The Design And Synthesis Of Poly(rod-coil) Polymers And Their Use In Selective Separation Of Single-walled Carbon Nanotubes

The separation and purification of semiconducting and metallic tubes from single-walled carbon nanotube（SWNT）products is a prerequisite to give them full play of the excellent properties and realization of attractive applications.Among the developed methods,using?-?interactions to selectively encapsulate and solubilize SWNTs has been considered as an efficient,simple and non-destructive way.To date,there are two kinds of reagents,conjugated polymers and small molecules evolved in this separation technology,and each of them has its advantages and disadvantages.Conjugated polymers can provide strong?-?interactions,but it is rigid,complicated,and hard to be designed for specific nanotubes.Conjugated small molecules have defined and clear structures,thus easily correlate with their performances.However,their?-?interactions with SWNTs are weak and separation selectivity is poor,In this work,we propose the use of poly（rod-coil）polymers,which are composed of rigid conjugated segments and flexible non-conjugated segments in an alternative fashion,as a new kind of reagent for selective separation and purification of SWNTs.First of all,we designed and synthesized poly（rod-coil）polymer P4,P8,P12 and P16 and fully conjugated polymer P0 in our work,The structures of P4,P8,P12 and P16 are composed of a p-phenylene（via 1,4-connecting）and two fluorene dimer flanked conjugated segments and a flexible alkylene diacetate bearing 4,8,12,and 16carbon numbers,respectively,while P0 does not contain any non-conjugated alkylene diacetate in the backbone.It was found that the introduction and length of flexible segments have great impacts on the separation performance.When feeding the polymer/SWNT ratio was 3/1,the separated carbon nanotubes by P16 displayed a near-infrared absorption band(S₂₂)with an integrated area of 119.9.In comparison,the separated carbon nanotubes by poly（9,9-dioctylfluorene）（PFO）and fully conjugated polymer P0 only showed 8.63 and 69.5 for their S22 bands,respectively.Obviously,the separation performance of P16 is much better than PFO and P0.Meanwhile,P8 also displayed a superior performance to PFO,whereas P4 and P12were inferior.Secondly,the effect of molecular weight on the separation performance of the polymers was investigated.Two batches of P8 polymers（P8-HW and P8-LW）with average molecular weights of P10 and 5-6 kDa respectively,were prepared and used for solubilizing SWNTs.The results showed that P8-HW has much higher encapsulating capabilities than P8-LW,indicating the importance of the molecular weight.Thirdly,we also prepared polymer P8-m,which has a similar chemical structure as P8 except the center unit in rigid conjugated segments is changed from p-phenylene（1,4-connecting mode）to m-phenylene（1,3-connecting mode）.Under the similar molecular weight in the range of 5-6 kDa,P8-m was found to exhibit much better encapsulation performance than P8.The above results undoubtedly demonstrate that poly（rod-coil）polymers are excellent reagents for carbon nanotube separation and purification.The length,molecular weight and skeleton of conjugated and nonconjugated segments are very important to their encapsulation performances.