M/N ratio

Siloxane Polymers. The synthesis of the ferrocene-modified siloxane polymers (A - E) has been described previously (25,27,32). Briefly, the methyl(2-ferrocenylethyl)-siloxane polymers were prepared by the hydrosilylation of vinylferrocene with the methylhydrosiloxane homopolymer or the methylhydrosiloxane-dimethylsiloxane copolymers (m n ratios of 1 1, 1 2, and 1 7.5 see Figure 1) in the presence of chloroplatinic acid as a catalyst. The methyl(9-ferrocenylnonyl)siloxane-dimethylsiloxane (1 2) copolymer was prepared via hydrosilylation of 9-ferrocenyl-l-nonene with the methylhydrosiloxane-dimethylsiloxane (1 2) copolymer. The molecular weight range of these ferrocene-modified siloxane polymers is approximately 5,000-10,000. Purification of the polymers was achieved by reprecipitation from chloroform solution, via dropwise... 

Lind bases his cluster-ion theory on these results with alpha particles. Each ion attaches one or more neutral molecules of the reacting substances and when the ions are neutralized all the molecules involved in the two clusters undergo chemical reaction. The M/N ratio gives a measure of the number of neutral molecules... 

A ratio of 4 molecules of carbon dioxide to each ion pair is predicted on the basis of this theory. By direct experiment the M/N ratio is found to be 3.9 to 4.4. In other reactions, as in the polymerization of acetylene a cluster of twenty molecules is assumed in order to account for the experimentally determined M/N ratio. The cluster ion offers a satisfactory explanation of many radiochemical reactions but the size of the cluster is assigned rather arbitrarily, and there may be other ways of accounting for the experimental facts. 

The ratio of ferrocene-modified siloxane subunits to unsubstituted siloxane subunits rrv.n ratio) was varied as was the length (a ) of the alkyl side chain onto which the ferrocene moiety was attached as shown in Fig. 3.3. The electrode containing co-polymer with m n ratio of 1 1 or 1 2 was the more efficient electron relay systems. The ferrocene-modified homopolymer on the other hand loses flexibility due to steric hindrance caused by the side chain substitution by ferrocene, preventing efficient electron transfer from the enzyme to the electrode. The length of the alkyl side chain onto which the ferrocene moiety is attached was also found to influence the electron transfer efficiency of the electron relay system. Maximal current density was measured... 

Fig. 3.8. (a) A Structure of the hydroquinone-containing poly(siloxane). B Structure of the hydroquinone-containing poly(acrylonitrile-ethylene). The m n ratio is approximately 1 2 for both systems. Reprinted with permission from [10]. (b) Structure of the polyCether amine quinone) polymers. Reprinted with permission from [15], 1994 American Chemicad Society. 

A polystyrene/polyZ-butyl methacrylate (PS/PtBMA) di-block copolymer was previously synthesized for the polymer brush studies. The molecular weight of the copolymer is approximately 50,000 g/mol with the m n ratio approximately 1 1. The chemical structure of the di-block copolymer appears in Figure 3.2-1. 

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