Degradable Acrylate-Telechelic Copolymers with Disulfide and β-Thioester Linkages by Simultaneous Thiol Oxidation and Thiol-Ene Michael Addition Click Reactions with the Same Base Catalyst.

This study reports on a new one-pot copolymerization process by simultaneous oxidative disulfide and β-thioester formation by reacting bifunctional monomers, 3,6-dioxa-1,8-octane-dithiol (DODT) with diacrylates, poly(ethylene glycol) diacrylate (PEGDA) and 1,6-hexanediol diacrylate (HDODA), in the presence of N,N,N',N″,N″-pentamethyldiethylenetriamine (PMDETA), as the same base catalyst for both reactions, in air at room temperature with short reaction times. The resulting random copolymers consist of disulfide linkages between DODTs and β-thioester units formed by thiol-ene Michael addition click reaction. With a stoichiometric DODT/diacrylate feed ratio, diacrylate-telechelic copolymers are obtained in a single-step polymerization reaction. The Tgs of the P(DODT-co-PEGDA) copolymers are nearly constant at around -53 °C, while it decreases with increasing HDODA content in the P(DODT-co-HDODA) copolymers. Reductive degradation with thiols, such as 2-mercaptoethanol and dithiothreitol, led to chain scission via the disulfide-thiol exchange reaction. Treatment with NaOH solution resulted in further degradation by hydrolysis of the β-thioester units. These results indicate that these novel copolymers are fully degradable under mild conditions. This new process, applying simultaneous thiol oxidation and thiol-ene reactions, enables to prepare a large variety of sulfur-containing end-functional degradable copolymers useful for a broad range of advanced application possibilities.