Dehydration polymerization

It is used as a catalyst in esterification, dehydration, polymerization and alkylation reactions. Converted by e.g., ihionyl chloride, to melhanesulphonyl chloride (mesyl chloride) which is useful for characterizing alcohols, amines, etc. as melhanesulphonyl (mesyl) derivatives. 

Figure 19. High-resolution MAS solid-state 1SC-NMR spectra of the cracked products of the dehydration-polymerization products of 2-lsC-isopropanol. (Reproduced with permission from ref. 68. Copyright 1985 Elsevier.)...

The conversion of reactants is illustrated by the dehydration-polymerization of 2-isopropanol adsorbed on K- and Cs-ZSM-5 zeolites as followed by 1JC-NMR. On the other hand, the polymerization of ethylene shows a clear-cut difference between three-dimensional channel systems (ZSM-5 and ZSM-11) able to promote the molecular traffic of reactants and on one-dimensional channel systems (ZSM-48) where some unreacted ethylene is still detected after polymerization. 

Normally, dehydration reactions are conducted in nonaqueous media. However, as one product of the dehydration (water) is in equilibrium with the starting materials, the water present as solvent will deter the dehydration from proceeding in an aqueous medium, on the basis of the Law of Mass Action. A lipase-mediated catalysis will, nevertheless, allow the dehydration polymerization of a dicarboxyiic acid and glycol to occur in water [72,73], thereby providing a new aspect to organic chemistry. 

A dehydration polymerization of dicarhoxylic acids and glycols took place by lipase catalyst even in water (95,96). This catalysis of lipase is quite specific since a dehydration reaction in an aqueous solution is generally disfavored by water, which is in equilibrium with starting materials because of the law of mass action. Hydrophobic monomer combinations gave the polyesters in good yields. 

It is interesting that macrolides, such as UDL and DDL, are polymerized by Upase in an aqueous medium. That is, Kobayashi and Uyama et aL presented the polyester synthesis by dehydration polymerization in aqueous medium using lipase. This is due to the hydrophobic nature of the catalytic domain of the lipase as well as hydrophobic nature of the macroUde [10]. 

The enzymatic synthesis of a telechelic polyester having a hydroxy group, a prepolymer of polyurethane, at both ends was reported [38]. The lipase CA-catalyzed polymerization of adipic acid with an excess of 1,4-butanediol was performed imder reduced pressure. The content of water formed by dehydration polymerization greatly affected the enzyme activity and polymerization rates. 

For non-Si02 supported vanadia catalysts, the simultaneous presence of dehydrated polymeric surface VO4 species and dehydrated isolated surface VO4 species is detected by in situ UV-Vis as a shift in the charge transfer transition... 

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