Transesterification catalyst for aliphatic oligocarbonates

Abstract

Poly(ethylene glycol) is one of the most used stealth polymer in the field of polymer-based drug delivery. In spite of its excellent biocompatibility, high molecular poly(ethylene glycol) can be accumulated in the body, in contrast to low molar mass one. This is due to the non-degradability of poly(ethylene glycol) which can cause some negative side effects. In order to overcome this drawback, in this work we present new degradable high molecular poly(ethylene glycol) by simply incorporating carbonate groups between poly(ethylene glycol) units. Thus, poly(ethylene glycol) based polycarbonates have been synthesized by polycondensation of dimethyl carbonate and poly(ethylene glycol) of four different low molar masses; 600, 1000, 1500 and 2000 g mol−1. Optimum bulk polycondensation reactions were run in two steps in the presence of 4-dimethylaminopyridine organocatalyst. By this method, poly(ethylene glycol) based polycarbonates were prepared and characterized showing molar masses between 10 and 35 kg mol−1 and crystallinity was increased compared to the initial low molar mass poly(ethylene glycol)s. The hydrolytic degradation of the poly(ethylene glycol) based polycarbonates was investigated in vitro using a phosphate buffer solution at pH = 7.2. The results showed that the initial poly(ethylene glycol)-polycarbonates hydrolyzed by the carbonate units showing a decrease of molar mass as a function of time. It was found that all polycarbonates underwent almost complete hydrolysis after 50 days leading to the initial low molar mass poly(ethylene glycol) units that are bellow renal clearance threshold.