Silver/ions with polymers

Steed and co-workers synthesized pyridylurea ligand 36b that formed coordination polymer using pyridyl groups and silver ions. Interestingly, polymer formation could be influenced by the H-bonding of the urea units with counter anions (NOs or BF4 ) [75]. Ligand 36a has a shortened ethylene chain. Three molecules could complex two nitrates to form a Borromean weave via a total of 12 H-bonds (N—O = 2.960-2.944 A) (Fig. 5.27) [76]. 

One approach to achieve this slower reaction is to complex the silver ion with an appropriate reagent such that the rate of silver-polymer formation should be retarded, and consequently its desired unimolecular decomposition will be more controlled. The crown ethers are species capable of such complexation. The rate of appearance of silver metal is an inverse function of the stability of the silver-crown ether complex. 

Brewis et al. used TOF-SIMS to determine the surface composition of hydrocarbon polymers after electrochemical pretreatment with nitric acid alone or in the presence of silver ions [58J. AgNO was generated by electrolysis of a 0.1 M solution of silver nitrate in 3.25 M nitric acid in the anode compartment of a... 

Electrochemical treatment of the polymers in nitric acid in the absence of silver ions was carried out at room temperature. Extent of oxidation was low for hd-PE and PP. It was not possible to directly compare the results with those obtained for oxidation in the presence of silver ions since different temperatures were used (room temperature versus 60°C). However, the spectra obtained after treatment indicated similar chemical effects for the two cases. For PS, it was possible to make direct comparisons because the same temperature was used for treatment in the presence and absence of silver ions. In that case, the overall degree of oxidation was lower. 

Auother uauostructuriug techuique shares some commou features with that described above and is shown in Fig. 36.3. A polymer-coated Pt ultramicroelectrode is used as the tip of a STM, and graphite is used as substrate. Ag atoms are deposited on the tip at underpotentials, so that approximately one atomic monolayer is deposited on the tip. After this, a first bias pulse is applied to the tip, causing the formation of a shallow pit. Then a second bias pulse with a smaller amplitude is applied to cause the desorption of silver from the tip. The silver ions desorbed diffuse aud migrate across the tip-sample gap aud deposit ou the high coordiuatiou sites preseut... 

The concept of dynamic silver clusters capable to transfer between molecules was also pointed out recently by Ras et al. for silver clusters prepared by photoactivation using PM A A as scaffold [20], Every specific initial ratio of silver ions to methacrylate unit, Ag+ MAA, results in distinct spectral bands (Fig. 12a, b). Thus, an initial ratio 0.5 1 gives an absorption band at 503 nm, whereas a ratio 3 1 gives a band at 530 nm. The shuttle effect was proven when for a given silver cluster solution with ratio 3 1 and absorption at 530 nm, a blue shift was achieved by the addition of pure PMAA. For instance if the added amount of polymer decreases the ratio Ag+ MAA from 3 1 to 0.5 1, the new optical band will match exactly with the band corresponding to a solution with initial ratio 0.5 1, that is 503 nm (Fig. 12c). The explanation given for this blue shift was the redistribution of the existent silver clusters in PMAA chains over the newly available PMAA chains, in other words that the clusters shuttle from partly clusters-filled chains to empty ones. 

The structure of 2AgN03-succinonitrile revealed the presence of complex cations, [AgNC(CH2)2CNAg]2+, and ionic nitrate ions.161 The Ag—N distances were 197 pm and the C—N bond distance was close to that expected for a triple bond (112 pm). In AgC104-2(adiponitrile) the structure was in the form of a two-dimensional polymer with the adiponitrile acting as a bridge between silver ions. The silver ion was tetrahedrally coordinated by four N atoms with Ag—N distances of —228 pm.163... 

To determine the effect of different polymerization conditions on the polymer endgroups produced, polymerizations were carried out using the standard bicarbonate buffer as well as other variations. Table V (13,16) shows that the use of the persulfate-bicarbonate combination with and without emulsifier gave latexes of final pH 7-8 with only sulfate groups. The addition of 10 5 silver ion gave a latex of pH 8.5, but with weak-acid groups, presumably because of oxidation of the sulfate groups. 

In applications where self-polishing is not possible, the combination of a microbe-repelling surface and a release system seems to be desirable. One example of a design for such a surface is shown in Fig. 8. The depicted coating is based on a hydrophilic polymer network that contains polyethyleneimine crosslinkers, which are capable of selectively taking up silver ions and acting as a template for silver nanoparticles [90], This reloadable co-network was surface-modified with PEG,... 

With AgC104, 1,5-hexadiene, 1,7-octadiene, and 1,9-decadiene form 3 2, 1 1, and 1 1 complexes, respectively (85a). The 1 1 complexes are considered (85a) to be coordination polymers while the 3 2 complex of 1,5-hexadiene has been shown (45a) to have chelated diene-silver ion entities connected through a bridging diene molecule to produce a distorted trigonal coordination about the metal. 

Free silver ions are the active components of antimicrobial silvers, and it has been shown that as little as one part per million of elemental silver in solution is an effective antimicrobial. Materials such as polymers, charcoal, and hydrocolloids when formulated with silver not only aid wound management and healing but also regulate its release into the wound environment and surrounding tissues. Silver ions kill micro-organisms by inhibiting cellular respiration and cellular function. " It is known that their mode of action is exerted by binding cysteine residues on the cell walls of yeasts such as C. albicans thereby... 

In a similar vein, Sakai, Takenaka and Torikai produced Nafion/metal microcomposites by reducing palladium, rhodium, platinum and silver ion-exchanged membranes with H, at high temperatures (100-300°C) (26). The affected metal clusters, distributed homogeneously, were about 50 A in size. As in Risen s work, a polymer matrix template effect appears to be operative. These systems were considered and evaluated within the context of gas separations technology. 

Fig. 1.3 Spectrum obtained using MALDI-TOF of a sample of polystyrene using a dithranol matrix with silver trifluoroacetate added. (The peak masses are from the polymer chains combined with a silver ion.)...

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