Covalent Functionalization Of MultiWalled Carbon Nanotubes With Thermoresponsive Polymers

In this paper, covalent functionalization of alkyne-decorated multiwalled carbon nanotubes (MWNTs) with azide-derivatized, thermoresponsive diblock copolymer, poly(N,N-dimethylacrylamide)-poly(N-isopropylacryl amide) (PDMA-PNIPAM), was accomplished by"Click"coupling through"grafting to"technique. Crosslinked micelles, (PDMA-co-PNAS)-b-PNIPAM and PDMA-b-(PNIPAM-co-PNAS), was achieved via the reaction of N-acryloxysuccinimide (NAS) residues with ethylene diamine after copolymerization of DMA or NIPAM with the NAS. The crosslinked micelles grafting to the MWNT surface was also fulfilled by"Click"coupling. The main contents were as follows:The preparation of block copolymers. PDMA-PNIPAM block coplymers with different PNIPAM block length were synthesized through RAFT polymerization using azide functionized trithiocarbonates (EMP-N3) as chain transfer agent. (PDMA-co-PNAS)-b-PNIPAM and PDMA-b-(PNIPAM-co-PNAS) copolymers were also synthesized by RAFT copolymerization of the corresponding DMA or NIPAM monomers with NAS, respectively, followed by chain extension. The effects of PNIPAM block length as well as the incorporation of NAS unit on the copolymer thermoresponsibility have been investigated. The DLS results indicate that the copolymer show decreasing critical micelle temperature (CMT) as the PNIPAM block length and polymer aqueous concentration increase, and also the incorpration of NAS unit into PNIPAM block."Click"coupling between alkyne functionalized MWNTs and reactive micelles. The hydroxyl functionalized MWNTs was firstly treated with toluene 2,4-diisocyanate (TDI) follwed by propargyl alcohol to produce alkyne-functionalized MWNTs. Covalent functionalization of MWNTs with PDMA-PNIAPM was accomplished by"Click"coupling between MWNTs surface alkyne and polymer end azide groups. The effects of micellization of the diblock copolymer on the polymer grafting density have been investigated. TGA and UV-Vis analysis suggested that the bonding density of grafted polymerscould be increased when the reaction was conducted above the CMT. SEM was utilized to demonstrate that the coupling reaction was carried out between micelles and MWNTs. Polymer-MWNTs conjugates were characterized by TEM, which indicating that the polymer was covalently bounded to the carbon nanotubes. Functionalization of MWNTs with crosslinked micelles. (PDMA-co-PNAS)-b- PNIPAM and PDMA-b-(PNIPAM-co-PNAS) crosslinked micelles were prepared with ethylene diamine as crosslinking agent. Subsequently, the crosslinked micelles were grafted to MWNTs surface through"Click"coupling. The effects of micelle crosslinking approache on the micellar diameter as well as the thermoresponsibility, the effects of shell or core crosslinked micelles on the micelle grafting density of micelle-functionalized MWNTs have been investigated. DLS results indicated that core crosslinked micelles have a diameter of about 40 nm, and the shell crosslinked micelles have thermoresponsibility. TGA and SEM measurements implyed that the micelle content of micelle-functionalized MWNTs was increased when core crosslinked micelles were used in the coupling system. The functionalized tubes exhibited high solubility in solvents, such as methanol and water, and the solutions remained stable for at least 2 months.