PHOTO-INDUCED GRAFT POLYMERIZATION OF ACRYLAMIDE ON POLYPROPYLENE MEMBRANE SURFACE IN THE PRESENCE OF DIBENZYL TRITHIOCARBONATE

Ultraviolet （UV）-induced graft polymerization of acrylamide （AAm） on polypropylene substrates was successfully conducted using dibenzyl trithiocarbonate （DBTTC） as photoinitiator. It was confirmed by chemical analysis and surface morphology observation with attenuated total reflectance Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and scanning electron microscopy. A possible mechanism for this graft process was presented, which suggested that, under UV irradiation, the C： S bond in DBTTC could split and abstract a hydrogen from the polypropylene surface and a surface free radical was then formed, and initiated the graft polymerization of AAm.     

STUDIES ON THE INITIATION MECHANISM OF CERIC ION AND ACETYLACETONE REDOX SYSTEM IN VINYL POLYMERIZATION

The initiation mechanism of acrylamide (AAM)polymerization using ceric ion/acetylacetone system as an initiator has been studied. The redox polymerization was revealed by the low value of overall activation energy of AAm polymerization. The structure of free radicals formed from above-mentioned initiation sytem were detected by radical trapping and ESR spectra techniques and the end groups of polymers obtained were determined by FT-IR spectra analysis method. Based on these results the initiation mechanism is proposed.     

Acrylamide as cosurfactant and hydrotrope in the pseudoternary Span 80-Tween 85/isopar M/water emulsion/microemulsion forming system

The aim of this study was to investigate the effects of acrylamide on emulsification of the pseudoternary Span 80-Tween 85/isopar M/water system at 40 °C. It was revealed that acrylamide could act as a surface-active agent to decrease the isopar M/water interfacial tension, and as a hydrotrope to increase the aqueous solubility of Tween 85, and further remarkably influence the emulsification of the investigated pseudoternary Span 80-Tween 85/isopar M/water system. The surface-active role of acrylamide could reduce the minimal weight fraction of the mixture of Span 80 and Tween 85 in pseudoternary systems (X_ST) to form stable water-in-oil (W/O) emulsions when the weight fraction of acrylamide in the aqueous domain (X_AM) is below 0.1; while its hydrotropic role at high X_AM levels (>0.1) could drive more Tween 85 molecules to transfer into aqueous phase and slightly improved the minimal X_ST to form stable W/O emulsions, as compared to that of X_AM at 0.1. Moreover, under a given X_ST, the mean diameter of the droplet size distribution of the W/O emulsion remarkably decreased with the increase in X_AM; while the smaller droplets in the W/O emulsion systems at higher level of X_AM still coalesced rapidly when the compositions of the emulsion was slightly above the visually determined boundary between non-emulsion and stable emulsion regions.     

Diffusion coefficients of lithium chloride and potassium chloride in hydrogel membranes derived from acrylamide

Diffusion of non-associated electrolytes (potassium chloride and lithium chloride) in concentrated aqueous solutions (0.1-1.0 mol dm⁻³) has been studied in hydrogels derived from acrylamide and methyl methacrylate to study the mechanism of electrolyte transport. The preparation of two gels with different monomer ratio compositions resulted in obtaining membranes of substantially different hydrophilic character with polymer fractions of 0.3 and 0.5.Cukier hydrodynamic model was applied to explain the dependence of the diffusion coefficients of KCl and LiCl on the electrolyte concentration in hydrogel obtained experimentally. It was shown that the increase of the diffusion coefficients is accompanied with a decrease of the mean distance of approach of the ions. This can be explained by the formation of ion-pairs, resulting in a further contribution to diffusion once there is a decrease in the hydrodynamic resistance of the medium to the diffusing particles. Parameters, which characterise such a behaviour quantitatively, are different for different electrolytes and depend on water content in the gel.     

Grafting of acrylamide onto cellulosic fibers via dielectric-barrier discharge

Fully bleached kraft pulp (BKP) and thermomechanical pulp (TMP) fibers were grafted with acrylamide via dielectric-barrier discharge treatment at various treatment dosages. The results indicate that increased dielectric-barrier discharge treatment leads to the increased polymerization and incorporation of acrylamide onto fiber surfaces. Greater incorporation of poly(acrylamide) occurs on the BKP fibers than the TMP at the same treatment conditions. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) and scanning electron microscopy (SEM) indicate that dielectric-barrier discharge initiated modifications to fiber surface topo-chemistry occur across the fiber such that the sheet is randomly peppered with modified areas; however, it occurs in patches on individual fibers as opposed to occurring as an evenly distributed thin film. SEM and elemental analysis also showed that the incorporation of acrylamide onto the fiber surface increases with increased treatment dosages.     

