Investigation On Preparation And Performance Of Cis-polyisoprene With Dual-Crosslink

Although synthetic cis-1,4-polyisoprene?IR?possesses almost the same molecular structure to NR,IR exhibits much lower mechanical properties than its natural counterpart.It has been widely acknowledged that the non-rubber components in NR can promote the strain-induced crystallization?SIC?,which is closely related to the excellent mechanical properties of NR.Therefore,simulating the effect of non-rubber components and constructing multinetwork via modification of IR to gain superior mechanical properties are of great importance,which can not only provide a new way to reinforce rubber but also solve the problem of the shortage of NR.Traditionally,most researches have focused on the introduction of nanofillers into IR to enhance mechanical performance.Although in most cases,the incorporation of various nanofillers is sufficient to obtain satisfied mechanical properties,there are still some important limitations or difficulties for nanofilling,such as dispersion/interface regulation and processing difficulties.By contrast,the method of using sacrificial bonds to reinforce rubber can not only improve the mechanical properties of rubber but also avoid the limitations from the nanofilling.Sacrificial bonds exist in many natural materials such as spider silk and mussel byssus.During stretching,sacrificial bonds can be destroyed prior to covalent bonds and dissipate plenty of energy,which is beneficial to the improvement in mechanical properties of rubbers.In recent years,there is increasing interest on reinforcing common rubbers with sacrificial bonds strategy.However,those reports about sacrificial bonds are mainly focused on hydrogen bonding or metal-ligand coordination,and ionic interactions with high binding energy serving as sacrificial bonds has been rarely reported.Based on the above background,this research is aim at introducing ionic bonds into sulfide-cured IR by chemical modification to prepare dual-crosslinked IR.The mechanical performance of modified IR and its blends have been studied in detail.The main contents of this dissertation are as follows.?1?The sulfonic acid groups were grafted onto IR to obtain the modified IR?IR-SO₃H?.The amino-functionalized carbon nanodots?CDs?were prepared using ethene diamine as the passivating agent.Dispersed CDs behave as high functionality cross-linkers?HFC?due to the formation of ionic bonds between the sulfonic acid groups and amino groups.Simultaneously,the sulfide-based crosslinking was introduced to create the IR network with dual-crosslink.The introduction of ionic bonds led to higher crosslinking density.The preferential fracture of ionic crosslinks promoted the chain orientation process and hence promoted the the SIC of IR.Consequently,the mechanical performance was increased.?2?Aiming to reveal effects of the subtle structural changes of ionic bonds on the mechanical properties of IR,diamine and sulfur curing package were simultaneously introduced into a sulfonated IR?IR-SO₃H?to create IR network with dual-crosslink.The ionic bonds formed between sulfonic acid and diamine act as sacrificial bonds.Three kinds of diamine with the same carbon chain but different alkalinity are used to create the ionic bonds with different binding energies.The research shows that the capabilities of diamine in dissipating energy,promoting stain-induced crystallization and enhancing the mechanical performance are in the same order.The stronger alkalinity of amine is,the higher binding energy of ionic bonds and the more excellent mechanical performance are.?3?To explore the application of IR with dual-crosslink,small fraction of IR-SO₃H,acting as the dispersed phase,was blended into butadiene-styrene-vinyl pyridine rubber?VPR?.The sulfur curing package were introduced into the mixture to cure the rubber blend.The result showed that a part of IR-SO₃H could wrapped around the zinc oxide particles by the fomation of zinc sulfonate.Another part of IR-SO₃H would disperse in VPR randomly due to the phase separation.In addition,strong interfacical interaction between IR and VPR resulted due to the formation of ionic bonding between the sulfonic acid groups and pyridine groups.The ionic bonds could be fractured preferentially during stretching,resulting in energy dissipation and improvement in mechanical properties of VPR.The tensile modulus?stress at strain of 100%?of the blend with 20 phr of IR-SO₃H was improved more than three times,comparing to the neat VPR.