Fundamental considerations on the mechanism of copolymerization of trioxane and ethylene oxide initiated with boron trifluoride dibutyl etherate

Abstract

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.

Interfacial reaction and its influence on phase morphology and impact properties of modified‐polyacetal/thermoplastic polyurethane blends

“…These results indicate that the generated protons during the chain transfer in each case, as shown in Scheme 1, were capable of reinitiation, and formed a hydroxyl end-group in POM. 25 …”

Specific phenomena during the copolymerization of trioxane and ethylene oxide

“…9) and Collins et al confirmed this mechanism and gave a more detailed discussion (Ref. 10). Previous work only shows the results of the reaction in the last stable zone.…”

Kinetics and mechanism of the cationic polymerization of trioxane. II. Consideration of hydride transfer

“…The hydride ion in the transfer reaction may be from the middle of an adjacent polymer molecule, from the end of the same molecule, or even from trioxane. 1,4,6 Rate constants for these transfer reactions rarely have been published.…”

“…A combination with oxygen atoms yields oxonium ions that then decompose with chain cleavage (transacetalization); the reaction of polyoxymethylene cations with methylene groups, however, leads to the transfer of hydride ions (hydride transfer) from the methylene groups to the cations to form methoxy groups. 4 These side reactions have a decisive influence on the molecular weight, molecular and chemical uniformity, and stability of the resulting polyoxymethylenes.…”