Controlled Oxidation of a Tetrafunctional Thiol to Obtain a Poly (Thiol- disulfide) Oligomer and Its Use as Self-healing Agent for Epoxy/Thiol-ene Photocurable Systems

In this work the pentaerythritol tetrakis (3-mercaptopropionate) was partially oxidized to obtain an
oligomer with both thiol and disulfide functional groups in its structure, by using iodobenzene diacetate
(IBDA) as oxidant. This oligomer was used to introduce disulfide bonds into the crosslinked network of
a polyether-polythioether matrix obtained by photopolymerizing an epoxy/thiol-ene system. The
presence of the disulfide bonds induced self-healing properties bonds in the obtained co-network. The
oligomer was a joint component of the thiol-ene system along with a tetraallyl-functionalized ditertiary
amine curing agent and a radical photoinitiator. The thiol groups of the oligomer reacted with the
double bonds of the curing agent to form polythioethers, while the tertiary amine groups of the curing
agent induced the anionic ring opening polymerization of the oxirane groups of an epoxy resin to
produce polyethers. The kinetics of photopolymerization of the epoxy resin diglycidylether of
bisphenol A (DGEBA), revealed that conversions of the epoxy groups as high as 80 % were achieved
in only fifteen minutes by increasing the concentration of the thiol-ene system in the formulation. The
disulfide bonds introduced in the co-network by using the thiol-disulfide oligomer, allowed the
repairing of the test specimens in as little as 10 minutes when the specimens were heated at 80 °C or
for 500 minutes at room temperature. The analysis of mechanical properties using dynamic
mechanical analysis (DMA) showed that the healed specimens, retained their mechanical properties
depending on the amount of polythioethers present in the co-network.