Fundamental considerations on the mechanism of copolymerization of trioxane and ethylene oxide initiated with boron trifluoride dibutyl etheratePresented at the 5th International Symposium on Cationic and Ionic Polymerizations, Kyoto, Japan April 15-18, 1980.

0360-6376

Physics ; Polymer and Materials Science

Wiley InterScience Backfile Collection 1832-2000

Chemistry and Pharmacology

A comprehensive mechanistic scheme that accounts for the unique experimental features of the copolymerization of bulk trioxane (TOX) with 2% (wt/wt) ethylene oxide (EO) was developed. The formation of the primary initiating species is shown as the diffusion-limited reaction of trace water with boron triflouride dibutyletherate [BF3O(Bu)2] to form a Bronsted acid. This acid complexes principally with the more basic EO and partly with the less basic TOX. The acid-complexed TOX depolymerizes to formaldehyde which can react with acid-complexed EO in an insertion reaction to form an acid-complexed dioxolane. Further insertion of formaldehyde yields an acid-complexed trioxepane. This sequence is generalized into a propagation scheme that involves propagation by expansion and ring opening. Displacement of complexed dioxolane and trioxepane can occur in the event that the more basic EO attacks the oxonium-active site at the reactive position outside the oxonium ring. These displacement reactions account for the observation of formation of dioxolane and trioxepane. The polymerization of formaldehyde is not considered significant until all EO has been consumed. During the latter stages of polymerization, cyclic oxonium-active sites are transformed into oxocarbenium sites that are stabilized by complexation with the polymer chain. This complexation is the origin of the phenomena of transacetalization and hydride transfer.

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