Synthesis of aliphatic polycarbonates by irreversible polycondensation catalyzed by dilithium tetra-tert-butylzincate

Abstract

Diethyl carbonate was reacted with phenol or 1,6-hexanediol with 5 mol% dilithium tetra-tert-butylzincate (TBZL) as a catalyst at 25 or 70 °C. The exchange reaction with phenol did not occur under these conditions, while that with 1,6-hexanediol did. Thus, polycondensation of diphenyl carbonate with 1,6-hexanediol was investigated. As expected, poly (hexamethylene carbonate) was obtained without removal of the by-product phenol. Conversion reached over 99% with increasing polymerization temperature. Additionally, 1,5-pentandiol and 1,9-nonanediol were also suitable diols for the polycondensation. Aliphatic polycarbonates with number-average molecular weights of 10,000 or more were obtained under optimum polymerization conditions. Polycondensation catalyzed by TBZL proceeded faster than that by titanium tetraisopropoxide, which is used as a general catalyst for polycondensation of diesters, dialkylcarbonates, and diphenyl carbonate with diols. Polycondensations with TBZL proceeded under atmospheric pressure in the presence of the by-product phenol. This polymerization system is expected to be applicable to various diols.