Hydrolytic stability of oligoesters: comparison of steric with anchimeric effects

A comparison of steric and anchimeric effects on the hydrolytic stability of polyesters was studied. Twelve monomers were selected based on their propensity toward steric and anchimeric interactions: adipic acid, isophthalic acid, phthalic anhydride, hexahydrophthalic anhydride, 1,4-cyclohexanedicarboxylic acid, maleic anhydride, ethylene glycol, 1,2-propanediol, 1,3-propanediol 1,4-butanediol, 1,5-pentanediol, and neopentyl glycol. Hydroxyl terminated oligoesters consisting of one diacid and one diol and one hydroxyl terminated oligoester consisting of two diacids and one diol were prepared. The hydrolytic stability was evaluated in an acetone/water solution. The acid number was monitored as a function of time. It was found that telechelic groups favor anchimeric interactions, while steric groups determine the rate of hydrolysis for the main chain.