Polymer protection

The primary appHcation for barrier polymers is food and beverage packaging. Barrier polymers protect food from environmental factors that could compromise both taste and shelf life. They also help retain desirable flavors and aroma. Barrier polymers are also used for packaging medical products, agricultural products, cosmetics, and electronic components and in moldings, pipe, and tubing. 

Conventional filtration cannot be applied to the separation in purification of metal nanoparticles. If the metal nanoparticles are protected by polymer, however, the membrane filter, which can cut off the pol5mer with certain molecular weight, can be used to separate the polymer protected metal nanoparticles. Free metal nanoparticles which are not protected by polymer can pass through the membrane. Ion filter like cellulose can be used to separate ionic species from the reaction mixtures. 

Table 1 presents the mean diameters and standard deviations of Au nanoparticles synthesized at various TC BIP/Au molar ratios. Both the mean diameter and standard deviation decreased with an increase in the amount of the protective agent, TC BIP, which was also observed in the cases involving polymer-protected Pd [13], Pt [14,15], and Au nanoparticles [16]. For TC BIP (n = 8, 10, 12), Au nanoparticles smaller than 2nm could be... 

In the early work on the thermolysis of metal complexes for the synthesis of metal nanoparticles, the precursor carbonyl complex of transition metals, e.g., Co2(CO)8, in organic solvent functions as a metal source of nanoparticles and thermally decomposes in the presence of various polymers to afford polymer-protected metal nanoparticles under relatively mild conditions [1-3]. Particle sizes depend on the kind of polymers, ranging from 5 to >100 nm. The particle size distribution sometimes became wide. Other cobalt, iron [4], nickel [5], rhodium, iridium, rutheniuim, osmium, palladium, and platinum nanoparticles stabilized by polymers have been prepared by similar thermolysis procedures. Besides carbonyl complexes, palladium acetate, palladium acetylacetonate, and platinum acetylac-etonate were also used as a precursor complex in organic solvents like methyl-wo-butylketone [6-9]. These results proposed facile preparative method of metal nanoparticles. However, it may be considered that the size-regulated preparation of metal nanoparticles by thermolysis procedure should be conducted under the limited condition. 

Toshima N, Yonezawa T, Harada M, Asakuara K, Iwasawa Y (1990) The polymer-protected Pd-Pt bimetallic clusters having catalytic activity for selective hydrogenation of diene. Preparation and EXAFS investigation on the structure. Chem Lett 19 815-818... 

Harada M, Asakura K, Toshima N (1993) Catalytic activity and structural analysis of polymer-protected gold/palladium bimetallic clusters prepared by the successive reduction of hydrogen tetrachloroaurate(ffl) and palladium dichloride. J Phys Chem 97 5103-5114... 

Toshima, N. and Hirakawa, K., Polymer protected bimetallic nanocluster catalysts having core/shell structure for accelerated electron transfer in visible-light-induced hydrogen generation, Polymer J., 31, 1127, 1999. 

Lu, P. et al., Polymer-protected Ni/Pd bimetallic nano-clusters preparation, characterization and catalysis for Hydrogenation of Nitrobenzene, J. Phys. Chem. B, 103, 9673, 1999. 

Harada, M., Asakura K., and Toshima, N., Structural analysis of polymer-protected platinum/rhodium bimetallic clusters using extended x-ray absorption fine structure spectroscopy. Importance of microclusters for the formation of bimetallic clusters, J. Phys. Chem., 98, 2653, 1994. 

Toshima, N., Yonezawa, T., and Kushihashi, K., Polymer protected Pd-Pt bimetallic clusters preparation, catalytic properties and structural considerations, J. Chem. Soc. Faraday Trans., 89, 2537, 1993. 

Figure 17. Chronology of improvement in light transmission of glasses over periods of history leading to introduction of photonics technology in the information age. Polymer protection of glass surfaces is an essential present feature.

Extrusion coating has been developed to form thin polymer layers on flexible substrates like paper, paper board and metal foils in a high speed process (see Fig. 10) [27, 33, 34]. In combination with paper and paper board, the polymer protects the substrate from moisture, oil and fat. The polymer provides the welding properties to transform, e.g., the paper board/PE substrate into a paper cup, a liquid packaging board or a box for frozen food. 

Zhou Y, Itoh H, Uemura T, Naka K, Chujo Y (2002) Preparation, optical spectroscopy, and electrochemical studies of novel pi-conjugated polymer-protected stable PbS colloidal nanoparticles in a nonaqueous solution. Langmuir 18 5287-5292... 

