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See detailWater-soluble complexes formed by poly(2-vinylpyridinium)-block-poly(ethylene oxide) and poly(sodium methacrylate)-block-poly(ethylene oxide) copolymers
Gohy, Jean-François; Varshney, Sunil K; Jérôme, Robert ULg

in Macromolecules (2001), 34(10), 3361-3366

Formation of interpolyelectrolyte complexes (IPEC) by mixing protonated poly(2-vinylpyridine)-block-poly(ethylene oxide) (P2VP-b-PEO) with neutralized poly(methacrylic acid)-block-poly(ethylene oxide ... [more ▼]

Formation of interpolyelectrolyte complexes (IPEC) by mixing protonated poly(2-vinylpyridine)-block-poly(ethylene oxide) (P2VP-b-PEO) with neutralized poly(methacrylic acid)-block-poly(ethylene oxide) (PMAA-b-PEO) has been investigated in water. It was observed that (i) IPEC are formed in a limited pH range, which is controlled by the degree of ionization of the PMAA and P2VP blocks; (ii) IPEC self-assemble to form the core of monodisperse spherical micelles surrounded by a corona of PEO blocks; (iii) IPEC are salt-sensitive, falling apart above a critical salt concentration; (iv) IPEC are not observed at high pH, but micelles are formed by the P2VP-b-PEO copolymers, which contain an uncharged P2VP core surrounded by a PEO corona; (v) IPEC are not observed at low pH, but the PMAA-b-PEO diblocks aggregate into micelles, the core of which is formed by a hydrogen-bonded complex between PMAA and PEO; and (vi) these PMAA-b-PEO micelles, which are temperature-sensitive, show a complete reorganization of the micellar core above a critical temperature. [less ▲]

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See detailRing-opening polymerization of epsilon-caprolactone in Supercritical Carbon Dioxide
Stassin, Fabrice; Halleux, Olivier; Jérôme, Robert ULg

in Macromolecules (2001), 34(4), 775-781

The ring-opening polymerization of ε-caprolactone (CL) initiated by dibutyltin dimethoxide was studied in supercritical carbon dioxide at 40 °C, under a pressure of 210−215 bar. The polymerization is ... [more ▼]

The ring-opening polymerization of ε-caprolactone (CL) initiated by dibutyltin dimethoxide was studied in supercritical carbon dioxide at 40 °C, under a pressure of 210−215 bar. The polymerization is controlled as assessed by the linear dependence of Mn,SEC on conversion and of ln([CL]0/[CL]) on time. Moreover, there is a good agreement between Mn,SEC and Mn,calc, at least until 20 000 g/mol. The apparent rate constants of polymerization in different media increase as follows: sc CO2, CFC-113, toluene, bulk. The kinetic order in initiator for the polymerization in solution and in sc CO2 was extracted from the slope of ln kapp vs ln [Sn]0. It appears to depend on the initiator concentration in solution, which is not the case in sc CO2. [less ▲]

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See detailReactive compatibilization of SAN/EPR blends. 2. Effect of type and content of reactive groups randomly attached to SAN
Pagnoulle, Christophe; Jérôme, Robert ULg

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 ▲]

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See detailWater-soluble complexes formed by sodium poly(4-styrenesulfonate) and a poly(2-vinylpyridinium)-block-poly(ethyleneoxide) copolymer
Gohy, Jean-François; Varshney, Sunil K; Antoun, Said et al

in Macromolecules (2000), 33(25), 9298-9305

Formation of interpolyelectrolyte complexes (IPEC) between sodium poly(4-styrenesulfonate) (PSSO3Na) and a diblock copolymer consisting of a protonated poly(2-vinylpyridine) (P2VP) block and a neutral ... [more ▼]

