Controlled radical polymerization of methyl methacrylate in the presence of palladium acetate, triphenylphosphine, and carbon tetrachloride

in Macromolecules (1997), 30(24), 7631-7633

Controlled radical polymerization of N-Vinylphthalimide using carboxyl-terminated trithiocarbonate as RAFT agent and preparation of microfibers via electrospinning technique

in Journal of Applied Polymer Science (2010), 117(2), 1005-1012

Reversible addition-fragmentation chain transfer (RAFT) polymerization of N-vinylphthalimide in N,N-dimethylformamide (DMF) solution was carried out using 2-carboxypropan-2-yl dodecyl trithiocarbonate as ... [more ▼]

Reversible addition-fragmentation chain transfer (RAFT) polymerization of N-vinylphthalimide in N,N-dimethylformamide (DMF) solution was carried out using 2-carboxypropan-2-yl dodecyl trithiocarbonate as a reversible chain transfer agent in the presence of 2,2-azobisisobutyronitrile. The molecular weights of the polymers increased linearly with the monomer conversion and the molecular weight distributions were relatively narrow (PDI < 1.2). It is confirmed by chain extension reaction that the polymer prepared via RAFT polymerization can be used as a macro-RAFT agent. The structure of both polymers was characterized and confirmed by size-exclusion chromatography and 1H-NMR techniques. Ultrafine microfibers were prepared by electrospinning of poly(N-vinylphthalimide) in DMF solution. The effects of electrospinning process parameters such as voltage, tip-to-collector distance, and solution concentration on the morphology and the average size of the electrospun fibers were studied. To evaluate the fiber diameters, scanning electron microscope micrographs of the microfibers were performed. [less ▲]

Controlled radical polymerization of styrene mediated by the C-phenyl-N-tert-butylnitrone/AIBN pair: Kinetics and electron spin resonance analysis

in Journal of Polymer Science Part A-Polymer Chemistry (2007), 45(7), 1219-1235

Kinetics of the free radical polymerization of styrene at 110 degrees C has been investigated in the presence of C-phenyl-N-tert-butylnitrone (PBN) and 2,2'-azobis(isobutyronitrile) (AIBN) after ... [more ▼]

Kinetics of the free radical polymerization of styrene at 110 degrees C has been investigated in the presence of C-phenyl-N-tert-butylnitrone (PBN) and 2,2'-azobis(isobutyronitrile) (AIBN) after prereaction in toluene at 85 degrees C. The effect of the prereaction time and the PBN/AIBN molar ratio on the in situ formation of nitroxides and alkoxyamines (at 85 degrees C), and ultimately on the control of the styrene polymerization at 110 degrees C, has been investigated. As a rule, the styrene radical polymerization is controlled, and the mechanism is one of the classical nitroxide-mediated polymerization. Only one type of nitroxide (low-molecular-mass nitroxide) is formed whatever the prereaction conditions at 85 degrees C, and the equilibrium constant (K) between active and dormant species is 8.7 x 10(-10) mol L-1 at 110 degrees C. At this temperature, the dissociation rate constant (k(d)) is 3.7 x 10(-3) s(-1), the recombination rate constant (k(c)) is 4.3 x 10(6) L mol(-1) s(-1), whereas the activation energy (E-a,E-diss), for the dissociation of the alkoxyamine at the chain-end is similar to 125 kJ mol(-1). Importantly, the propagation rate at 110 degrees C, which does not change significantly with the prereaction time and the PBN/AIBN molar ratio at 85 degrees C, is higher than that for the thermal polymerization at 110 degrees C. This propagation rate directly depends on the equilibrium constant K and on the alkoxyamine and nitroxide concentrations, as well. [less ▲]

Controlled radical polymerization of vinyl monomers catalyzed by ruthenium N-heterocyclic carbene complexes

in Abstracts of Papers - American Chemical Society, National Meeting (2005), 230

As part of our program devoted to the development of new metal-NHC catalyst systems, we have launched a detailed investigation on the catalytic activity of ruthenium-p-cymene complexes bearing NHC ligands ... [more ▼]

As part of our program devoted to the development of new metal-NHC catalyst systems, we have launched a detailed investigation on the catalytic activity of ruthenium-p-cymene complexes bearing NHC ligands for the ring opening metathesis polymerization (ROMP) of cyclic olefins and for the ATRP of vinyl monomers. We report herein on the use for ATRP of [RuCl2(p-cymene)(NHC)] complexes generated in situ by combining the [RuCl2(p-cymene)]2 dimer with an imidazolium salt and a base such as potassium tert-butoxide, cesium carbonate or aluminum isopropoxide. [less ▲]

Controlled RAFT synthesis of polyacrylonitrile-b-poly(acrylic acid) diblocks as precursors of carbon nanocapsules with assistance of gold nanoparticles

in Chemistry of Materials (2007), 19(9), 2150-2154

A new strategy for the synthesis of carbon nanocapsules has been developed, based on the preparation of well-defined polyacrylonitrile-b-poly(acrylic acid) (PAN-b-PAA) block copolymers followed by their ... [more ▼]

