Effect of monomer composition on thermal, mechanical, and self-healing properties of thermosets containing Diels-Alder adduct moieties and disulfide bonds

The Diels-Alder (DA) and thiol-maleimide reactions of difurfuryl disulfide (DFDS), 1,4-bismaleimidodiphenylmethane (BMI), pentaerythritol tetrakis(3-mercaptopropionate) (PETMP), and thiol-terminated disulfide-containing polyether (LP) at various feed monomer ratios produced polymer networks containing both DA adduct moieties and disulfide bonds. Fourier transform infrared spectral analysis revealed that the DA and thiol-maleimide reactions occurred for all the cured products. A differential thermal analysis revealed that all the cured products exhibited an endothermal peak due to the retro-DA reaction at 115–124 °C. The tensile moduli and strengths of the cured products increased with increasing DFDS (or DA) and PETMP fractions. The elongations at break increased with increasing LP (or disulfide) fraction. Most of the cured products exhibited self-healing ability by annealing at 60 °C for 24 h, and/or at 120 °C for 1 h followed by additional annealing at 60 °C for 24 h. The cured product with a higher LP (or disulfide) fraction exhibited a better healing ability at 60 °C for 24 h by the disulfide metathesis. Also, the cured product with a higher DFDS fraction exhibited a better healing ability at 120 °C for 1 h and 60 °C for 24 h by the DA/retro-DA reaction.