polymer in the aqueous phase of a high-solids latex using ultracentrifugation. Dilution of the latex with water is usually found necessary for good separation during ultracentrifugation. If the latex contains a surface-active species (surfactant) in amounts comparable to the amount of water-soluble polymer, calculation of the amount of water-soluble polymer in the serum of the original latex will require information about dilution dependent partitioning of the surfactant between the surface of the particles and the aqueous phase. This paper outlines a procedure that enables determination of the amount of water-soluble polymer in the aqueous phase of the original latex, by ultracentrifugation of the latex diluted to different concentrations. The procedure also gives the Henrys constant for the adsorption of the surfactant on the surface of the polymer particles in the latex.     

有机硅改性丙烯酸酯共聚乳液合成方法及胶膜性能的研究

用一次投料法、单体乳液滴加法和引发剂滴加法有机硅改性丙烯酸酯共聚乳液，聚合过程、胶粒形态及乳液稳定性的观测结果表明：单体乳液滴加法是合成该类乳液的最佳方法，研究了单体乳液滴加法中有机硅含量与聚合反及胶膜性能的关系，结果表明：有机硅含量在１５％以下时，聚合反应可以顺利进行，胶膜性能不仅依赖于聚合时有机硅单体的总量，而且还依赖于有机硅单体中活性硅氧烷所占的比例。     

The application of dielectric analysis to drying latex films

Measurements of real and imaginary capacitance (C andC) have been made during the drying of a film-forming latex. In one experiment dielectric measurements at frequencies between 1 Hz and 100 kHz were made simultaneously with gravimetric measurements on a microbalance. It was found that both the rate of water evaporation and the a.c. conductance decrease sharply at high polymer volume fraction. These results are discussed qualitatively in terms of a model for the film-forming process. In another experimentC andC were recorded at 10 Hz along with automatic measurements of the build-up of the scratch resistance of the film. It was found that the mechanical response to film-formation appears significantly earlier than the dielectric response. This is also discussed qualitatively in terms of the model.The authors would like to thank Dr. I. Abrahams, Dr. S. Bell, and Dr. M. Reading for useful discussions regarding this work and M. Bahra for his help with the TFA measurements.     

Amphoteric polystyrene latex colloids: polymerization pathway and the control of particle size and potential

Amphoteric polystyrene latex colloids were prepared by the emulsifier-free emulsion polymerization of styrene. Two co-monomers, methacrylic acid (MA) (anionic) and dimethyl aminoethyl methacrylate (DMAM) (cationic) were used to promote the amphoteric nature of the resultant surfaces. Parameters such as particle size and the isoelectric point (IEP) were measured as a function of polymerization recipe. Particle size decreased with increasing initiator concentration according to the equation: log [d _w]=–0.67 log [I] + 0.316 whered _w is the weight average particle diameter andI is the concentration of initiator (potassium persulphate).The particle size also decreased with increasing temperature, increasing pH and addition of surfactant. Particle size was unaffected by the methacrylic acid content. The isoelectric point pH was decreased on decreasing initiator concentration and on increasing methacrylic acid content.The polymerization pathway was deduced to involve the cationic DMAM during the initiation phase and to involve the anionic MA as well as styrene, during the growth stage. A full polymerization pathway involving the formation of oligomeric DMAM micelles was postulated.     

Synthesis of water-soluble hyperbranched polymer and its application in acrylic latex

A water-soluble hyperbranched polymer (WHBP), obtained from a second generation of hyperbranched polyester and maleic anhydride, was studied. Its effects on the properties of acrylic latexes, which were based on emulsion polymerization of butyl acrylate (BA), methyl methacrylate (MMA), acrylic acid (AA) and WHBP, and latex film were discussed. The characteristics of WHBP were determined by nuclear magnetic resonance spectroscopy (NMR), Fourier transform infrared (FTIR) and gel permeation chromatography (GPC). Particle size and morphology of latex particles were confirmed by dynamic light scattering (DLS) and transmission electron microscope (TEM). The investigation showed that WHBP could be used in emulsion polymerization, and that latex of poly(BA-MMA-WHBP) was more stable than that of poly(BA-MMA-AA). The hardness of latex film increased from 2B to HB when WHBP was used.     