Formation of interpolyelectrolyte complexes (IPEC) between sodium poly(4-styrenesulfonate) (PSSO3Na) and a diblock copolymer consisting of a protonated poly(2-vinylpyridine) (P2VP) block and a neutral poly(ethylene oxide) (PEO) one was investigated in water. The main experimental variables were the molecular weight (MW) of the PSSO3Na polyanion, the molar ratio of the cationic and anionic species (i.e., the stoichiometry of the complex), and the pH of the aqueous solution. It was observed that (i) the interpolyelectrolyte complexes self-assemble at least at low pH into the core of monodisperse spherical micelles surrounded by a corona of PEO blocks and possibly of uncomplexed PSSO3Na segments, (ii) their stability depends on the pH in relation to the degree of protonation of the P2VP block, whatever the MW of the PSSO3Na polyanion and the cation/anion stoichiometry, (iii) the complexes are dissociated above a critical pH and are salt-sensitive, falling apart above a critical salt concentration, and (iv) a cooperative mechanism operates, which is completely reversible. [less ▲]

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See detailNew Functional Aliphatic Polyesters by Chemical Modification of Copolymers of ε-Caprolactone with γ-(2-Bromo-2-methylpropionate)- ε-caprolactone, γ-Bromo- ε-caprolactone, and a Mixture of β-and γ-Ene- ε-caprolactone
Detrembleur, Christophe ULg; Mazza, Michaël; Lou, Xudong et al

in Macromolecules (2000), 33(17), 7751-7760

New functional aliphatic polyesters were prepared by chemical modification of brominated copolyesters. Poly(epsilon-caprolactone)-co-poly(gamma-(2-bromo-2-methylpropionate)-epsilon-caprolactone) copolymer ... [more ▼]

New functional aliphatic polyesters were prepared by chemical modification of brominated copolyesters. Poly(epsilon-caprolactone)-co-poly(gamma-(2-bromo-2-methylpropionate)-epsilon-caprolactone) copolymer was prepared and successfully converted into copolyester bearing methacrylate double bonds by dehydrohalogenation of the pendant tertiary alkyl bromides, thus leading to cross-linkable polyester. The tertiary alkyl bromide groups of the original copolyester were also quaternized by reaction with pyridine, although some side reactions occurred which Limited the reaction yield. Nevertheless, quaternization of the bromide groups of the poly(epsilon-caprolactone)-co-poly(gamma-bromo-epsilon-caprolactone) copolymer proved to be quantitative and to occur without degradation of the polyester chains. This general strategy paves the way to either amphiphilic copolyesters or water-soluble polyesters. The poly(epsilon -caprolactone)-co-poly(gamma -bromo-epsilon-caprolactone) lactone) copolymer was also quantitatively converted into unsaturated copolyester by dehydrohalogenation with formation of double bonds including acrylic-type double bonds. As an alternative, gamma-bromo-epsilon-caprolactone was first dehydrohalogenated, and the unsaturated cyclic monomer was copolymerized with epsilon-caprolactone. Finally, the nonconjugated double bonds of the copolyesters were oxidized into epoxides, except for the acrylic-type unsaturations which remained unchanged. [less ▲]

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See detailTuning of the exchange dynamics of unimers between block copolymer micelles with temperature, cosolvents, and cosurfactants
van Stam, Jan; Creutz, Serge; De Schryver, Frans C et al

in Macromolecules (2000), 33(17), 6388-6395

The dynamics of unimer exchange between aqueous micelles, formed by two amphiphilic block copolymers, i.e., poly(styrene-b-sodium methacrylate) and poly(tert-butylstyrene-b-sodium methacrylate), has been ... [more ▼]

The dynamics of unimer exchange between aqueous micelles, formed by two amphiphilic block copolymers, i.e., poly(styrene-b-sodium methacrylate) and poly(tert-butylstyrene-b-sodium methacrylate), has been investigated by steady-state fluorescence spectroscopy. The kinetics are so slow at room temperature that no exchange could be detected over several hours, while at 60 °C the exchange rate constants could be estimated. These results corroborate our previous findings that the rate is slowed down by increasing the hydrophobicity of the core. In addition to the temperature, the exchange can also be tuned by the addition of either a cosolvent or a cosurfactant. The efficiency of these additives to speed up the exchange process is related to their water solubility and their compatibility with the hydrophobic core of the micelles. The most pronounced effect on the exchange process is observed when the water solubility is low and the mixing of the additive with the hydrophobic core is favorable. [less ▲]

