Trioxane and trithietane

Trioxane is the cyclic trimer of formaldehyde and it can be polymerized to yield polyoxymethylene having the same structure as polyformaldehyde. Polymerization has been carried out with or without catalyst in the liquid, solid, and sublimed states. All polymerizations appear to proceed by a cationic mechanism and the usual type of cationic initiators are effective [122,138—141]. The structure of the cationic chain ends is not clear and two types of props ating centres have been proposed [142], namely, tertiary oxonium ions and carbenium ions. Their propagation reactions are 

Recently, some kinetic coefficients have been determined in electro-chemically initiated polymerizations [144]. Trioxane, dissolved in three different solvents (acetonitrile, benzonitrile, and nitrobenzene) with tetra-butylammonium perchlorate as background electrolyte, was polymerized in the anodic compartment. Definite solvent dependence was shown. When the current was turned off, polymerization in acetonitrile ceased in 

In some recent studies [145] of the kinetics of the polymerization of trioxane initiated by BF3. Et2 0 and by FeCla. PhjCCl, the course of the polymerization appeared to be quite complex. Rate and equilibrium parameters were evaluated and their significance was discussed. The number of active centres was not determined independently, so again these results must be considered preliminary and will not be quoted here. 

In contrast to the polymerization of trioxane which has been studied a great deal, few studies of the polymerization of trithietane have been reported [36]. It has been polymerized using many of the same initiators as trioxane and the mechanism is probably just as complex. As far as we know kinetic studies have not been published. 

A large number of copolymers of cyclic ethers, cyclic sulphides and cyclic formals have been prepared. Many cyclic compounds that will not homopolymerize do copolymerize readily [7, 146,147]. Some cyclic compounds will copolymerize with lactones, cyclic anhydrides, or vinyl monomers. Very many commercially important materials have resulted from these copolymerizations. 

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