Synthesis and properties of multifunctional thiol crosslinked gels containing disulfide bond in the network structure

Joint crosslinked gels containing disulfide linkage have been synthesized by oxidation reaction of multi-functional thiol monomers, trimethylolpropane tris(3-mercaptopropionate), tris-[3-mercaptopropionyloxy-ethyl]-isocyanurate, pentaerythritol tetrakis (3-mercaptopropionate), and dipenta-erythritol hexakis (3-mercaptopropionate) in dimethyl sulfoxide (DMSO). Both the oxidation reactions with DMSO at 85 °C and Albright-Goldman oxidation in the presence of acetic anhydride at 50 °C yielded the corresponding gels. The oxidation reaction with DMSO showed higher reaction conversion than that with Albright-Goldman oxidation. Network structure of the gels was quantitatively characterized by means of a scanning microscopic light scattering. The reactions formed homogeneous network structure with about 0.5 nm of mesh in the gels. Mechanical properties of the obtained gels were investigated by compression test. Increasing of the crosslinking density with increasing of the monomer concentration, number of thiol group of the monomer or reaction conversion, raised Young's modulus, and breaking stress of the gels. Cogelation of the tri-, tetra-, of hexa-thiol monomer and dithiol monomers yielded soft and flexible gels. Reduction of the disulfide bonds in the gels by dithiothreitol turned the gel into solution. Heating of the resulting solution induced the regelation by reforming of the disulfide bonds.