An Environmentally Benign Solvent for the Cationic Polymerization of Low Ceiling Temperature Polyaldehydes

The synthesis of phthalaldehyde-based polymers has exclusively been carried out in dichloromethane, which causes environmental problems due to its halogen content and ozone-depleting attributes. In this study, an alternative solvent for the polymerization of o-phthalaldehyde-based polyaldehydes is disclosed. Ethyl acetate, a solvent that is widely used in consumer products, dissolves a sufficient amount of reactants and polymer product at the reaction conditions, -86 °C, to provide a comparable yield to synthesis in dichloromethane. A significant learning from this study is that the reaction solvent does not have to fully dissolve all the reactants and products to produce stable polymer, compared to dichloromethane, which fully dissolves reactants and products. The polymer product precipitated from the ethyl acetate solution as the polymer formed. Although the reactants and products were not fully soluble in ethyl acetate, they retained sufficient mobility to allow the catalyst to initiate polymer chains and achieve molecular weights as high as 83.4 kg/mol. The synthesis of cyclic copolymers from o-phthalaldehyde and aliphatic aldehydes is also possible in ethyl acetate if the catalyst is added at a temperature below the ceiling temperature of the monomers and above the point where they crystallize from solution.