Bicyclic acetal polymerization reactivity

In general, bicyclic acetals are highly reactive toward acid-catalyzed hydrolysis. For example, the hydrolysis of 2,7-dioxabicyclo[2.2.1]heptane (2) in aqueous acetone containing dichloroacetic acid was 2.5 x 104 times faster than that of an acyclic reference compound, dimethyl acetal. [77] 2,6-Dioxabicyclo[Z2.1]heptane (79) is more reactive, and hydrolyzed 6.9 x 10s times faster than dimethyl acetal. [78] These rate accelerations for bicyclic acetals arise from a partial liberation of the ring strain on hydrolysis, and have been correlated to the reactivities of bicyclic acetals in the cationic ring-opening polymerization. [5]... 

Reactivity. The reactivities of the bicyclic orthoesters can be compared examining the conditions necessary to form polymer. Although the hydrolytic reactivities were not accelerated, these monomers were Indeed very reactive In polymerization. In contrast to the behavior of the bicyclic acetals, no correlation Is found between the hydrolytic reactivity and the reactivity towards cationic Initiators for the bicyclic orthoesters. The following order can be proposed [2.2.1] > [2.2.2] > [3.2.1] > [3.3.1] which Is the expected order from the ring strains (18-19). 

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