In situ nitroxide-mediated polymerization of styrene promoted by the N-tert-butyl-alpha-isopropylnitrone/BPO pair: ESR investigations

in Journal of Polymer Science. Part A-1, Polymer Chemistry (2013), 51(8), 1786-1795

The styrene polymerization initiated by benzoyl peroxide (BPO) in the presence of N-tert-butyl--isopropylnitrone as nitroxide precursor is well-controlled provided that a prereaction between the nitrone ... [more ▼]

The styrene polymerization initiated by benzoyl peroxide (BPO) in the presence of N-tert-butyl--isopropylnitrone as nitroxide precursor is well-controlled provided that a prereaction between the nitrone and BPO is carried out in suitable conditions prior to polymerization at a higher temperature. Electron spin resonance (ESR) spectroscopy was implemented to probe the nitroxides formed during both steps, that is, the prereaction and polymerization, and to get crucial information regarding the structure of the nitroxides responsible for the polymerization control. ESR studies combined with first principles calculations have evidenced that nitroxides observed during the prereaction in the presence of styrene and during the polymerization steps consist of a mixture of two macronitroxides. One is formed by the addition of a growing polystyrene chain to the nitrone as would be expected. However, the second one results from the addition of a polystyrene chain to tert-butyl nitroso that is in situ formed presumably by decomposition of the first macronitroxide type. [less ▲]

Convenient grafting through approach for the preparation of stealth polymeric blood pool magnetic resonance imaging contrast agents

in Journal of Polymer Science. Part A-1, Polymer Chemistry (2011), 49(17), 3700-3708

New hydrosoluble magnetic resonance imaging (MRI) macrocontrast agents are synthesized by reversible addition fragmentation chain transfer (RAFT) copolymerization of poly(ethylene oxide) methyl ether ... [more ▼]

New hydrosoluble magnetic resonance imaging (MRI) macrocontrast agents are synthesized by reversible addition fragmentation chain transfer (RAFT) copolymerization of poly(ethylene oxide) methyl ether acrylate (PEOMA) with an acrylamide bearing a ligand for gadolinium, followed by the complexation of Gd3+. This convenient and simple grafting through approach leads to macrocontrast agents with a high relaxivity at high frequency that is imparted by the restricted tumbling of the Gd3+ complex caused by its attachment to the polymer backbone. Importantly a very low protein adsorption is also evidenced by the hemolytic CH50 test. It is the result of the poly(ethylene oxide) (PEO) brush that efficiently hides the gadolinium complex and renders it stealth to the proteins of the immune system. Improved contrast and long blood circulating properties are thus expected for these macrocontrast agents. [less ▲]

Pegylated thermally responsive block copolymer micelles and nanogels via in situ RAFT aqueous dispersion polymerization

in Journal of Polymer Science. Part A-1, Polymer Chemistry (2009), 47(9), 2373-2390

A very straightforward approach was developed to synthesize pegylated thermoresponsive core-shell nanoparticles in a minimum of steps, directly in water. It is based on RAFT-controlled radical ... [more ▼]

A very straightforward approach was developed to synthesize pegylated thermoresponsive core-shell nanoparticles in a minimum of steps, directly in water. It is based on RAFT-controlled radical crosslinking copolymerization of N,N-diethylacrylamide (DEAAm) and N,N-methylene bisacrylamide (MBA) in aqueous dispersion polymerization. Because DEAAm is water-soluble and poly(N,N-diethylacrylamide) (PDEAAm) exhibits a lower critical solution temperature at 32 °C, the initial medium was homogeneous, whereas the polymer formed a separate phase at the reaction temperature. The first macroRAFT agent was a surface-active trithiocarbonate based on a hydrophilic poly(ethylene oxide) block and a hydrophobic dodecyl chain. It was further extented with N,N-dimethylacrylamide (DMAAm) to target macroRAFT agents with increasing chain length. All macroRAFT agents provided excellent control over the aqueous dispersion homopolymerization of DEAAm. When they were used in the radical crosslinking copolymerization of DEAAm and MBA, the stability and size of the resulting gel particles were found to depend strongly on the chain length of the macroRAFT agent, on the concentrations of both the monomer and the crosslinker, and on the process (one step or two steps). The best-suited experimental conditions to reach thermosensitive hydrogels with nanometric size and well-defined surface properties were determined. [less ▲]

New antibacterial cationic surfactants prepared by Atom Transfer Radical Polymerization

in Journal of Polymer Science. Part A-1, Polymer Chemistry (2006), 44(3), 1214-1224

Efficient antibacterial surfactants have been prepared by the quaternization of the amino groups of poly(ethylene-co-butylene)-b-poly[2-(dimethylamino)ethylmethacrylate] (PEB-b-PDMAEMA) diblock copolymers ... [more ▼]

Efficient antibacterial surfactants have been prepared by the quaternization of the amino groups of poly(ethylene-co-butylene)-b-poly[2-(dimethylamino)ethylmethacrylate] (PEB-b-PDMAEMA) diblock copolymers by octyl bromide. The diblock copolymers have been synthesized by ATRP of 2-(dimethylamino)ethylmethacrylate (DMAEMA) initiated by an activated bromide-end-capped poly(ethylene-co-butylene). In the presence of CuBr, 1,4,7,10,10-hexamethyl-triethylenetetramine (HMTETA), and toluene at 50 °C, the initiation is slow in comparison with propagation. This situation has been improved by the substitution of CuCl for CuBr, all the other conditions being the same. Finally, the addition of an excess of CuCl2 (deactivator) to the CuCl/HMTETA catalyst is very beneficial in making the agreement between the theoretical and experimental number-average molecular weights excellent. The antibacterial activity of PEB-b-PDMAEMA quaternized by octyl bromide has been assessed against bacteria and is comparable to the activity of a commonly used disinfectant, that is, benzalkonium chloride. [less ▲]