Reinforcement Of Rubbers Via Multi-Functionality Crosslinking And Sacrificial Bonding Strategy

The reinforcement of rubbers for practical applications is essential as most neat rubbers exhibit poor mechanical properties.The most common method for rubber reinforcing is the incorporation of various nanofillers.However,this method depends heavily on the dispersion of nanofillers and the interface interactions between rubbers and fillers.Besides,high amount of fillers is required for desired mechanical properties,which makes a negative effect on the specific strength of rubbers.To solve this predicament,the author proposed the reinforcing methods based the multi-functionality crosslinking and sacrificial bonding strategy.?1?The rubber with high modulus is prepared by the crosslinking strategy with high-functionality crosslinker via oxa-Michael reaction.The solution-polymerized styrene-butadiene rubber?SSBR?is firstly hydroxylated by thiol-ene click reaction.It is revealed that the modified SSBR can be effectively cured by various acrylates via oxa-Michael reaction.By improving functionality of acrylates,the tensile strength and modulus can be improved obviously.The mechanical properties of vulcanizates also increase with the increases in crosslinker content and hydroxyl content.The correlation between mechanical properties and network structure is accordingly achieved,which provides essential base for the future application of the diene rubbers cured by oxa-Michael reaction.?2?Inspired by the structures of the mussel byssus,ferric ions are introduced into an oxygen-abundant epoxidized natural rubber?ENR?network to create additional metal-oxygen coordination cross-links.Such complexations are revealed to be highly efficient in enhancing the modulus,strength and toughness of the rubbers.The main mechanism for the improved mechanical properties is due to sacrificial nature of coordination,which can preferentially break during stretching,prior to the rupture of the sulfide-based crosslinks.The dynamic rupture and re-attaching of the metal-oxygen bonds lead to efficient dissipation of mechanical energy and the suppression of stress concentration.In addition,the continuous shifting of glass transition enables the design of highly damping material with a multilayer concept.Such physical cross-links also serve as additional mechanism for fixing the temporary shape,resulting in an excellent and tunable multiple memory effect.We envision that the present work offers an efficient yet facile way of creating advanced elastomers based on industrially available diene-based rubber.?3?A very strong elastomer is successfully developed by introducing Fe^III-OH coordination into a covalently crosslinked SSBR.Such hydroxy-based coordination can efficiently improve the mechanical properties of the elastomer.With introduction of 4.2 wt%Fe³⁺,the elastomer exhibits a tensile strength of 20.9 MPa and a modulus of 12.7 MPa,which is 7 and 9 times of those for neat SSBR.The achieved mechanical properties are competitive to the highly-filled engineering rubbers.The drastically improved mechanical properties should be ascribed to the quite high binding energy of Fe^III-OH coordination,which works in a sacrificial manner by dissipating energy and suppressing stress concentration.As hydroxylated polymers can be prepared readily with commercially available polymers,the present study should promote comprehensive research and industrial applications of sacrificial bond strategy.?4?It is revealed that the polysulfide crosslinks can coordinate with metal ions in the sulfur-crosslinked rubber,leading to significantly reinforced rubber.It is demonstrated that two metal ions,Cu²⁺and Fe³⁺,exhibit a synergistic effect on the rubber reinforcement.Compared with rubber containing single metal ion,the rubber with two metal ions exhibits drastically improved mechanical properties.This phenomenon is mainly ascribed to the difference in the binding energy of polysulfide-Cu²⁺and polysulfide-Fe³⁺,which can break successively in a sacrificial manner.Besides,increasing sulfur content and metal ions concentration can further improve the mechanical properties of the rubber.Significantly,the coordination is constructed with the crosslink-based moieties in sulfur-crosslinked rubber as ligand,leading to a strong dual-crosslinked rubber without any chemical modification.?5?A facile yet efficient multiphase method for reinforcing nonpolar rubbers via sacrificial strategy is proposed.The created dispersed microphases in the nonpolar matrix is the ferric ion coordinated ENR.The microphase can serve as an additional cross-link to improve the modulus,while it is deformable when subjected to an external force via the rupture-reconstruction of coordination.Consequently,elastomers with such biomimetic structures exhibit a combination of high modulus,high stretchability and recoverability.The Young's modulus,tensile strength,and toughness are 2.8,7.0 and 11.4 times higher than those for the control sample.Importantly,this strategy utilizes easily available raw materials and does not rely on special processing.In addition,this method is generic and can be applicable to various non-polar rubbers.