Hydrolysis of some poly(ortho-ester)s in homogeneous solutions

The hydrolysis of poly(ortho-ester)s and a monomeric model compound, 3,9-dibenzyloxy-3,9-diethyl-2,4,8,10-tetraoxaspiro[5,5]un decane, was carried out in dioxane-d8-dioxane and followed by 1H-NMR and HPLC, respectively. Experimental results suggested that the polymer degradation proceeds to a large extent via random scission. The hydrolysis was catalyzed by the acid; the catalytic rate constant increased predictably with decreasing aqueous pKa of the acid. The reaction is first order with respect to the catalyst concentration and the number of ortho-ester linkages present, and it is independent of water in the concentration range studied. Strain at the ortho-ester bond may be a factor influencing the hydrolysis rate.