Diffusion coefficients of sodium dodecyl sulfate in water swollen cross-linked polyacrylamide membranes

Diffusion of aqueous sodium dodecyl sulfate (SDS) across cross-linked polyacrylamide hydrogel membranes has been studied by electrical conductivity measurements. Initial rapid sorption of SDS (as unimer) into the membranes is observed. The effect of SDS concentration, and of cross-linker fraction on the degree of swelling of the gels is studied and associated with binding of the surfactant to the polymer, with surface bound water suggested to be involved in these interactions. Below the surfactant critical micelle concentration, volume collapse of less cross-linked membranes is observed, and associated with aggregate formation. Fluorescence measurements using pyrene as a probe show that micellar aggregates do not diffuse through the membrane, and only overall unimer diffusion is observed. The effect of cross-linking on the diffusion process is discussed.     

Analysis of acrylamide in different foodstuffs using liquid chromatography–tandem mass spectrometry and gas chromatography–tandem mass spectrometry

Acrylamide levels over a wide range of different food products were analysed using both liquid chromatography–tandem mass spectrometry (HPLC–MS–MS) and gas chromatography–tandem mass spectrometry (GC–MS–MS). Two different sample preparation methods for HPLC–MS–MS analysis were developed and optimised with respect to a high sample throughput on the one hand, and a robust and reliable analysis of difficult matrices on the other hand. The first method is applicable to various foods like potato chips, French fries, cereals, bread, and roasted coffee, allowing the analysis of up to 60 samples per technician and day. The second preparation method is not as simple and fast but enables analysis of difficult matrices like cacao, soluble coffee, molasses, or malt. In addition, this method produces extracts which are also well suited for GC–MS–MS analysis. GC–MS–MS has proven to be a sensitive and selective method offering two transitions for acrylamide even at low levels up to 1 μg kg⁻¹. For the respective methods the repeatability (n=10), given as coefficient of variation, ranged from 3% (acrylamide content of 550 μg kg⁻¹) to 12% (acrylamide content of 8 μg kg⁻¹) depending on the food matrix. The repeatability (n=3) for different food samples spiked with acrylamide (5–1500 μg kg⁻¹) ranged from 1 to 20% depending on the spiking level and the food matrix. The limit of quantification (referred to a signal-to-noise ratio of 9:1) was 30 μg kg⁻¹ for HPLC–MS–MS and 5 μg kg⁻¹ for GC–MS–MS. It could be demonstrated that measurement uncertainties were not only a result of analytical variability but also of inhomogeneity and stability of the acrylamide in food.     

近年来丙烯酰胺聚合反应的发展

本文论述了丙烯酰胺８０年代后期在聚合反应方面的研究状况，着重对引发体系、聚合技术的变化及有关的新产品作了概述。     

High‐efficiency sample preparation approach to determine acrylamide levels in high‐fat foods

An improved sample preparation method was developed to enhance acrylamide recovery in high‐fat foods. Prior to concentration, distilled deionized water was added to protect acrylamide from degradation, resulting in a higher acrylamide recovery rate from fried potato chips. A Chrome‐Matrix C₁₈ column (2.6 μm, 2.1 × 100 mm) was used for the first time to analyze acrylamide levels using ultra high performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry, displaying good separation of acrylamide from interference. A solid‐phase extraction procedure was avoided, and an average recovery of >89.00% was achieved from different food matrices for three different acrylamide spiking levels. Good reproducibility was observed, with an intraday relative standard deviation of 0.04–2.38%, and an interday relative standard deviation of 2.34–3.26%. Thus, combining the improved sample preparation method for acrylamide analysis with the separation on a Chrome‐Matrix C₁₈ column (2.6 μm, 2.1 × 100 mm) using ultra high performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry is highly useful for analyzing acrylamide levels in complex food matrices.     

Photopolymerization of water-soluble acrylic monomers induced by colloidal CdS and Cd x Zn1 − x S nanoparticles

Photocatalytic activity of CdS and Cd _x Zn_1−x S nanoparticles in the polymerization of acrylamide and acrylic acid in aqueous solutions has been found. It has been shown that the most probable way of the photogeneration of primary radicals is the reduction of an adsorbed monomer by the conduction band electrons of the semiconductor nanoparticles, a monomer oxidation by the valence band holes and atomic hydrogen addition to a monomer being complementary photoinitiation routes. A correlation between the composition of Cd_xZn_1-xS nanoparticles and their photocatalytic activity in the acrylamide polymerization has been established. It has been shown that an increase in the quantum yield of the photopolymerization in a sequence СdS < Cd_0.75Zn_0.25S < CdS_0.5Zn_0.5S < Cd_0.3Zn_0.7S originates from a concurrent increase of the conduction band potential of the semiconductor nanoparticles. A kinetic equation of the photocatalytic acrylamide polymerization has been derived. Quantum yields of the photoinitiation have been found to be as small as 10⁻⁴ to 10⁻³.