Studies On Design Of Dynamic Boronic Ester-Contained Rubbers And Their Strengthening And Toughening Effects Based On Sacrificial Bonds

Diene rubbers are kinds of rubbers polymerized by hydrocarbons containing conjugated double bonds.Because of their excellent physical and mechanical properties,such as high tensile strength and modulus,good wear resistance and aging resistance,diene rubbers have been widely used in industries and daily life.For practical applications,the cross-linking of rubbers is essential.Traditional crosslinking methods using peroxides or sulfur curing packages yield irreversible covalent cross-links in the network,which prevents their being healed or reprocessed,resulting in resource waste and environmental pollution.In order to prolong their service lifetime and make diene rubbers recyclable,dynamic covalent bonds have been introduced into rubbers.The reversibility of dynamic covalent bonds allows the rearrangement of cross-linked network,thus endowing the materials healability and reprocessability.In addition,the reinforcement of rubber and expanding their application areas are also two important issues.Therefore,it is of great significance to prepare diene rubbers with healability,reprocessability and excellent mechanical properties.In this study,diene rubbers and their derivatives are cross-linked by the boronic ester-crosslinker.Based on the dynamic exchange reactions of boronic ester bonds,the cross-linked network can rearrange and relax stress upon heating,thus imparting the cross-linked network with healability and reprocessability.Furthermore,sacrificial bonds are introduced into the cross-linked network,which can enhance the mechanical properties of diene rubbers and endow the shape memory function.The thesis includes four parts as described below.2,2'-(1,4-Phenylene)-bis[4-mercaptan-1,3,2-dioxaborolane](BDB)containing boronic ester bonds and di-thiols is synthesized.Based on the facile yet efficient "thiol-ene" click reactions,SBR is cross-linked by BDB,by which dynamic boronic ester bonds are introduced into the network.The boronic ester-crosslinked SBR exhibit relatively good mechanical properties,excellent healability and reprocessability.Based on open-ring reactions between thiol groups of BDB and epoxy groups of epoxidized natural rubber(ENR),boroinc ester bonds are introduced into the ENR by simple blending BDB and ENR in open-mill,followed by hot-pressing.Cross-linked ENR with excellent mechanical properties(tensile strength up to 14 MPa,elongation at break up to 475 %),high healing efficiency(healing efficiency over 90 %,24 h @ 80 °C)and reprocessability(mechanical properties recovery ratio over 70 %)is prepared.Hydrogen bonds are introduced into boronic ester-crosslinked SBR based on the 4-phenyl-3H-1,2,4-triazoline-3,5-dione(TAD)click reactions.Hydrogen bonds act as sacrificial bonds and dissipate energy through reversible dissociation/reconstruction of the hydrogen bonds,significantly enhancing the tensile strength and modulus of SBR.Because of the responsiveness of hydrogen bond clusters to temperature and the dynamic nature of boronic ester bonds,the rubber exhibits shape memory and reconfiguration effects.Zinc chloride is introduced into the boronic ester-crosslinked ENR to construct Zn(II)-O coordination bonds in the network.The Zn(II)-O coordination bonds are sacrificial and can strengthen and toughen ENR significantly.The Zn(II)-O coordination bonds dissociate at high temperatures and thus have little detrimental effect on the exchange reactions of boronic ester bonds,which maintains the healability and reprocessability of the cross-linked ENR.