Synthesis and stabilization of high-molecular-weight poly(propylene carbonate) from Zn-Co-based double metal cyanide catalyst

High-molecular-weight poly(propylene carbonate) (PPC) was synthesized using a Zn-Co-based double metal cyanide (Co-DMC) catalyst. The catalytic activity reached as high as 60.6 kg polymer/g Co-DMC after 10 h when the low-molecular-weight polyether polyol initiator was not used. In contrast, production of the by-product propylene carbonate (PC) significantly decreased to below 1.0 wt%. Considering the carbonate content in the alternative copolymer as 100%, the carbonate content of the obtained PPC ranged between 34% and 49%. The carbonate content was highly important for the air stability of PPC. The number average molecular weight of the as-polymerized PPC with a carbonate content of 48% reached 130 kg/mol. However, it decreased to ca. 60 kg/mol after 24 h of storage at 70 C, and further dropped to ca. 40 kg/mol after 7 d. This result confirmed that severe oxidative degradation occurred for the low-carbonate-content PPC. Air stability significantly improved by adding antioxidant 1010 (tetrakisl methylene(3,5-di-(tert-butyl)-4-hydroxy-hydro cinnamate)] methane). Similarly, a more air stable PPC was also prepared by raising its carbonate content. Our work provided a new explanation on the wide existence of low-molecular-weight PPC in DMC catalyst literature. Strategies for obtaining high-molecular-weight PPC were also disclosed. (C) 2011 Elsevier Ltd. All rights reserved.