Kinetic Study of Radical Polymerization v. Determination of Reactivity Ratio in Copolymerization of Acrylonitrile and Itaconic Acid by 1H‐NMR

Many reports exist in the literature about the application of ¹H and ¹³C‐NMR techniques to analyze the copolymer structure and composition and also determination of reactivity ratios. In this work, on‐line ¹H‐NMR spectroscopy has been applied to identify reactivity ratios of itaconic acid and acrylonitrile in the solution phase (DMSO as the solvent) and in the presence of AIBN as the radical initiator. All the peaks corresponding to the existing protons were assigned quietly. Therefore, the kinetics of the copolymerization reaction was investigated by studying the variation of integral of two characteristic peaks regarding each monomer. The obtained data were used to find the reactivity ratios of acrylonitrile and itaconic acid by linear least‐squares methods such as Finemann‐Ross, inverted Finemann‐Ross, Mayo‐Lewis, Kelen‐Tudos, extended Kelen‐Tudos and Mao‐Huglin. In addition, a non‐linear least‐square method (Tidwell‐ Mortimer) was used at low conversions. Extended Kelen‐ Tudos and Mao‐Huglin were applied to determine reactivity ratio values at high conversions as well.     

N‐Vinylpyrrolidone and Ethoxyethyl Methacrylate Copolymer: Synthesis,Characterization and Reactivity Ratios

Free radical copolymerization of N‐vinyl‐2‐pyrrolidone with 2‐ethoxyethyl methacrylates was carried out with 2,2′‐azobisisobutyronotrile as an initiator in 1,4‐dioxane. The resulting copolymer was characterized by FTIR, H¹‐NMR and C¹³‐NMR spectroscopic techniques thermal properties of copolymer were determined by DSC and TGA. The reactivity ratios of the monomers were computed by the Fineman‐Rose (F‐R), Kelen‐Tudos (K‐T) and extended Kelen‐Tudos (EK‐T) method at lower conversion, using the data obtained from both FTIR and elemental analysis studies; the results are in good agreement with each other. The average reactivity ratio, Alfrey‐Price Q and e values were found to be r ₁=0.769, r ₂=0.266 and Q ₁=0.0859, e ₁=0.4508, respectively for NVP/EOEMA copolymer. The distribution of monomer sequence along the copolymer chain was calculated using a statistical method based on obtained reactivity ratio. The number average molecular weight and polydispersity were determined by GPC.     

Synthesis of Fluorinated Polyurethane/Polyacrylate Hybrid Emulsion Initiated by 60Co γ-Ray and Properties of the Latex Film

Based on the solvent-free method, novel fluorinated polyurethane/polyacrylate hybrid emulsions, dodecafluoroheptyl methacrylate (DFMA) as fluorinated monomer, were successfully prepared via emulsion polymerization without traditional emulsifier. For the purpose of increasing the grafting ratio of polyurethane and polyacrylate, ⁶⁰Co γ-ray radiation polymerization had been adopted to enhance the hardness of latex film. The chain structure and polymerization progress were confirmed by the analysis of Fourier transform infrared spectroscopy. The grafting ratio of polymethyl methacrylate and polyurethane was obtained by calculating the ratio of N–H peak integral area and Ph(C=C) peak integral area. The effect of DFMA content on thermal stability, mechanical property and water resistance were investigated systematically by thermal weight loss analysis, tensile strength test, absorbed water ratio and water contact angle.     

A Tensile Strain Hardening Test Indicator of Environmental Stress Cracking Resistance

Environmental stress cracking resistance (ESCR) is an important indicator of performance for high density polyethylene (HDPE) in structural and polymer pipe applications. The commonly used test for determining ESCR of HDPE can be time consuming and rather imprecise. A tensile strain hardening test was recently proposed to offer a faster way to characterize ESCR of polyethylene. In this paper, a practical approach is adopted whereby the test is extended to room temperature and shown to relate reliably to the ESCR of HDPE. Several HDPE resins (including pipe‐grade resins) are analyzed at strain rates of 0.5 mm/min and 7 mm/min to compare the effect of strain rate. Comparisons between the conventional ESCR test method and the strain hardening test show that strain hardening can be used to rank ESCR of HDPE in a reliable fashion. In our study the more direct measure of “hardening stiffness” is used to compare resins instead of strain hardening modulus. Because no true stress‐strain measurement is needed, this is a much simpler test method than other methods previously suggested. In addition, the use of the natural drawing ratio (NDR) as ESCR ranking indicator is examined. Results show that NDR can also be employed as a strain rate‐independent indicator of ESCR of HDPE. The test proposed herein is practical, simple and precise, and hence a more reliable indicator of ESCR performance of HDPE.     

