SYNTHESIS, CHARACTERIZATION AND DEGRADATION OF ALIPHATIC POLYANHYDRIDES

Poly(adipic anhydride) (PAA), poly(sebacic anhydride) (PSA) and poly(dodecanoic anhydride (PDA) were prepared from the mixed anhydrides of diacids and ketene (in tetrahydrofuran (THF) solution), the mixed anhydrides being subjected to melt polycondensation. The polymerizations were carried out in the presence of diethyl zinc as a catalyst. The polymers were characterized by means of 1H NMR, IR spectroscopy, differential scanning calorimetry (DSC) and gel permeation chromatography (GPC). The polymer yields and the molecular weights of the polymers increased in the presence of catalyst. From these results a mechanism for the reaction is proposed. The highest melting temperature of the resultant polymers was obtained from PDA (Tpeak = 90°C). The heat of fusion was approximately 100 J/g (PDA). The number-average and weight-average molecular weights of the polyanhydrides were 18 000 and 33 000 respectively (PDA). Poly(anhydride-b-poly(ethylene glycol) and poly(anhydride)-b-poly(tetramethylene glycol) copolymers were prepared from the mixed anhydrides of dodecanoic acid, poly(ethylene glycol)-succinic half-ester and poly(tetramethylene glycol)-succinic half-ester respectively. The block copolymers were characterized by means of 1H NMR, IR and GPC. The hydrolytic degradation of PDA has been studied in a buffered salt solution (pH 7.2) at 37°C by examining the changes in molecular weight, heat of fusion, mass loss and surface structure of melt-pressed PDA strips.