Self-organization of water-soluble complexes of a poly(2-vinylpyridinium)-block-poly(ethylene oxide) diblock with fluorinated anionic surfactants

in Macromolecules (2003), 36(8), 2579-2581

Probing the stereoselectivity of the ruthenium-catalyzed ring-opening metathesis polymerization of norbornene and norbornadiene diesters

in Macromolecules (2003), 36(5), 1446-1456

The ring-opening metathesis polymerization (ROMP) of two optically active 2,3-dicarboalkoxynorbornadienes derived from (S)-(-)-2-methyl-1-butanol and (R)-(-)-2-butanol were carried out in the presence of ... [more ▼]

The ring-opening metathesis polymerization (ROMP) of two optically active 2,3-dicarboalkoxynorbornadienes derived from (S)-(-)-2-methyl-1-butanol and (R)-(-)-2-butanol were carried out in the presence of the [RuCl2(P-cymene)](2) catalyst precursor activated by trimethylsilyldiazomethane (TMSD). H-1 and C-13 NMR analyses showed that a high degree of stereoregularity was achieved, and homonuclear proton-proton COSY spectroscopy indicated that the major trans fractions of the polymers were most likely isotactic, while the minor cis fractions were syndiotactic. Ring-opened metathesis polymers were also made from 2,3-dicarbomethoxynorbornadiene and exo,exo-2,3-dicarbomethoxy-5-norbornene. They were hydrogenated into the corresponding polynorbornanes using diimide. The NMR spectra of the reduced materials confirmed that the unsaturated parent polymers had an all-trans highly isotactic microstructure. A tentative mechanism involving arene loss, carbene formation, and monomer chelation is proposed to account for the observed stereoselectivities. [less ▲]

Poly(epsilon-caprolactone)/clay nanocomposites by in-situ intercalative polymerization catalyzed by dibutyltin dimethoxide

in Macromolecules (2002), 35(22), 8385-8390

Poly(epsilon-caprolactone)/clay nanocomposites were prepared by in-situ ring-opening polymerization of epsilon-caprolactone by using dibutyltin dimethoxide as an initiator/catalyst. A nonmodified Na ... [more ▼]

Poly(epsilon-caprolactone)/clay nanocomposites were prepared by in-situ ring-opening polymerization of epsilon-caprolactone by using dibutyltin dimethoxide as an initiator/catalyst. A nonmodified Na+-montmorillonite and two montmorillonites surface-modified by dimethyl 2-ethylhexyl (hydrogenated tallow alkyl) and methyl bis(2-hydroxyethyl) (hydrogenated tallow alkyl) ammonium cations, respectively, were used. The evolution of molecular weights was followed in relation to silicate surface modification and clay concentration. The alcohol-bearing organo-modified clay was a co-initiator for the polymerization reaction and thus controlled the molecular weight of the PCL chains. Furthermore, the number-average molecular weight of the growing PCL chains linearly increased with the monomer conversion. Nanocomposites were analyzed by small-angle X-ray diffraction, transmission electron microscopy, and thermogravimetry. The clay dispersion depended on the structure of the alkylammonium used to make the clay more hydrophobic. Exfoliated nanocomposites were formed when hydroxyl-containing alkylammonium. was used; otherwise, intercalated structures were reported. Thermogravimetric analyses showed a higher degradation temperature for the exfoliated structures than for the intercalated ones, both of them exceeding the degradation temperature of unfilled poly(epsilon-caprolactone). [less ▲]

Controlled nitroxide-mediated radical polymerization of styrene, styrene/acrylonitrile mixtures, and dienes using a nitrone

in Macromolecules (2002), 35(19), 7214-7223

Radical polymerization of styrene and copolymerization of styrene and acrylonitrile (60/40) are controlled when conducted in the presence of N-tert-butyl-alpha-isopropylnitrone, which is easily ... [more ▼]

Radical polymerization of styrene and copolymerization of styrene and acrylonitrile (60/40) are controlled when conducted in the presence of N-tert-butyl-alpha-isopropylnitrone, which is easily synthesized from cheap reagents. However, for the control to be effective, the nitrone has to be prereacted with the radical initiator. Nitroxides are then formed "in situ", such that this nitrone system is an attractive alternative for the classical nitroxide-mediated polymerization (NMP), which may require a multistep synthesis of nitroxides or alkoxyamines. The choice of the radical initiator is important because it dictates the structure of the nitroxide and thus its capacity to control the radical polymerization. Well-defined poly(styrene)-b-poly(styrene-co-acrylonitrile), poly(styrene)-b-poly(n-butyl acrylate), and poly(styrene)-b-poly(isoprene) copolymers have been successfully synthesized by this process. [less ▲]

Control of the radical polymerization of tert-butyl methacrylate in water by a novel combination of sodium nitrite and iron(II) sulfate

in Macromolecules (2002), 35(5), 1611-1621

Addition of iron(II) sulfate to sodium nitrite is a new way to control the radical polymerization of tert-butyl methacrylate (tBMA) in water at 80 degreesC. Nitric oxide is released in the reaction medium ... [more ▼]

