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.