Facile design of degradable poly(β-thioester)s with tunable structure and functionality

The synthesis of a range of linear biodegradable poly(β-thioester)s, PBTs, via hexylamine-catalyzed thiol-ene Micheal additions between a variety of diacrylate and dithiol monomers is described. Molecular weights up to 12,000 g mol^-1 are obtained for this new class of polymer materials. PBTs featuring very different chemical and mechanical behavior are obtained on the basis of seven diacrylate and three dithiol monomers. Polar PBTs are synthesized based on ethylene glycol-containing monomers in an environmentally friendly solvent. Furthermore, PBTs containing urethane units in the main chain are obtained, providing access to an isocyanate-free polyurethane polymerization method. The thiol-ene addition approach can also be used to couple polystyrene oligomers synthesized from a bifunctional trithiocarbonate reversible addition fragmentation transfer agent. In this way, PBTs featuring polystyrene segments as well as diacrylate segments are produced. In general for these step-growth polymerizations, by tuning the stoichiometric monomer ratio, a desired end group functionality can be quantitatively introduced into the PBT, which is demonstrated via soft ionization mass spectrometry analysis. As an example, alkyne end groups have been built in, giving access to use these materials in modular polymer design strategies.