Addition of iron(II) sulfate to sodium nitrite is a new way to control the radical polymerization of tert-butyl methacrylate (tBMA) in water at 80 degreesC. Nitric oxide is released in the reaction medium as result of the reduction of sodium nitrite by FeSO4. This reaction is of utmost importance because three repeated additions of an alkyl radical to nitric oxide leads to the formation of nitroxide radicals. The basic mechanism for the control of the radical polymerization is thus a nitroxide-mediated process. [less ▲]

pH-dependent micellization of poly(2-vinylpyridine)-block-poly((dimethylamino) ethyl methacrylate) diblock copolymers

in Macromolecules (2001), 34(21), 7435-7440

A series of poly(2-vinylpyridine)-block-poly((dimethylamino)ethyl methacrylate) diblock copolymers (P2VP-b-PDMAEMA) have been synthesized by living anionic polymerization of the comonomers. Dynamic light ... [more ▼]

A series of poly(2-vinylpyridine)-block-poly((dimethylamino)ethyl methacrylate) diblock copolymers (P2VP-b-PDMAEMA) have been synthesized by living anionic polymerization of the comonomers. Dynamic light scattering (DLS) has been used to study the associative behavior of these copolymers in water as a function of copolymer composition, pH, ionic strength, and temperature. Three association regimes are observed. At low pH, loose aggregates are formed, although both the P2VP and PDMAEMA blocks are protonated. At intermediate pH, micelles are observed that consist of an uncharged hydrophobic P2VP core surrounded by a protonated PDMAEMA corona. At higher pH, the PDMAEMA corona is essentially uncharged and collapses at temperatures higher than 40 °C, which results in unstable micelles. The micelles observed by transmission electron microscopy are spherical. [less ▲]

Living ring-opening (co)polymerization of 6,7-dihydro-2(5H)-oxepinone into unsaturated aliphatic polyesters

in Macromolecules (2001), 34(17), 5806-5811

Homopolymerization of the unsaturated cyclic ester, 6,7-dihydro-2(5H)-oxepinone (DHO), and copolymerization with epsilon-caprolactone (epsilon-CL) are an easy way to produce unsaturated aliphatic ... [more ▼]

Homopolymerization of the unsaturated cyclic ester, 6,7-dihydro-2(5H)-oxepinone (DHO), and copolymerization with epsilon-caprolactone (epsilon-CL) are an easy way to produce unsaturated aliphatic polyesters in a controlled manner, Polymerization of DHO initiated by Al((OPr)-Pr-i)(3) in toluene at room temperature proceeds by a coordination-insertion mechanism and is living as certified by the agreement between the experimental molecular weight at total monomer conversion and the value predicted from the initial monomer to initiator molar ratio. The polydispersity is also low (Mw/Mn less than or equal to 1.2). Random copolymerization of DHO and epsilon-CL leads to the same conclusion. Beyond the complete monomer conversion, the poly(DHO) chains experience mainly intermolecular transesterification reactions at the same rate as poly(epsilon CL) under the same conditions. The livingness of the ROP of both DHO and epsilon-CL allows diblock copolymers to be synthesized with predicted composition and molecular weight. Homopoly(DHO) is semicrystalline with Tm at 35°C and Tg at -50°C. Tm and thermal stability can be modulated by copolymerization of DHO with epsilon-CL. [less ▲]

Probing thermoplastic matrix-carbon fiber interphases. 1. Preferential segregation of low molar mass chains to the interface

in Macromolecules (2001), 34(11), 3725-3729

The molecular mobility of polystyrene (PS) chains near the surface of carbon fibers was investigated. The glass transition temperature of very thin coatings deposited on carbon fibers was measured by ... [more ▼]

The molecular mobility of polystyrene (PS) chains near the surface of carbon fibers was investigated. The glass transition temperature of very thin coatings deposited on carbon fibers was measured by supported DMTA in order to probe the properties of the thermoplastic interphase. Depending on the fiber impregnation method from the melt or from solution, Tg changed in an opposite way for the thinnest coatings, decreasing with coating thickness in the case of impregnation in the melt and increasing when a polymer solution was used. This observation is explained by degradation of PS in the melt and subsequent preferential segregation of low molar mass chains to the interface. This conclusion is supported by the study of the Tg of coatings made from a bimodal molar mass distribution. [less ▲]

Morphology of Water-Soluble Interpolyelectrolyte Complexes Formed by Poly(2-vinylpyridinium)-block-poly(ethylene oxide) Diblocks and Poly(4-styrenesulfonate) Polyanions

in Macromolecules (2001), 34(9), 2745-2747

Reactive compatibilization of SAN/EPR blends. 2. Effect of type and content of reactive groups randomly attached to SAN

in Macromolecules (2001), 34(4), 965-975

Kinetics of the poly(styrene-co-acrylonitrile)/poly(ethylene-co-propylene) (SAN/EPR) interfacial reaction has been varied by changing both the average number of reactive groups per SAN chain and the ... [more ▼]

Kinetics of the poly(styrene-co-acrylonitrile)/poly(ethylene-co-propylene) (SAN/EPR) interfacial reaction has been varied by changing both the average number of reactive groups per SAN chain and the content of reactive SAN in the SAN phase, while keeping constant the overall SAN/EPR composition, i.e., 75/25 w/w. For this purpose, reactive SAN chains containing 0.004, 0.028, 0.049, and 0.078 mol/wt % of either primary amine or carbamate (an amine precursor) have been synthesized, and the content of reactive SAN in the SAN phase has been changed from 2.5 to 73.33 wt %. It appears that the number and type of reactive groups attached onto SAN affect not only the extent of the compatibilization reaction but also the compatibilization capability of the in situ formed graft copolymer in a strong dependence on molecular weight and molecular architecture. [less ▲]