Thiol-Dibromomaleimide Polymerization: A Simple Strategy for Easily Degradable and Modifiable Polythioether Synthesis

In this study, linear poly(maleimide thioether)s were prepared by thiol-dibromomaleimide (thiol-DBM) reaction using 2,3-dibromomaleimide (DBM) and dithiol monomers. Various parameters, such as solvent, reactant concentration, and time, were initially screened to reveal the optimum conditions for polymerization. A wide range of dithiols were then reacted with DBM under optimum conditions. The polymerizations proceed in a substitution mechanism, resulting in an unsaturated maleimide backbone along the main chain, accompanied by pendant imide N-H groups. Polymers were obtained in high yields with varying molecular weights ranging from 7.3 to 68.2 kDa. Postpolymerization modification of the pendant N-H groups was achieved via imide-yne click reaction with various propiolates using an organocatalyst 1,4-diazabicyclo[2.2.2]octane (DABCO). All synthesized polymers displayed a wide range of glass transition temperatures depending on the type of dithiols used. The obtained poly(maleimide thioether)s were found to be readily degradable in the presence of a monothiol; a degradation study was performed on a model polymer and a cross-linked structure using an excess amount of 1-propanethiol in the presence of triethylamine (TEA). We believe the presented chemistry is practical, offering a time- and energy-saving approach, and may pave the way for new developments in polymer synthesis, functionalization, and degradation.