Synthesis and Polymerization of Fused Bicyclic Orthoesters

The polymerization of a bicyclic monomer, in which only one or both rings are opened has recently been reported by Hall47. This monomer 2,6,7-trioxabicyclo 2.2.11-heptane (TBH) may be prepared in 73 % yield by the reaction of glycerol and triethyl-orthoformate  

The intensity of the signals due to the orthoformate protons indicates that the polymer contains almost exclusively (90-100%) five-membered rings  

The polymerization is accompanied by approximately 6% shrinkage (calculated from densities of monomer and polymer at 25 °C). Upon heating the polymer solution in the presence of trifluoromethanesulfonic acid the substituted 1,3-dioxolane ring opens and linear polymer is formed. This is accompanied by a 9.7% expansion in volume. 

Bulk polymerization of 2,6,7-trioxabicyclo 2.2.1 heptane with 1 mol% CF3S03H initiator at 80 °C directly gives linear polymer with a quantiative yield (after 1 h). The structure of this polymer was determined from H-NMR spectra, which showed 

Comparison of the intensities of the corresponding signals indicated that the linear polymer contains two types of units  

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