1.3.5- Trioxane radiation polymerization

The Polymerization-Crystallization Stage in the (Co)polymerizations of 1,3,5-Trioxane Radiation-Initiated Solid-State Polymerization of 1,3,5-Trioxane Properties of Poly(oxymethylene)... 

Okamura, S., Hayashi, K., and Nishii, N. (1962) Polymer crystals obtained by radiation polymerization of trioxane in solid state./. Polymer Sci., 60, —26. 

The solubility of polyoxymethylene is very poor so that the ring-opening polymerization of 1,3,5-trioxane proceeds heterogeneously both in bulk (melt) and in solution. 1,3,5-Trioxane can also be readily polymerized in the solid state this polymerization can be initiated both by high-energy radiation and by cationic initiators (see Example 3-24). 

When the monomer is a solvent both of the corresponding polymer and of the initiator, polymerization proceeds in a single phase it is homogeneous. The dissolving role of the monomer may sometimes be taken over by the solvent. Of course, homogeneous polymerizations are not limited to the liquid phase. Solid pure trioxane can be transformed into a highly crystalline polymer by y radiation. 

It is important to recognize that in such cases the rate law of polymerization as obtained by determination of the polymer yield reflects the growth of morphological entities rather then the formation of molecular intermediates and may be determined by the rate of nucleation and by the rate of diffusion of the monomer molecules across the interphase between monomer and polymer lattice. This is well established in the somewhat related case of radiation-induced polymerization of crystalline trioxane (27, 28). 

Radiation-induced Solid-state (RISS) Polymerization of 1,3,5-Trioxane... 

The cationic polymerization of trioxane can be initiated by protonic acids, complexes of organic acids with inorganic salts, and compounds that form cations. These initiators differ from each other in activity and in the influence on terminations and on side reactions. Trioxane can also be polymerized by high-energy radiation. In addition, polymerizations of trioxane can be carried out in the solid phase, in the melt, in the gas phase, in suspension, and in solution. Some of these... 

Crystalline polymers were obtained by the radiation-induced polymerization of various cyclic compounds in the solid state " . Especially the cyclic oligomers of formaldehyde (CHjO), i.e., trioxane (TOX) (n = 3), tetroxocane (TeOX) (n = 4), pentoxaiK (P OX) (n = 5), and hexoxane (HeOX) (n = 6), easily produce polyfoxy-methylene (POM) by radiation-induced polymerization in the solid state... 

The polymerization of trioxane in the crystalline state is a well-known example of radiation-induced solid-state polymerization In the polymerization of crystalline monomers, the topotactical conditions are very important and polymerization is possible only for a very few monomers. The situation is completely different for... 

A unique feature of high-energy-radiation apphcations relates to solid-state polymerizations [27-31]. In this case, a catalyst is not required and the irradiations can be performed at deliberately chosen temperatures, because the absorption of radiation is temperature-independent. Of particular interest in this context are compounds such as trioxane, hexamethylcyclotrisiloxane, P-propiolactone and diketene, all of which polymerize readily in the solid state but slowly, or not at ah, in the hquid state. Other compounds such as styrene, acrylonitrile and formaldehyde polymerize faster in the crystalline state than in the liquid state just above the melting point Compounds that undergo solid-state polymerization upon y-hradiation are listed in Table 5.1. In contrast, vinyl chloride, vinyl acetate and methyl methacrylate do not polymerize in the solid state. 

Commonly, a significant conversion of sohd monomers is observed at temperatures close to the melting point. For example, solid trioxane is not converted at 25 °C but polymerizes at 55 °C. Above this temperature, the conversion increases in proportion to the dose of radiation absorbed (Figure 5.5). 

A number of ethylenic monomers and cyclic monomers undergo chain polymerization in the solid state when exposed to high-energy radiation (e.g. y-radiation). Examples include acrylamide, acrylic acid, acrylonitrile, vinyl acetate, styrene, 1,3,5-trioxane, propriolactone and hexamethylcyclo-trisiloxane. These polymerizations may involve free-radical and/or ionic species, but in most cases the precise mechanisms operating are not known. 

Activation Energy of Polymerization (kJ/mol) Of radiation induced trioxane ... 

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