Ring-Opening Polymerization of Propylene Oxide by Double Metal Complex in Micro-Reactor

The ring-opening polymerization of propylene oxide catalyzed by double metal complex (DMC) is carried out in continuous micro-reactor (C-MR). It is found that the monomer conversion at the C-MR outlet is usually 100% within 2 min of average residence time, which means that the polymerization rate in the C-MR is faster than that in a traditional semi-continuous tank reactor. However, the induction period still exists in the polymerization in C-MR, but can be shortened by increasing the reaction temperature or the micro-reactor length. The mechanism of monomer coordination and ring opening on DMC during the induction period is confirmed by the H-1 NMR analysis of the samples obtained under very short average residence time. The molecular weight distribution (MWD) of product from C-MR is generally narrow, which indicates that the process still maintain the characteristics of the "living" polymerization. That is, there is a very high rate ratio of chain transfer to chain propagation provided by the DMC catalyst. However, with the same average residence time, the MWD of product from the longer C-MR is broader, which can be attributed to the increase of the chain propagation rate caused by rise of pressure.