Quadrupole mass filter operation under the influence of magnetic field

This work demonstrates resolution enhancement of a quadrupole mass filter (QMF) under the influence of a static magnetic field. Generally, QMF resolution can be improved by increasing the number of rf cycles an ion experiences when passing through the mass filter. In order to improve the resolution, the dimensions of the QMF or the operating parameters need to be changed. However, geometric modifications to improve performance increase the manufacturing cost and usually the size of the instrument. By applying a magnetic field, a low‐cost, small footprint instrument with reduced power requirements can be realized. Significant improvement in QMF resolution was observed experimentally for certain magnetic field conditions, and these have been explained in terms of our theoretical model developed at the University of Liverpool. This model is capable of accurate simulation of spectra allowing the user to specify different values of mass spectrometer dimensions and applied input signals. The model predicts enhanced instrument resolution R>26 000 for a CO₂ and N₂ mixture with a 200‐mm long mass filter operating in stability zone 3 via application of an axial magnetic field. Copyright © 2013 John Wiley & Sons, Ltd.     

应用多接收器电感耦合等离子体质谱法测定海洋碳酸盐中稳定铅同位素组成

研究了多接收器电感耦合等离子体质谱仪(MC-ICP MS)测定铅同位素比值时,影响测试结果准确度和精密度的主要因素及其优化过程。在优化条件下,10 h内连续30次测定4 ng/mL NIST SRM 981同位素标准溶液铅同位素比值,获得208Pb/206Pb、207Pb/206Pb和206Pb/204Pb相对标准偏差(RSDs)分别为0.005%、0.004%和0.054%。长期监测208Pb/206Pb、207Pb/206Pb和206Pb/204Pb,标准偏差(2SDs)分别为0.000 06、0.000 05和0.006 7。采用NEPTUNE MC-ICP MS法测定了低铅海洋碳酸盐样品中稳定铅的同位素比值,并对南海橙黄滨珊瑚(Porites lutea)和库氏砗磲(Tridacna gigas)进行了分析,得到全流程空白为8～10 pg,重复样误差优于0.1%。经0.50 mol/L HNO3洗脱之后,得到海南珊瑚样品中208Pb/206Pb、207Pb/206Pb的比值分别为2.086 2±0.001 5、0.849 90±0.001 47(n=16);海南砗磲样品中208Pb/206Pb、207Pb/206Pb的比值分别为2.116 9±0.004 2、0.864 81±0.001 62(n=9)。进一步考察了南海海洋碳酸盐中204Pb的同位素比值。分析结果表明,南海海洋碳酸盐中稳定铅同位素比值与中国气溶胶、珠江三角洲大气沉降、黄土及南海海底玄武岩等具有很好的相关性。方法适用于复杂基体高钙低铅的海洋碳酸盐样品中铅同位素比值的分析。     

Dephosphorylation of intact glycoprotein to greatly improve digestion efficiency coupled with matrix-assisted laser desorption/ionization–Fourier transform ion cyclotron resonance mass spectrometric analysis

Sialylation is essential for a variety of cellular functions. Herein, we used bovine fetuin with three potential N-linked glycosylation sites containing complex-type glycan structures, four potential O-linked glycosylation sites and six potential phosphorylation sites as a model compound to develop a highly-efficient digestion strategy for sialylated glycoproteins and efficient enrichment strategy for sialylated glycopeptides using titanium dioxide. The former according to the process of alkaline phosphatase digestion followed by tryptic digestion and then proteinase K digestion could greatly improve the enzymatic efficiency on fetuin, and the latter could obviously enhance the enrichment efficiency for multisialylated glycopeptides using phosphoric acid solution as elution buffer. The mass spectra of the enriched glycopeptides derived from fetuin reveal that several series of the ion clusters with mass difference of 291 Da correspond to the presence of multisialylated glycopeptides. In addition, the approach was applied to characterize the sialylated status of α2-macroglobulin and transferrin, respectively, from the sera of healthy subjects and sex- and age-matched patients with thyroid cancer, and their spectra indicate that the change in the amount of the glycoforms containing different number of sialic acid (SA) residues from one glycosylation site may be used to differentiate between healthy subjects and cancer cases.     

