Selective single ring‐opening polymerization of spiroorthoesters with aluminium (III) acetylacetonate

A spiroorthoester, 2‐methyl‐1,4,6‐trioxaspiro[4.6]undecane ( 1 ), was polymerized with aluminium (III) acetylacetonate as a catalyst. The resulting polymer structure was analyzed in detail by FT‐IR and 270 MHz 1 H NMR, and consisted of poly(orthoester) which was obtained by selective ring‐opening of the seven‐membered ring. In contrast, 2‐methyl‐1,4,6‐trioxaspiro[4.5]decane ( 2 ) and 2‐methyl‐1,4,6‐trioxaspiro[4.4]nonane ( 3 ) did not afford any polymers. The reactivity difference of these monomers was discussed in terms of their strain energies on the basis of MM2 calculations.