Synthesis And Characterization Of Phenylboronate-Diol Crosslinked Polymer/SWCNTs Hybrid Gels

It is well known that phenylboronic acid derivatives can bind diols throughreversible boronate ester formation, so it can be used to detection, separation andpurification of the carbohydrates. As one of the dynamic covalent bonds, the glucose-,pH-responsive boronate ester bond has been successfully used to prepare smartpolymer gels, which have many potential applications in the fields of self-regulatedinsulin delivery, separation, and sensor systems.Recently, polymer gels hybridized with carbon nanotubes (CNTs) have drawnconsiderable research interest because the combination of CNTs with a polymermatrix is expected to improve the mechanical properties of the polymer gels. In thiswork phenylboronic acid-and diol-containing polymers were separately prepared bythe reversible addition-fragmentation chain transfer (RAFT) polymerization. Covalentfunctionalization of SWCNTs with azide-derivatized, diol-containing polymer wasthen accomplished by a nitrene addition reaction (f-SWCNTs). Subsequently, thereversible hybrid gels were prepared by crosslinking phenylboronic acid-containingpolymer with the matrix of diol-containing polymer and f-SWCNTs. The main resultsare shown as follows:(1) The phenylboronic acid-and diol-containing polymers were separatelyprepared by the RAFT polymerization. The molecular weight and polydispersity ofpolymers were characterized by GPC. The data of GPC indicated that both of the twopolymers had a narrow molecular distribution.(2) Synthesis of f-SWCNTs. Covalent functionalization of SWCNTs withazide-derivatized, diol-containing polymer was accomplished by a nitrene additionreaction. The f-SWCNTs product was characterized by Raman, FTIR and TGA. Bythe analysis above it is concluded that the polymer had been grafted to the surface ofSWCNTs, and the TGA data indicated that the mass loss was around27wt%.(3) Preparation of hybrid gel by crosslinking of poly(VPB-co-DMA), PHBA, andf-SWCNTs. Analysis of the composition-property relationships of these polymerhybrid gels, specifically considering the effects of pH, molar ratio of HBA to VPBunits, f-SWCNTs concentrations, and gelator concentrations on dynamic rheologicalproperties, were performed. It is found that the hybrid gel was formed when pH valuewas between3.9-7.0. With the molar ratio of HBA/VPB increasing from2:1to5:1, both of the relaxation time and G’ seemed a tendency of declining due to the decreaseof the crosslinking density. On the other hand, G’ increased with the increasing off-SWCNTs or gelator concentration in the hybrid gels. Additionally, the hybrid gelscan be switched into their starting polymer solution by adjusting pH of the system.The reversible sol-gel phase transition can be performed for several cycles in a similarway of supramolecular gel. Moreover, the hybrid gel revealed interesting self-healingproperty, which occurred autonomously with out any outside intervention.