Green Polymer Chemistry: Living Dithiol Polymerization via Cyclic Intermediates

This paper reports the synthesis and characterization of disulfide polymers obtained by oxidation of 2-[2-(2-sulfanylethoxy)ethoxy]ethanethiol (DODT) using a benign, synergistic system comprised of air, dilute hydrogen peroxide and triethylamine as a catalyst that can be recycled. The dn/dc value of the polymer in THF was determined to obtain absolute molecular weight measurements. High molecular weight disulfide polymers (up to M-n = 250000 g/mol) with polydispersity indices as low as M-w/M-n = 1.15 were obtained. Thermal analysis by DSC and TGA demonstrated that the rubbery polymers had a T-g of -50 degrees C and began to degrade at 250 degrees C. Dithiothreitol reduced the polymers back to the original monomeric units in 33 h. MALDI-ToF showed the involvement of oligodisulfide rings (2-14 mers) in the polymerization that displayed the characteristics of a living/controlled polymerization; poly(DODT) was readily chain extended with 1,2-ethanedithiol. The chain extension indicates a class of living polymerization which is governed by radical recombination.