Poly catalytic mechanism

An important example for the snrface catalytic mechanism is the catalytic 0-xidation of DNA at pyrolytic graphite electrode modified with adsorbed poly(4-vinilpyridine) (PVP) with attached Rn(bpy)2 (bpy = 2,2 -bipyridyl) [109]. At low... 

The first step for the synthesis of a melt spinnable polysilane is the alkoxylation and distillation of the residue (Figure 1). 1,2-dimethyltetramethoxydisilane and 1,1,2-trimethyltrimethoxydisilane are mixed in a special ratio and a poly silane will be obtained by a catalytic redistribution reaction. Catalysts for this reaction are alkali alkoxides like sodium methoxylate. Phenylmethoxydisilanes [22] or phenylchloride are used as additives. A mixture of methyltrimethoxysilane and dimethyldimethoxy-silane distils off as a byproduct of the redistribution reaction. Figure 2 shows the mechanism of the catalytic redistribution. 

Although there is evidence that all poly(HA) depolymerases cleave the polyesters by the same mechanism (catalytic triad), the poly(3HO) depolymerase differs considerably from poly(HASCL) depolymerases in terms of primary sequence and polymer-binding. This might be due to different approaches of these enzymes to get access to the polymers reflecting the distinctive physicochemical properties of poly(HASCL) and poly(HMCLA) rather than coevolution. 

Otton, J., Ratton, S., Vasnev, V. A., Markova, G. D., Nametov, K. M., Bakhmutov, V. I., Komarova, L. I. Vinogradova, S. V. and Korshak, V. V., Investigation of the formation of poly(ethylene terephthalate) with model molecules Kinetics and mechanisms of the catalytic esterification and alcoholysis reactions II. Catalysis by metallic derivatives (monofunctional reactants), J. Polym. Sci., Polym. Chem. Ed., 26, 2199-2224 (1988). 

A few years later, Baba reported a more comprehensive description of the coupling reaction of oxetane and C02 catalyzed by organotin iodides and Lewis bases as catalysts [60]. It was shown in this instance, that the choice of Lewis base which coordinated to the organotin iodides affected the catalytic activity and selectivity, that is, poly(TMC) and/or trimethylene carbonate. Whilst complexes with Bu3P yielded polycarbonate, the combination of Bu3SnI with Bu3P=0 yielded TMC exclusively in good yields. A reaction mechanism, as proposed by Baba and coworkers, is illustrated in Scheme 8.5. 

The molecular weight values of poly(TMC) obtained from oxetane and C02 in the presence of a (salen)CrCl/n-Bu4NN3 catalyst system were generally lower than the theoretical values (Mn = 11050 Mn (theoretical) = 85 000). This situation was most likely due to a chain transfer mechanism arising from the presence of trace amounts of water in the system. However, when the catalytic runs were carried out under rigorously anhydrous conditions, the molecular weights more closely tracked the predicted values. 

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