Siloxane groupings, analysis

Table II provides a summary of the results on the characteristics of aminopropyl terminated poly(dimethyl-diphenyl)-siloxane oligomers synthesized. These reactions were conducted in bulk at 160°C with K0H as the initiator. As can be seen from Table II the stoichiometric number average molecular weights sought and obtained are in very good agreement. The level of diphenylsiloxane incorporation was determined by UV spectroscopy. There is no absorption of dimethylsiloxane backbone in the spectral range of 240 to 280 nm. On the other hand, phenyl groups absorb very strongly over these wavelengths (Figure 3). For quantitative analysis we have used the absorption peak at 270 nm as the reference.

Kohn, E. "High Performance Size Exclusion Chromatography (IX) Bulk and Component Analysis of Silanol Groups in Polydimethyl-siloxanes" Mason Hanger - Silas Mason Co. Inc., Amarillo,... 

So interpretation of the B-H vibration bands confirmed the different reactions of diborane with the hydroxylic surface groups put forward by Shapiro and Weiss.35,36,49 In addition the infrared analysis of the modified surface revealed (1) the reaction of B2H6 with siloxanes, explaining the low hydrolysis ratios found under certain reaction conditions and (2) the equilibration reaction existing between B2H6 in the gas phase and the monodentate groups formed through reaction of BH3 with a surface hydroxyl. 

As was pointed out above, B2H6 reacts, apart from the hydroxyl groups also with the siloxane sites in a chemical way. The reaction consists in the formation of a Si-H group and a surface SiOBH2 group, as shown in reaction (O). Mashenko48 was the first to report this reaction, based on infrared analysis of the modified surface. A band at 2300 cm1 was found which was clearly no typical =B-H band. The... 

Gorton and coworkers have been particularly active in this field and produced an excellent review of the methods and approaches used for the successful chemical modification of electrodes for NADH oxidation [33]. They concentrated mainly on the adsorption onto electrode surfaces of mediators which are known to oxidise NADH in solution. The resulting systems were based on phenazines [34], phenoxazines [35, 36] and pheno-thiazines [32]. To date, this approach has produced some of the most successful electrodes for NADH oxidation. However, attempts to use similar mediators attached to poly(siloxane) films at electrode surfaces have proved less successful. Kinetic analysis of the results indicates that this is because of the slow charge transfer between the redox centres within the film so that the catalytic oxidation of NADH is restricted to a thin layer nearest the electrode surface [37, 38]. This illustrates the importance of a charge transfer between mediator groups in polymer modified electrodes. 

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