The Soap Opera of Metal Catalysis in Epoxy-Acid Vitrimers

Precipitation of bivalent metal carboxylates is a well-known issue in detergency, resulting in decreased efficiency and unwanted accumulation of lime soap on laundry. We demonstrate that the same phenomenon occurs in formulations of metal-catalyzed epoxy-acid vitrimers. When, for instance, a Zn(II) salt and glutaric acid are allowed to be in contact with each other in the same reaction feedstock, precipitation takes place, resulting in phase separation of zinc glutarate and a glutarate-poor polymer network, showing no vitrimer properties. We present a strategy to overcome this issue based on step addition at a single end of the dicarboxylic acid monomer prior to contacting with zinc. In this case, formation of crystalline zinc soap is completely avoided, and the network shows thermostimulated stress relaxation. This strategy is particularly appealing for the synthesis of polyhydroxyester networks showing high-glass-transition temperature and fast relaxation.