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See detailSmall-angle neutron scattering studies of low-polarity telechelic ionomer solutions. 3. Temperature dependence of the ionic association
Karayianni, Eleni; Jérôme, Robert ULg; Cooper, Stuart L

in Macromolecules (2000), 33(17), 6473-6484

The effect of temperature on the structure and single chain conformation of associating solutions of carboxy−telechelic polystyrene ionomers has been investigated in the dilute to semidilute concentration ... [more ▼]

The effect of temperature on the structure and single chain conformation of associating solutions of carboxy−telechelic polystyrene ionomers has been investigated in the dilute to semidilute concentration regime using the technique of small-angle neutron scattering. By applying different labeling methods, the temperature dependence of both the total scattering and single chain scattering functions was obtained independently. It was observed that temperature has a significant impact on the structure of the ionomer aggregates. Increasing temperature results in dissociation of the aggregated particles and the formation of smaller size multimers. Interestingly, the extent to which the multimers dissociate at a specific temperature compared to their initial state at room temperature is independent of concentration or ionic level, which indicates that it is independent of the degree of aggregation of particles. This leads to the conclusion that the apparent degree of aggregation can be controlled independently by concentration and temperature. For all systems studied the multimers formed through the ionic association keep an extended configuration over all the temperatures investigated. The Flory−Huggins polymer−solvent interaction parameter of the ionomer solutions showed only a slight decrease with increasing temperature. Despite the significant effect of temperature on the multimer structure, temperature was not observed to influence the single chain dimensions of the ionomer solutions. It was observed that the single chain dimensions remained unchanged over the range of variables studied. On the basis of these results, it is proposed that dissociation of the multimers takes place by disruption of the configuration of only a small number of bridging chains which connect different ionic clusters without influencing the main architecture of the associating structure. [less ▲]

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See detailReactive compatibilization of SAN/EPR blends. 1. Dependence of the phase morphology development on the reaction kinetics
Pagnoulle, Christophe; Koning, Cor; Leemans, Luc et al

in Macromolecules (2000), 33(17), 6275-6283

SAN containing 20 wt % of reactive SAN-X has been melt blended with EPDM containing 50 wt % of EP chains grafted by maleic anhydride (EP-g-MA). Two types of reactive groups (X) have been attached to SAN ... [more ▼]

SAN containing 20 wt % of reactive SAN-X has been melt blended with EPDM containing 50 wt % of EP chains grafted by maleic anhydride (EP-g-MA). Two types of reactive groups (X) have been attached to SAN (2 mol % of X), i.e., a primary amine and a precursor of it at the processing temperature, i.e., a carbamate. The SAN/rubber weight composition was kept constant at 75/25. The development of the phase morphology from pellet-sized rubber particles to dispersed submicrometer droplets has been investigated during reactive mixing for the two types of reactive SAN and has been found to depend on the interpolymer reaction rate and thus on the relative reactivity of the amine and the carbamate groups attached to SAN toward the maleic anhydride function of EP. [less ▲]

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See detailAggregates formed by amphoteric diblock copolymers in water
Gohy, Jean-François; Creutz, Serge; Garcia, Myriam et al

in Macromolecules (2000), 33(17), 6378-6387

The associating behavior of a series of monodisperse poly(2-(dimethylamino)ethyl methacrylate)-b-poly(methacrylic acid) (PDMAEMA-b-PMAA) ampholytic diblock copolymers has been studied in water in the ... [more ▼]

