Dynamic Chemistry Of Diselenide Bonds And Its Application In Polymer Materials

Dynamic covalent bonds（DCBs）are covalent bonds that undergo reversible cleavage and formation under certain conditions.Benefitting from their unique dynamic properties,DCBs have been applied in various fields,such as dynamic combinatorial chemistry,stimuli-responsive systems and dynamic materials.Disulfide bonds are one of the DCBs,whose bond energy is around 240 kJ/mol.The bond energy of diselenide bonds are much lower than that of disulfide bonds,which indicates that diselenide bonds can also be DCBs and their dynamic chemistry may require milder condition.With milder stimuli,the dynamic chemistry of diselenide bonds will have better applications in biosystems and materials compared to disulfide bonds.In this thesis,the dynamic chemistry of diselenide bonds have been studied.And then it was applied in the form of diselenide containing dynamic materials.Taking advantage of mild visible light,distinctive processes have been realized with these materials.The work consists of three main topics as follows:1)Diselenide bonds have been studied for their dynamic properties.And for the first time,they were determined to be one of DCBs.The dynamic chemistry of diselenide bonds can be carried out under only mild visible light.Diselenide exchange reaction was characterized by ¹H-NMR and ⁷⁷Se-NMR.The reaction is light dependent,and the mechanism has been confirmed to be radical mechanism.The exchange has been realized also between two diselenide-containing polymers,which confirmed the possibility of using this dynamic chemistry in polymer systems.2)An ebselen moiety containing molecule was synthesized,with which transformation among different selenium containing DCBs has been achieved.After reaction with thiols,the Se-N bond in ebselen moiety was reduced to Se-S bond,then further turned to Se-Se bond.During the transformation,novel Se-S linked macrocycle was produced.When treated with carboxylate anions,the cycle turned to another macrocycle linked by Se-Se bond.In this process,new host-guest chemistry and interactions were involved,which have potential application in supramolecular chemistry.3)Dynamic materials containing diselenide bonds have been fabricated.Diselenide bonds were incorporated into polyurethane（PU）elastomers.With linear PUs,the self-healing properties under visible light were researched.Remotely controlled self-healing was achieved by using a blue laser as the light source.On the other hand,with a cross-linked PU network,visible light-induced plasticity was realized.These materials also possess shape memory properties.Using a commercial projector,designed images could be projected to the materials,thus facile reshaping and patterning were carried out.There are advantages of visible light in polymer materials.The mild visible light can reduce damages to polymer chains during healing and reprocessing.And the diversity of visible light sources provides vast possible applications for these materials.