Synthesis and depolymerization of self-immolative poly(disulfide)s with saturated aliphatic backbones

Self-immolative polymers (SIPs) are a class of degradable stimuli-responsive polymers, which, upon removal of labile end-caps, depolymerize selectively and stepwise to small molecules. In light of our recent discovery of poly(dithiothreitol) (pDTT), a versatile SIP with a remarkably simple synthesis procedure, we investigated a broader range of unfunctionalized poly(disulfide)s. It is demonstrated that saturated aliphatic backbones can easily be made from 1,4-butanedithiol, 1,5-pentanedithiol, and 1,6-hexanedithiol monomers and, compared with pDTT, these polymers show enhanced stability, solubility, and processability. SIP polymers derived from the smaller 1,3-propanedithiol monomer with end-caps installed could not be synthesized. Polymers of 1,4-butanedithiol and 1,5-pentanedithiol undergo end-to-end depolymerizations upon end-cap removal, taking hours to days under basic conditions and not minutes as for pDTT. Degradation of the polymer of 1,6-hexanedithiol occurs by less well-defined pathways providing a complex product mixture of macrocyclic disulfides.