Polymer-protected, monodisperse, nanoscale silver particles (Fig. 9.2.1c and d) have been obtained through spontaneous nucleation by the polyol process as follows (23). PVP (1-25 g) and AgNOj (50-3200 mg) were dissolved in EG (75 mL) at room temperature. Then the solution was heated up to 120°C at a constant... 

Ag-Pd Alloy Powders (7,27). Bimetallic colloids, namely, Ag-Pd and Au-Pt, can be obtained by the polyol process. The composition Ag7oPdx> is of particular interest to make the internal electrodes of multilayer ceramic capacitors (MLCC). Polymer-protected, monodisperse, nanoscale Ag70Pd30 particles have been obtained... 

Poiy(N-vinyl-2-pyrrolidone), PVP Bimetallic Pd-Pt particles Refluxing mixed solutions of palladium(II) chloride and hexachloroplatmicfTV) acid in ethanol-water (1 1, v/v) in the presence of PVP resulted in the formation of well-dispersed, stable, polymer-protected Pd-Pt particles 58... 

Tiopronin water soluble Au clusters have been described and their characterization by HRTEM and TGA has shown clusters of about 1.8 nm and a composition of Au2oi(Tiopronin)85 [65]. Polymer protected water soluble gold MPCs have also been synthesized using thiolated polyethyleneglycol (SH-PEG). H RTEM analysis displays a polydisperse population of clusters of 2.8 1 nm size and TGA results yields an average Au807(SH-PEG)98 composition [66]. 

Bemkop-Schntirch, A. and Arich, I. (1997). Synthesis and evaluation of a modified mucoad-hesive polymer protecting from a-chymotrypsin degradation. Int. J. Pharmaceut., 146, 247-254. 

Bemkop-Schntirch, A. and Gockel, N.C. (1997). Development and analysis of a polymer protecting from luminal enzymatic degradation of a—chymotrypsin. Drug Dev. Ind. Pharm., 23, 733-740. 

Kato, Y., Sugimoto, S., Shinohara, K., Tezuka, N., Kagotani, T. et al, Magnetic properties and microwave absorption properties of polymer-protected cobalt nanoparticles, Mater. Trans., JIM, 2002, 43, 406. 

Catalytic activities were shown to strongly depend on the Ni concentration and the molar ratio of borohydride to nickel170 180 182,183. Ni-B powders showed maximum activity when the NaBPLpNiCla ratio was 1.5 (the rate of the hydrogenation of cyclo-heptene was 4.3 x 10 3 mol g-atom Ni-1 s 1 303 K, 1 atm H2)184. When the synthesis, in contrast, was performed in the presence of PVP serving as a protective polymer, a threefold excess of NaBILj was required to achieve maximum activity (191 x 10 3 mol g-atom Ni-1 s-1)184. The polymer-protected sample proved to be especially effective in the hydrogenation of compounds with isopropenyl group (2-methyl-1-hexene and a-methylstyrene). 

High selectivity was also observed on a silica-supported Fe-Cu catalyst prepared by coprecipitation (333 K, 10 atm H2, ethanol)286 and over polymer-protected colloidal Pd-Pt cluster catalysts (303 K, 1 atm H2, ethanol)287,288. In contrast with the above observation, the activity of the bimetallic alloy was 1.4-3 times higher than that of the monometallic Pd cluster reaching the maximum activity at a composition of Pd/Pt = 4 1. 

Bernkop-Schniirch, A., and I. Apprich. 1997. Synthesis and evaluation of a modified mucoadhe-sive polymer protecting from a-chymotrypsinic degradation. Int J Pharm 146 247. 

There are two methods for the preparation of Cu-Ag double metal powder by replacement reaction. One is to react nano copper with silver nitrate solution directly in the existence of polymer protecting agent to produce Cu-Ag double metal powder, which, by TEM determination, appears usually in the form of twigs. In the other method, an Ag(NH i) + solution is used to replace the AgNOj solution to take part in the replacement reaction, and with the other conditions being the same as those in the former method, sphere particles can normally be obtained. The present study is aimed at the preparation of nano particles of sphere form, and so the second method is employed. 

Hirai. H., Wakabayashi, H. and Komiyama, M. (1983). Polymer-protected copper colloids as catalysis for selective hydration of acrylonitrile. Chemistry Letters. 1047-1050. 

Synthesis, properties, and applications of polymer-protected AuNPs have been reviewed by Shan and Tenhu and will not be covered in detail here.139 The basic motivation here is to better control the particle size and dispersity and to obtain robust materials avoiding metal loss during or after utilization of the polymeric material. 

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