Investigation of the structure, filler interaction and degradation of disulfide elastomers made by Reversible Radical Recombination Polymerization (R3P)

In this paper we report the synthesis and analysis of cyclic polydisulfides, their redox depolymerization as well as their interaction with carbon black. Cyclic poly(3,6-dioxa-1,8-octanedithiol)s (pDODT) were synthesized by Reversible Radical Recombination Polymerization (R3P). R3P is a scalable green polymerization process using triethylamine (TEA), H2O2 and air for the polymerization of dithiol monomers. pDODTs were synthesized in 5 and 20 g batches. The effect of peroxide concentration (3, 5, 10, 20, 30 %) was investigated. It was found that the molecular weights increased exponentially with increasing peroxide concentrations. At 30 % peroxide concen-tration pDODTs with Mn up to 400,000 g/mol and polydispersity of 2 were obtained. 700 and 800 MHz NMR were used for investigating the chemical structure of the polymers. The absence of thiol end group signals in polymers made with > 10 wt % H2O2 and Mn < 100,000 g/mol, including a sample of a fractionated polymer with starting Mn = 600,000 g/mol, verified cyclic structures. Dithiothreitol reduced the polymers to monomer and a small percentage of oligomers. Carbon black was shown to increase the moduli of high molecular weight pDODTs. Swelling tests in chloroform showed that polymers made with 20 and 30 w% peroxide swelled 14 and 10 times of their starting weight without dissolving, indicating chemical interaction between the polymers and carbon black. Further analysis of these interesting elastomers, available at the 20 g scale, is in progress.

Automated summary

In this paper, the synthesis and analysis of cyclic polydisulfides, their redox depolymerization, and their interaction with carbon black were reported. Cyclic poly(3,6-dioxa-1,8-octanedithiol)s (pDODT) were synthesized using Reversible Radical Recombination Polymerization (R3P) with varying peroxide concentrations. The molecular weights of pDODTs increased exponentially with increasing peroxide concentrations. NMR analysis confirmed the presence of cyclic structures in pDODTs made with >10 wt % H2O2 and Mn <100,000 g/mol. Dithiothreitol reduced the polymers to monomers and oligomers, and carbon black showed chemical interaction with the polymers. Further analysis of these elastomers is underway.