Solubilization of C₆₀ by micellization with a thermoresponsive block copolymer in water: Characterization, singlet oxygen generation, and DNA photocleavage

Abstract

Water‐soluble diblock copolymer, poly(N‐isopropylacrylamide)‐block‐poly(N‐vinyl‐2‐pyrroridone) (PNIPAMm‐b‐PNVPn), was found to associate with fullerene (C60), and thus C60 can be solubilized in water. The 63C60/PNIPAMm‐b‐PNVPn micelle formed a core‐shell micelle‐like aggregate comprising a C60/PNVP hydrophobic core and a thermoresponsive PNIPAM shell. The C60‐containing polymer micelle formation and its thermoresponsive behavior were characterized using light scattering and 1H NMR techniques. The hydrodynamic radius (Rh) of the C60‐bound polymer micelle increased with increasing temperature, which was ascribed to the hydrophobic association between dehydrated PNIPAM shells above lower critical solution temperature (LCST). 1H NMR data suggest that the motion of the PNIPAM block is restricted above LCST due to the dehydration of the PNIPAM shell in water. The generation of singlet oxygen by photosensitization by the C60‐bound polymer micelle was confirmed from photooxidation of 9,10‐anthracenedipropionic acid. Furthermore, DNA was found to be cleaved by visible light irradiation in the presence of the C60‐bound polymer micelle. Therefore, there may be a hope for a pharmaceutical application of the C60‐bound polymer micelle to cancer photodynamic therapy. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011.

Living Radical Polymerization by the RAFT Process – A Third Update

“…With trithiocarbonate (155), while the polymerization showed some living character, conversions were low and dispersities were poor ( . 1.5) and the latter increased with monomer conversion.…”

“…[185] polymerization of MA with cyclic RAFT agent 444 and either ethyl 2-bromopropionate or 2-diethyl, meso-2,5-dibromoadipate as initiator and CuBr/tris[(2-pyridyl) methyl]amine catalyst. [563] RAFT Agent Stability During RAFT Polymerization Li et al [221] have reported that some trithiocarbonate RAFT agents (18,89,155) are unstable during polymerization of DMAEA at 808C in DMF. The RAFT agents were stable during BA and St polymerization under similar conditions and a lower rate of degradation was observed in the case of DMAEA/St copolymerizations.…”

“…The most recent work used xanthate (229) [113,506] or trithiocarbonate (155). [440] RAFT polymerization with xanthate (229) was controlled although dispersities were broad.…”

“…Thus, changes in UV-visible spectra on conversion of an initial RAFT agent to a macro-RAFT agent need to be considered when using spectrophotometry to follow the course of RAFT polymerization. The crystal structure of the RAFT agent 2-[(dodecylsulfanyl)carbonothioylsulfanyl] propanoic acid (155) has been published. [555] Two reviews contain significant reference to RAFT synthesized polymers.…”

“…[148] Polymerization Mediated by Organotellurium, Organobismuthine, and Organostibine Reagents The mechanism and application of radical polymerization mediated by organotellurium (TERP), organobismuthine, and organostibine compounds has been reviewed. [149,150] Recent papers have described the use of TERP in surfactant-free emulsion polymerization of BA [151] and St, [152,153] the preparation of polymer monoliths based on crosslinked poly (Am), [154] the use of poly(NIPAm)-b-poly(NVP) for solubilization of C 60 , [155] the use of heteroatom-metal exchange reactions in end-group transformation of polymers (poly(BA), poly (MMA), poly(HEMA), poly(NIPAm)) in organostibine or organobismuth-mediated polymerization [156] and the use of organostibine-mediated polymerization in St/MMA copolymerization. [157] The end-groups of methacrylic polymers (poly(BA), poly (MMA), poly(HEMA), poly(MAN)) formed by TERP or organostibine-mediated polymerization can be eliminated to form macromonomers in high yield through reaction with (2,2,6,6-tetramethylpiperidinyl-1-oxy (TEMPO) (and formation of an alkoxyamine intermediate) or the addition-fragmentation chain transfer agent, ethyl 2-[(tributylstannyl)methyl]acrylate.…”