SYNTHESIS AND CHARACTERIZATION OF SELF-CATALYZED POLY(ORTHO ESTER)

Poly(ortho eaters) are currently under investigation as a carrier syst em for an antiproliferative agent in glaucoma filtering surgery. The p resent investigation illustrates the development of a series of self-c atalyzed poly(ortho ester). These polymers contain short dimer segment s of alpha-hydroxy acids in their backbone and are prepared by the add ition of different polyols to the diketene acetal ethylidene-2,4,8,10- tetra-oxaspiro-[5.5]-undecane. The structures were confirmed by NMR- a nd FT-IR-spectroscopy. The polymers were characterized by determinatio n of the molecular weight, the glass transition temperature and the rh eological behavior. The amount of residual solvents was also analyzed. The characteristics of the polymer can be varied by the type of polyo l incorporated in its backbone. Since poly(ortho ester) is susceptible to acid-catalyzed degradation, the polymer hydrolysis can be controll ed by the amount of incorporated portion of alpha-hydroxy acid. Due to the high hydrophobicity of the polymer structure, the ester bonds are more susceptible to hydrolysis than the ortho eater bonds in the poly mer backbone. The hydrolysis proceeds via initial protonation of the e xocyclic alkoxy group to yield pentaerythritol dipropionate and the fr ee diol. In a next step, the pentaerythritol dipropionate hydrolysis t o pentaerythritol and propionic acid. The molecular weight decrease, w eight loss and the pH profile of the polymer in aqueous medium were mo nitored during the degradation. (C) 1998 Elsevier Science Ltd. All rig hts reserved.