Anisotropic studies of multi-wall carbon nanotube (MWCNT)-filled natural rubber (NR) and nitrile rubber (NBR) blends

50/50 NR/NBR blends with various MWCNT loadings were prepared by mixing with MWCNT/NR masterbatches on a two-roll mill and sheeted off at the smallest nip gap. Then, the effect of milling direction, machine direction (MD) and transverse direction (TD), on the mechanical and electrical properties of the blends was elucidated. Dichroic ratio and SEM results confirmed that most of the MWCNTs were aligned along MD when MWCNT was less than 4 phr, and the number of agglomerates increased when MWCNT was more than 4 phr. Additionally, anisotropic properties were clearly observed when 4 phr MWCNT was loaded. At 4 phr MWCNT, 100% modulus and tensile strength in the MD were about 1.5 and 1.3 times higher than those in the TD, respectively. Moreover, electrical conductivity in the MD was superior to that in the TD by about 3 orders of magnitude. Results from dynamic mechanical tests also showed that the maximum tan δ in the MD sample was lower than that in the corresponding TD sample. In addition, the storage modulus at 30 °C for the MD sample containing 4 phr MWCNT was 1.15 higher than that of the corresponding TD sample. This stronger reinforcement efficiency resulted from the combination of the greater alignment and dispersion of most MWCNTs in the MD sample.     

Swelling and Network Parameters of 1-Hexadecene-Co-Trimethylolpropane Distearate Monoacrylate Sorbers

Linear and crosslinked copolymers with different compositions of 1-hexadecene and trimethylolpropane distearate monoacrylate monomers were synthesized and evaluated for oil-absorbency application. Different concentrations of ethylene glycol diacrylate (EGDA) and ethylene glycol dimethacrylate (EGDMA) crosslinkers were used. The concentration of both crosslinkers was varied from 0.5% to 2%. Copolymer compositions were determined from ¹H NMR spectroscopy. Monomer reactivity ratios were calculated using Fineman-Ross and Kelen-Tudos techniques at low conversions. The oil absorbency and swelling rate constant were measured and influenced mainly by the degree of crosslinking and the hydrophobicity of copolymer units. The final equilibrium oil content, volume fraction of polymer and swelling capacity were determined at 298 K. The effective crosslinking density V_e, theoretical crosslink density V_t, the average molecular weight between the crosslinks M_c and the polymer-toluene interaction parameter χ were determined from swelling measurements. The efficiencies of EGDA and EGDMA crosslinking agents toward copolymers were determined.     

Characterization of Chitosan/Alginate Self-Assembled Nanoparticles as a Protein Carrier

The aim of this study was to evaluate the effect of the polymeric ratios on the characteristics of chitosan/alginate (ch/alg) self-assembled nanoparticles and their potential as protein delivery vehicle. The nanoparticles were prepared using proper mixing of polymers in presence or absence of bovine serum albumin (BSA) as a protein model. Three formulations of nanoparticles comprising ch/alg ratios of 2:1, 1:1, and 1:2 were prepared. Size, shape and zeta potential of the formulations were studied by scanning electron microscopy (SEM) and nanosizer instruments. FTIR, and differential scanning calorimetery (DSC) studies were performed to investigate polymer-polymer or polymer-protein interactions. Release profiles and entrapment efficiencies of the nanoparticles were determined by calorimetric technique using appropriate techniques. Entrapment efficiency was 70% for ch/alg ratio of 1:1, 65% for 1:2, and 60% for 2:1. The z-average size of the nanoparticles were 403, 205, and 318 nm for ch/alg ratios of 2:1, 1:1, and 1:2, respectively. Average zeta potentials were ?47, +15, ?25 mV for 2:1, 1:1, and 1:2 as well. Considering the favorable features required for protein delivery systems, ch/alg (1:1) due to its smallest size, highest loading, and most homogenous shape was regarded as the best ratio.