The associating behavior of a series of monodisperse poly(2-(dimethylamino)ethyl methacrylate)-b-poly(methacrylic acid) (PDMAEMA-b-PMAA) ampholytic diblock copolymers has been studied in water in the dilute regime as a function of pH and salt concentration. Dynamic light scattering (DLS) has been used to monitor the association behavior and transmission electron microscopy (TEM) to visualize the morphology of the aggregates. At and around the isoelectric point (IEP) of the ampholytic diblocks, strong electrostatic interactions occur and lead to the formation of insoluble complexes between negatively and positively charged blocks. These electrostatic interactions can be screened by the addition of salt, which leads to the partial dissolution of the material, according to Debye screening. For samples containing a major PDMAEMA block, spherical micelles are observed below the IEP. These micelles consist of a PMAA core surrounded by a water-soluble protonated PDMAEMA corona. At and above the IEP, these samples are insoluble. Spherical micelles are also formed below the IEP for samples containing a minor PDMAEMA block. These copolymers are insoluble at and around the IEP, whereas solubility is observed above the IEP with formation of aggregates of remarkable morphologies, including hollow spheres and complex compartmentalized aggregates. This aggregation is most favorable at high pH, and it cannot be accounted for only by electrostatic interaction between oppositely charged blocks. Indeed, short-range hydrophobic interaction between uncharged PDMAEMA blocks seems to play a key role in the association process. This is emphasized by quaternized poly(2-(dimethylamino)ethyl methacrylate)-b-poly(methacrylic acid) ampholytic copolymers which are carrying a permanent positive charge on the aminated monomeric units and do not form these particular aggregates. [less ▲]

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See detailAdsorption kinetics of a hydrophobic-hydrophilic diblock polyelectrolyte at the solid- aqueous solution interface: a slow birth and fast growth process
Abraham, T.; Giasson, S.; Gohy, Jean-François et al

in Macromolecules (2000), 33(16), 6051-6059

The adsorption kinetics of a diblock copolymer poly(tert-butyl methacrylate)-b-poly(glycidyl methacrylate sodium sulfonate) on hydrophobic substrate from aqueous solution under different added monovalent ... [more ▼]

The adsorption kinetics of a diblock copolymer poly(tert-butyl methacrylate)-b-poly(glycidyl methacrylate sodium sulfonate) on hydrophobic substrate from aqueous solution under different added monovalent salt (NaCl) concentrations was investigated using an ellipsometric technique. The effect of monovalent counterion size on adsorption kinetics of the same copolymer on hydrophobic surfaces was also part of the investigation. The results, in general, indicate that the adsorption process on solid surfaces occurs through the anchoring of hydrophobic chains due to the short-ranged hydrophobic interactions. The kinetic data reveal three distinct stages in the adsorption process: an incubation period, a subsequent fast growth process of the polymer layer, and a plateau (equilibrium) region. These three stages are found to be influenced by salt concentration as well as counterion size. The equilibrium adsorption density increases as a function of salt concentration, and the dependence is found to be different from the theoretical predictions. The incubation time increases with salt concentration according to a power law dependence, and a simple bound ionic layer formation on the substrate is proposed as a possible explanation for this observation. An attempt has been made to explain the growth process in terms of an Avrami type ordering process. The Avrami analysis indicates that the buildup of polyelectrolyte layer structure depends on added salt conditions. Our kinetic data suggest that the diffusion of the chains to the surface is not the rate-controlling process for adsorption. A slow birth (nucleation) and fast growth of the layer seem to be the determining adsorption process. [less ▲]

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See detailDeformation behavior of weakly segregated block copolymers. 2. Correlation between phase behavior and deformation mechanisms of diblock copolymers
Weidisch, R.; Schreyeck, G.; Ensslen, M. et al

in Macromolecules (2000), 33(15), 5495-5504

The deformation behavior of poly(styrene-b-butyl methacrylate) diblock copolymers, PS-b-PBMA, is studied by high-voltage electron microscopy (HVEM) with an in-situ tensile device. While in the first part ... [more ▼]

The deformation behavior of poly(styrene-b-butyl methacrylate) diblock copolymers, PS-b-PBMA, is studied by high-voltage electron microscopy (HVEM) with an in-situ tensile device. While in the first part the phase behavior of PS-b-PBMA diblock copolymers is investigated via small-angle neutron scattering (SANS), in the second part the deformation behavior depending on composition and molecular weight is discussed. Disordered block copolymers have the same deformation mechanism as the corresponding homopolymers, while microphase-separated block copolymers undergo a cavitation mechanism. At the order−disorder transition, ODT, a transition from crazing to cavitation mechanism is found via HVEM. Moreover, a sharp increase of the diameter of craze fibrils occurs at the ODT, demonstrating that the craze microstructure is strongly influenced by phase behavior. As the incompatibility increases with increasing molecular weight, deformation mechanisms such as diversion and termination of crazes are observed for intermediately segregated block copolymers. The discussed correlation between phase behavior and deformation mechanisms indicates the existence of a unified scheme for deformation behavior of diblock copolymers depending on the strength of segregation, χN. [less ▲]

