The Study On The Modification Of Elastomer Via Thiol-ene Click Reaction

This study is focused on the modification of poly(styrene-b-butadiene-b-styrene)(SBS)via the thiol-ene click reaction to graft the function groups to the PB block.Functional groups are induced into the polymer system to achieve different smart behaviors including self-healing and shape memory behavior with improving the solvent resistance and mechanical properties for SBS.The detailed studies are shown as follow:(1)SBS/POSS hybrids: POSS with thiol groups was applied as crosslinkers to build crosslinked SBS hybrids via the thiol-ene click reaction.In this way,POSS was dispersed in the matrix at a molecular level.The formation of this inorganic-organic crosslinked structure can effectively improve mechanical properties of SBS,including the storage modulus and strength without residual elongation in the cyclic tensile tests at very small loading.Only addition of a very small amount(0.3 wt%)of POSS-SH can increase the stress at break of composites from 1.9 to 16.2 MPa,almost 8.5 times higher.The maximum of stress at break was observed at 23.4 MPa for the sample with 1 wt% POSS-SH.In the meantime,the elongation at break was still kept at about 1000%,which is not usually observed in the conventional inorganic filler reinforced elastomer.(2)SBS/BZ composite: The thiol functionalized benzoxazine(PTMP-BZ)was attached to the chains of SBS via the thiol-ene click reaction to form the first crosslinked network and the second crosslinked structure was further formed in SBS matrix via the ring opening of the attached benzoxazine.In this way,the compatibility between thermosetting resin(BZ)and SBS was improved with noticeable solvent resistance and resilience of SBS as well as its tensile strength and storage modulus.The final tensile strength at break showed an almost 9-fold increase on that of pure SBS after two reactions.At the same time,the elongation at break was still kept at about 1000%.(3)Dynamically crosslinked SBS: SBS was grafted with furan groups(SBS-Fu)via the thiol-ene click reaction and then reacted with bismaleimide to form thermally dynamic crosslinking linkage via the Diels-Alder reaction.The crosslinking degree and mechanical properties of crosslinked SBS can be tuned by adjusting the ratio of furan group to the double bonds on PB block and the ratio bismaleimide to furan.For SBS–5Fu–M,the tensile strength and tensile strain at break were 14.47 MPa,706.4% respectively,the tensile strength almost increased by 8 times as compared with the pure SBS.Compared with previous works,this kind of dynamically crosslinked SBS can be still thermal-plastically remolded due to the de-crosslinking reaction via rDA reaction at the higher temperature,and the mechanical properties,solvent resistance and resilience were also improved at the same time.(4)SBS/C60 hybrids: C60 acting as dienophile was used to crosslink SBS-Fu via the Diels-Alder(DA)reaction.In this way,C60 was dispersed in the matrix in molecular level without aggregation.with the presence of 0.1 wt% C60,the tensile strength and strain at break for SBS-20Fu-0.1C60 were observed at 14.82 MPa and 977.34% respectively,almost 8.5 times increase in tensile strength as compared with the pure SBS.However,without the presence of DA reaction,SBS-0.1C60 only showed the tensile strength and strain at break at 2.83 MPa,1270.8% respectively,only 1.64 times increase in tensile strength as compared with the pure SBS.The solvent existence,elastic resilience and tensile strength of the hybrids were greatly improved with the incorporation of C60,and the hybrids possessed the self-healing and remolding abilities via retro-Diels-Alder(rDA)reaction.(5)SBS/CNTs hybrids: The pristine carbon nanotubes were acted as dienophile to crosslink the SBS-Fu to fabricate the SBS/CNTs hybrids via a Diels-Alder reaction.The mechanical properties as well as resilience and solvent resistance were greatly improved even with the presence of only 1 wt% CNTs.Meanwhile,the hybrids retained recyclability and exhibited good self-healing and reprogrammable shape memory properties.Combining with the photo-thermal effect of CNTs,the rDA reaction in the hybrids can be controlled with laser in the remoted way.This hybrid exhibited laser remoting smart behaviors including self-healing and reprogrammed shape memory properties.Furthermore,the DA and rDA reactions could be combined to reprogram the shape memory behavior under laser irradiation or thermal treatment,wherein the temporary shape of the sample could be transferred to a permanent shape via the rDA reaction at high temperature.