A new strategy for the synthesis of carbon nanocapsules has been developed, based on the preparation of well-defined polyacrylonitrile-b-poly(acrylic acid) (PAN-b-PAA) block copolymers followed by their micellization in basic water to form spherical micelles with a PAN core and PAA shell. The PAN is then cross-linked by the use of gold nanoparticles. After pyrolysis, carbon nanocapsules are produced by graphitization of the PAN core and diffusion of the molten gold nanoparticles out of the nano-objects. [less ▲]

Controlled release of drugs from an original multi-component device

Poster (2007)

Controlled release of drugs from multi-component biomaterials

in Acta Biomaterialia (2008), 4(6), 1788-1796

In order to control their release, drugs are encapsulated into systems which are expected to provide a certain site with a predetermined amount of drug over a well-defined period of time. Here we report ... [more ▼]

In order to control their release, drugs are encapsulated into systems which are expected to provide a certain site with a predetermined amount of drug over a well-defined period of time. Here we report on a multi-component drug delivery biomaterial that consists of a hydrogel matrix in which drug-loaded biodegradable microcarriers are dispersed, and whose potential applications could be found in the design of implantable devices with long-term activity, as required by contraceptive and hormone replacement treatments. The release profile of the drug can actually be tuned by the complex interplay of several release mechanisms, including the permeability and eventually the degradation rate of the microcarriers and the diffusion through the hydrogel. The hydrogel consisted of 2-hydroxyethyl methacrylate cross-linked by ethylene glycol dimethacrylate. The microcarriers were biodegradable poly-ε-caprolactone (PCL) microspheres in which active molecules, such as levonorgestrel (LNG), were encapsulated. The hydrogels were characterized by water swelling, thermal properties, LNG diffusion through drug-free and drug-depleted hydrogel membranes and LNG release from devices with drug dispersed in the hydrogel. The PCL microspheres were observed by scanning electron microscopy; their size distribution, LNG loading and release were also investigated. The hydrogel-microsphere assemblies were characterized in terms of the distribution of the microspheres within the hydrogel, water swelling and the release of the encapsulated molecules. The developed device, due to its composite structure, has the ability to combine several release mechanisms, leading to drug release obeying zero-order kinetics for most of the time. [less ▲]

Controlled reproduction of the chub, Leuciscus cephalus (L.) in captivity.

in De Pauw, N.; Jaspers, E.; Ackefors, H. (Eds.) et al Aquaculture - a biotechnology in progress (1989)

Controlled ring-opening polymerization of epsilon-caprolactone promoted by "in situ" formed yttrium alkoxides

in Macromolecules (2000), 33(5), 1530-1535

The ring-opening polymerization of ε-caprolactone has been initiated by [tris(hexamethyldisilyl)amide]yttrium in the presence of an excess of 2-propanol. This initiating system is very active even at high ... [more ▼]

The ring-opening polymerization of ε-caprolactone has been initiated by [tris(hexamethyldisilyl)amide]yttrium in the presence of an excess of 2-propanol. This initiating system is very active even at high alcohol-to-Y molar ratio. Polymers with controlled molecular parameters (Mn, end groups) and low dispersity are formed as result of fast alkoxide/alcohol exchange. At molar excess of 2-propanol higher than 100, this exchange is no longer quantitative. The in situ formed active species involved in this new initiating system are different from those ones present in the commercial yttrium oxo-isopropoxide Y5(μ-O)(OiPr)13 cluster. Evidence is provided by 1H NMR spectroscopy. [less ▲]

Controlled synthesis and chemical modification of unsaturated aliphatic (co)polyesters based on 6,7-dihydro-2(3H)-oxepinone

in Journal of Polymer Science Part A-Polymer Chemistry (2002), 40(14), 2286-2297

A pure unsaturated cyclic ester, 6,7-dihydro-2(3H)-oxepinone (DHO2), was prepared by a new synthetic route. The copolymerization of DHO2 with epsilon-caprolactone (CL) was initiated by aluminum ... [more ▼]

A pure unsaturated cyclic ester, 6,7-dihydro-2(3H)-oxepinone (DHO2), was prepared by a new synthetic route. The copolymerization of DHO2 with epsilon-caprolactone (CL) was initiated by aluminum isopropoxide [Al(OiPr)3] at 0 °C as an easy way to produce unsaturated aliphatic polyesters with nonconjugated CC double bonds in a controlled manner. The chain growth was living, as certified by the agreement between the experimental molecular weight at total monomer conversion and the value predicted from the initial monomer/initiator molar ratio. The polydispersity was reasonably low (weight-average molecular weight/number-average molecular weight 1.2). The homopolymerization of DHO2 was, however, not controlled because of fast intramolecular transesterification. Copolymers of DHO2 and CL were quantitatively oxidized with the formation of epoxides containing chains. The extent of the epoxidation allowed the thermal properties and thermal stability of the copolyesters to be modulated. The epoxidized copolyesters were successfully converted into thioaminated chains, which were then quaternized into polycations. No degradation occurred during the chemical modification. [less ▲]