Competitive adsorption of an anionic and a nonionic surfactant on polystyrene latex particles as monitored by small x-ray scattering

Adsorption of the anionic surfactant sodium dodecylsulfate (SDS) as well as competitive adsorption of SDS with the nonionic surfactant Triton X-405 on a polystyrene latex has been examined by the use of small-angle x-ray scattering (SAXS). Since the latex particles only have a low contrast towards water whereas the electron densities of the added surfactants are rather high, their gradual adsorption can be monitored with good sensitivity. The particles covered with SDS have been investigated by the contrast variation method. A distinct core-shell structure has been observed. After maximum coverage of the surface is reached, the additional surfactant forms free micelles. The analysis presented here allows the simultaneous investigation of the covered particles and the free micelles. This is due to their respective characteristic scattering contributions in different angular ranges. Information on the competitive adsorption could be obtained by analyzing the structure of the coated particles and the composition of the free mixed micelles. The adsorption is shown to be an equilibrium process where adsorption of the nonionic component is found to be much stronger than of the SDS molecules.     

Photochemical aging of in situ polymerized blends of polystyrene and poly[acrylonitrile-g-(ethylene-co-propylene-co-diene)-g-styrene] (AES)

The influence of photochemical aging of in situ polymerized PS/AES blends on their mechanical properties has been studied. The PS/AES blends were subjected to photochemical aging for 168 h and 720 h. Tensile properties and Izod impact resistance of aged and non-aged samples were evaluated. The mechanical properties of the PS/AES blends are influenced by the polymerization temperature and blend composition and represent a balance between the toughness of EPDM and the stiffness of SAN in the PS matrix. Even though the impact resistance and strain at break of HIPS are higher than those of the PS/AES blends, after the aging period all PS/AES blends showed higher strain at break than HIPS. PS/AES blends present higher photochemical stability than HIPS.     

Electrostatic interactions between amphoteric latex particles and proteins

The electrostatic interactions between amphoteric polymethyl methacrylate latex particles and proteins with different pI values were investigated. These latex particles possess a net positive charge at low pH, but they become negatively charged at high pH. The nature and degree of interactions between these polymer particles and proteins are primarily controlled by the electrostatic characteristics of the particles and proteins under the experimental conditions. The self-promoting adsorption process from the charge neutralization of latex particles by the proteins, which have the opposite net charge to that of the particles, leads to a rapid reduction in the zeta potential of the particles (in other words colloidal stability), and so strong flocculation occurs. On the other hand, the electrostatic repulsion forces between similarly charged latex particles and the proteins retard the adsorption of protein molecules onto the surfaces of the particles. Therefore, latex particles exhibit excellent colloidal stability over a wide range of protein concentrations. A transition from net negative charge to net positive charge, and vice versa (charge reversal), was observed when the particle surface charge density was not high enough to be predominant in the protein adsorption process.     

Preparation and characterization of novel organic chelating resin and its application in recovery of Zn(II) from aqueous solutions

An organic polymeric resin was synthesized by anchoring p ‐aminobenzoic acid onto macroporous chloromethylated polystyrene beads, and was used for Zn(II) removal from aqueous solutions. The resin exhibited an initially rapid adsorption property for Zn(II) with equilibrium time of 10 h and the maximum adsorption capability approached 184.5 mg g⁻¹. Optimum pH was 4.5. The mechanism of adsorption was investigated using kinetic, isotherm and thermodynamic models. The adsorption kinetic data were described well by a pseudo second‐order model with R ² of 0.997. There was a negative ΔG (−17.98 kJ mol⁻¹) and positive ΔH (13.58 kJ mol⁻¹). HCl solution (1.0 mol l⁻¹) could achieve an elution rate of 100%. The experimental data were well fitted by the Thomas model with R ² of 0.9826. Copyright © 2016 John Wiley & Sons, Ltd.     

微米级PS-PEDOT核壳型导电微球的合成与拉曼表征

以分散聚合法制备的微米级聚苯乙烯(PS)微球为模板、3,4-乙烯二氧噻吩(EDOT)为单体、过硫酸铵(APS)为引发剂,通过氧化聚合制备了PS-PEDOT核壳型复合导电微球。采用扫描电镜、透射电镜等对导电微球的形貌和结构进行了表征,重点采用拉曼光谱研究了其核壳结构特征。并研究了超声分散、溶液pH以及单体配比对导电微球形貌的影响。实验结果表明:超声的引入可提高导电微球的单分散性,改善微球的形貌。随着pH的降低或单体配比的增加,导电聚合物在PS微球表面的负载量随之增加,当m(EDOT)/m(PS)由0.60增加到1.25时,导电微球的平均粒径由1.76μm增加到1.91μm。