Linear Macrocyclic Polymer Based On Pillar[6]Arene

The introduction of supramolecular macrocycles into the polymers by covalent binding can not only retain the stability and processability of traditional polymers,but also provide multiple complex sites,which can be used to construct more novel materials with special structures and properties.In recent years,pillararenes have attracted much attention due to their unique advantages of highly symmetric pillar-shaped structure,electron-rich cavities,and easy derivatization.Most of the reported polymers containing pillararenes are prepared by side-group polymerization,although these polymers exhibit more excellent properties,the flexible chains on the polymer usually block or interpenetrating the cavity of pillararenes,which make it difficult to achieve the maximum functional utilization of pillararenes on polymers.Inspired by the above background,we developed a strategy for the preparation of linear macrocyclic polymers with pillar[6]arenes as the main chains by cyclization polymerization,and characterized its microstructure,thermodynamics properties,and host-guest chemistry.Preparation and characterization of linear macrocyclic polymers based on pillar[6]arene:firstly,we have synthesized the compound 4 as the precursor for constructing linear macrocyclic polymers,and then reacted with paraformaldehyde under the catalysis of the trifluoroacetic acid to prepare the linear macrocyclic polymers based on pillar[6]arene.The molecular structure of monomers was characterized by Nuclear Magnetic Resonance(NMR)and Mass Spectrometry(MS).The molecular weight of the polymers was characterized by Gel Permeation Chromatography(GPC).In addition,the microstructure of linear macrocyclic polymers was obtained by Atomic Force Microscopy(AFM)as bead-on-string nanofibers.The results of thermal gravimetric analysis(TGA)and differential scanning calorimetry(DSC)show that the polymers have good thermal stability,and its remarkable glass transition process further confirms that we have successfully prepared linear macrocyclic polymers.Host-Guest properties of linear macrocyclic polymer based on pillar[6]arene:The host-guest chemistry of linear macrocyclic polymer(PP[6])based on pillar[6]arene was investigated by ~1H NMR titration experiments using 1-butylpyridinium bromide(G1)and p-phenylenediacetonitrile(G2).The results of titration results and Hill equation also show that all pillar[6]arenes in linear macrocyclic polymer(PP[6])can complex with guest.In addition,when the PP[6]complex with different guests,one of the sites occupied by the guest will not affect the subsequent sites.According to all results,it can be concluded that the pillar[6]arene cavities in the linear macrocyclic polymers show non-interference with each other,which is consistent with the properties of the monomer.Furthermore,comparing the complexation results of Et-P[6]with different guests(G1,G2)can further indicate that the linear macrocyclic polymer(PP[6])exhibits the equivalent characteristics as the monomer.