The Synthesis Of PRCo And Study Of The CD Motion Performance

Polyrotaxanes（PRs）have being aroused tremendous interesting due to their novel mechanically interlocked supramolecular structure and great potential to be used as smart materials since Harada et al.Firstly reported the preparation of polypseudorotaxanes（PPRs）self-assembled from a varying amount ofα-cyclodextrins（α-CDs）with PEG followed by end-capping using bulky stoppers.The sliding and rotating motion ability of those threadedα-CDs along the polymeric axis endows the resulting PRs with the unique dynamic and stimulus response performance.Alternatively,the PR-based copolymers（PRCos）can be fabricated from PPRs using the in situ atom transfer radical polymerization（ATRP）of hydrophilic vinyl monomers as an end-capping technique via“one step”strategy.However,this strategy was often challenged with a severe de-threading problem of CDs off the polymeric axis when it was employed to conduct ATRP of hydrophobic vinyl monomers as end-capping stoppers of PPRs.To solve the problem,a“two step”strategy was proposed to utilize PR-based initiators instead of PPR-based ones to initiate ATRP of hydrophobic vinyl monomers to prepare PRCos.Firstly,the PR-based initiators were synthesized by end-capping of PPRs self-assembled from a distal thiol terminated PEG andα-CDs using admantane derivatives containing both an acrylol or methacrylol group and ATRP initiating site via Michael addition.Secondly,the PR-based copolymers were prepared using the obtained PR-based initiators to initiate ATRP of n-butyl methacrylate（BMA）.It was shown that the control on the number of threadedα-CD was achieved by changing the DMF/H₂O volume ratio in the first step reaction.The tunability of PBMA segment lengths was also preliminarily realized by adjusting the molar feed ratio of BMA.Furthermore,the found number ofα-CDs in PRCos basically kept in agreement with the corresponding PR-based initiators,implying the de-threading problem ofα-CDs solved.Interestingly,these PRCos can be cast into films and electrospun into micro-nano fibers,respectively.In addition,the methylation of PRCos with CH₃I was also carried out to give rise to MePRCos in order to eliminate the hydrogen bond interaction increasing the mobility of threadedα-CDs along the polymeric axis.The dielectric relaxation analysis was employed to investigate the movement behaviors of threadedα-CDs in all PR-based copolymers.The sliding of threaded CDs in both PRCos and MePRCos was clearly visible in a low frequency range,while the rotating of threaded CDs in MePRCo was definitely observed in a high frequency range resulting from the relatively easier molecular mobility after methylation modification.In addition,the PBMA segments in PRCos and MePRCos were noted to impede the motion of threadedα-CDs.The DMA analysis further showed that the mobility ofα-CDs can simultaneously strengthen and toughen the resulting PR-based copolymers.This is the first evidence confirming the presence of sliding and rotating motion of CDs in the solid PR-based film materials,which lays the foundation to extend the application fields from solution and gel to solid states.