Functionalization Of Cyclodextrin Via Cyclodextrin Xanthate Mediated RAFT Polymerization

Cyclodextrin (CD) has a cone-shaped structure, which process a hydrophobic cavity and a hydrophilic outside. Cyclodextrin and its derivatives have attracted significant interest of researcher to construct artificial enzymes, molecule recognition sensors and other functional models. Polymers containing cyclodextrin units are attractive because of the combination of both the special characters of cyclodextrin and polymers.In this paper, cyclodextrin xanthate is synthesized, and the properties of cyclodextrin xanthate as chain transfer reagents for reversible addition-fragmentation chain transfer polymerization (RAFT) are studied. Two water-soluble monomers, N,N-dimethylacrylamide and N-isopropylacrylamid were used to graft ontoβ-cyclodextrin throught cyclodextrin xanthate mediated RAFT polymerization.Cyclodextrin xanthate was prepared. β-Cyclodextrin reacted with carbon disulfide in aqueous alkaline solution to produce sodium cyclodextrin xanthate, then esterified with methyl 2-bromobutyrate. The structures of the cyclodextrin xanthate were characterized by using 1H NMR and 13C NMR. The results indicated that three 6-hydroxy groups of one cyclodextrin ring were xanthated, and the degree of substitution is 0.45.Cyclodextrin xanthate was used as the RAFT reagent from which N,N-dimethylacrylamide (DMA) was initiated and grafted onto cyclodextrin. The structures of the graft copolymers were characterized by using NMR. The viscosity, surface tension and circular dichroism of the graft copolymers were also studied. The morphology of the self-assemblies was studied by high-resolution transmission electron microscopy. The results indicated that the graft copolymer was a crown-like molecule. The GPC results showed that all the graft copolymers had narrow molecular weight distribution that was characteristics of controlled polymerization. The chains of the graft copolymer molecules were fully extended in aqueous solution at low concentration, while they aggregated to form nano-spheres with a diameter of about 6 nm.Cyclodextrin xanthate was also used to prepare the graft polymerization of N-isopropylacrylamide to give copolymer CD-PNIPAM. The molecular weight and molecular weight distribution were characterized by using NMR and GPC. Cyclodextrin xanthate mediated polymerization showed the first order kinetics that was characteristics of"living"/controlled manner. The low critical solution temperature(LCST) was measured through visible transmittance of copolymer in aqueous solution using UV-Vis absorption spectra. The particle diameter and distribution of CD-PNIPAM in aqueous was studied at different temperature before and after LCST. The result showed that the monomolecular chain exists at low temperature, and particle diameter are about 2.6nm, while above LCST, the segment of NIPAM precipitated from the aqueous solution, and aggregated. Thus particle diameters increased to 99 nm.