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New biodegradable multiblock amphiphilic and thermosensitive poly(ether ester urethane)s consisting of poly[(R)-3-hydroxybutyrate] (PHB), poly(ethylene glycol) (PEG), and poly(propylene glycol) (PPG) blocks were synthesized, and their aqueous solutions were found to undergo a reversible sol-gel transition upon temperature change at very low copolymer concentrations. The multiblock poly(ether ester urethane)s were synthesized from diols of PHB, PEG, and PPG using 1,6-hexamethylene diisocyanate as a coupling reagent. The chemical structures and molecular characteristics of the copolymers were studied by GPC, 1H NMR, 13C NMR, and FTIR. The thermal stability of the poly(PEG/PPG/PHB urethane)s was studied by thermogravimetry analysis (TGA), and the PHB contents were calculated based on the thermal degradation profile. The results were in good agreement with those obtained from the 1H NMR measurements. The poly(PEG/PPG/ PHB urethane)s presented better thermal stability than the PHB precursors. The water soluble poly(ether ester urethane)s had very low critical micellization concentration (CMC). Aqueous solutions of the new poly(ether ester urethane)s underwent a sol-gel-sol transition as the temperature increased from 4 to 80 degrees C, and showed a very low critical gelation concentration (CGC) ranging from 2 to 5 wt %. As a result of its multiblock architecture, a novel associated micelle packing model can be proposed for the sol-gel transition for the copolymer gels of this system. The new material is thought to be a promising candidate for injectable drug systems that can be formulated at low temperatures and forms a gel depot in situ upon subcutaneous injection.

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The incorporation of carbon nanotubes to a polymer generally improves the stiffness and strength of the polymer, but the ductility and toughness of the polymer are compromised in most cases. Here we report the mechanical reinforcement of polyethylene (PE) using polyethylene‐grafted multiwalled carbon nanotubes (PE‐g‐MWNTs). The stiffness, strength, ductility and toughness of PE are all improved by the addition of PE‐g‐MWNTs. The grafting of PE onto MWNTs enables the well‐dispersion of nanotubes in the PE matrix and improves MWNT/PE interfacial adhesion. The grafting was achieved by a reactive blending process through melt blending of PE containing 0.85 wt % of maleic anhydride and amine‐functionalized MWNTs. The reaction between maleic anhydride and amine groups, as evidenced by X‐ray photoelectron spectroscopy and Raman spectroscopy, leads to the grafting of PE onto the nanotubes.

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The functionalization of carbon nanotubes (CNTs) has been carried out in various ways for numerous applications in biotechnology, [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15] including for the preparation of sensors, [2,3] as scaffolds for cell growth, [4] imaging reagents, [5] and transporters for drug delivery. [6-8, 13, 15] One way is to immobilize DNA onto the surface of CNTs through noncovalent interactions [8][9][10][11][12][13] or covalent bonds. [3,[12][13][14][15] Covalent-bond approaches might compromise and even spoil the functions of DNA owing to chemical reactions and the difficulty in releasing DNA. [13, 14b, 15] Nevertheless, noncovalent approaches developed to date may only provide metastable immobilization of DNA onto the surface of CNTs. It was reported that the migration of DNA linked covalently to CNTs was retarded in gel electrophoresis but noncovalent interactions between DNA and CNTs did not completely prevent migration.[14b] Polyethylenimine (PEI) is a type of polymer with a high density of amines, thus DNA may be immobilized securely onto the surface of multiwalled carbon nanotubes (MWNTs) that have been functionalized with PEI through strong electrostatic interactions arising from these amines. Hence, we have adopted a grafting-from approach to prepare polyethylenimine-graft multiwalled carbon nanotubes (PEIg-MWNTs). DNA has been immobilized securely onto the surface of PEI-g-MWNTs as demonstrated by the total inhibition of the migration of DNA in gel electrophoresis, and PEI-g-MWNTs showed transfection efficiency for delivery of DNA that was similar to or even several times higher than that of PEI (25 K) and several orders of magnitude higher than that of naked DNA.PEI was grafted onto the surface of MWNTs by performing a cationic polymerization of aziridine in the presence of amine-functionalized MWNTs (NH 2 -MWNTs). NH 2 -MWNTs were obtained by introducing carboxylic acid groups onto the surface of MWNTs by heating at reflux in 3.0 m nitric acid. The carboxylic acid groups were transformed into acyl chloride groups by treatment with thionyl chloride [16] followed by treatment with ethylenediamine.[14] The grafting of PEI was realized through two mechanisms, the activated monomer mechanism (AMM) or the activated chain mechanism (ACM), by which protonated aziridine monomers or the terminal iminium ion groups of propagation chains, respectively, are transferred to amines on the surface of MWNTs.[17] (see Supporting Information.) The relative amount of PEI grafted onto the surface of MWNTs was investigated by thermogravimetric analysis (TGA) performed under nitrogen. MWNTs were thermally stable up to 600 8C (Figure 1 A, curve a) whereas pure PEI degraded completely at about 500 8C (Figure 1 A, curve d). At 500 8C, pristine MWNTs, NH 2 -MWNTs, and PEI-g-MWNTs showed negligible, about 2.3 %, and 10.5 % weight losses, respectively, thus PEI-g-MWNTs contained about 8.2 % PEI. Grafting with PEI made PEI-g-MWNTs easy to disperse in water, and the resulting suspension was still stable a...

Cationic supramolecules composed of multiple oligoethylenimine‐grafted β‐cyclodextrins that are threaded and blocked on a triblock copolymer chain (see figure) are synthesized as gene‐delivery vectors. The supramolecules contain many cationic cyclic units threaded on a polymer chain to form an integrated entity, functioning as a macromolecular gene vector with good DNA binding ability, low cytotoxicity, and high gene‐transfection efficiency.

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