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See detailPolymer dynamics In an Interface-confined space: NMR study of poly(hexyl ethacrylate)-block-poly(acrylic acid) and poly(dodercyl methacrylate)-block-poly(acrylic acid) micelles in D2O
Kritz, J.; Brus, J.; Plestil, J. et al

in Macromolecules (2000), 33(11), 4108-4115

The mobility of distant methyl side groups in poly(hexyl methacrylate)-block-poly(sodium acrylate) (PHMA−PAANa) and poly(dodecyl methacrylate))-block-poly(sodium acrylate) (PLMA−PAANa) micelles, dispersed ... [more ▼]

The mobility of distant methyl side groups in poly(hexyl methacrylate)-block-poly(sodium acrylate) (PHMA−PAANa) and poly(dodecyl methacrylate))-block-poly(sodium acrylate) (PLMA−PAANa) micelles, dispersed in D2O and characterized by SANS, was studied using 1H single and double quantum high-resolution and MAS NMR. Transverse and rotating-frame relaxation was studied at temperatures 320−345 K in the original micellar solutions and in the systems with their viscosity gradually increased by additions of high-molecular-weight poly(ethylene oxide) and with the micellar cores gradually swollen by chlorobenzene. The relaxation data were quantitatively evaluated using a pragmatic model based on Cohen-Addad's theory. The results obtained strongly indicate that the side groups are relatively immobilized to an even higher degree than in poly(2-ethylhexyl acrylate)-block-poly(acrylic acid) micelles at the same conditions. The most immobilized groups are at or near the interface. Possible underlying effects, including penetration resistance of the surrounding water molecules, fixation of the polymer backbone at the interface, and motional correlation between the distant side group and the backbone are discussed. [less ▲]

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See detailControlled ring-opening polymerization of epsilon-caprolactone promoted by "in situ" formed yttrium alkoxides
Martin, Eric; Dubois, Philippe ULg; Jérôme, Robert ULg

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 ▲]

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See detailElongation of telechelic ionomers under shear: a rheological and rheo-optical study
Chassenieux, Christophe; Tassin, Jean-François; Gohy, Jean-François et al

in Macromolecules (2000), 33(5), 1796-1800

The behavior under shear of solutions of α,ω-lithium sulfonato polystyrene (α,ω-LiPSS100) in toluene has been investigated by rheo-optics and rheology. Shear-thickening is observed and related to a strong ... [more ▼]

The behavior under shear of solutions of α,ω-lithium sulfonato polystyrene (α,ω-LiPSS100) in toluene has been investigated by rheo-optics and rheology. Shear-thickening is observed and related to a strong increase of birefringence and a pronounced and rapid alignment of the polymer chains toward the flow direction leading to an important elasticity of the fluids. The draw ratio of the polymer chains under shear has been estimated from the rheo-optical data. When the fraction of loops is taken into account, draw ratios on the order of 4 are calculated in the shear thickening regime. [less ▲]

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See detailSynthesis, morphology, and mechanical properties of poly(methyl methacrylate)-b-poly(n-butyl acrylate)-b-poly (methyl methacrylate) triblocks. Ligated anionic polymerization vs atom transfer radical polymerization
Tong, Jiang-Dong; Moineau, Georges; Leclère, Philippe et al

in Macromolecules (2000), 33(2), 470-479

Poly(methyl methacrylate)-b-poly(n-butyl acrylate)-b-poly(methyl methacrylate) triblock copolymers have been prepared by ligated anionic polymerization (LAP; 8K-50K-8K) and atom transfer radical ... [more ▼]

Poly(methyl methacrylate)-b-poly(n-butyl acrylate)-b-poly(methyl methacrylate) triblock copolymers have been prepared by ligated anionic polymerization (LAP; 8K-50K-8K) and atom transfer radical polymerization (ATRP; 9K-51K-9K). Size exclusion chromatography, nuclear magnetic resonance, and differential scanning calorimetry have confirmed that the molecular structure of the two triblock copolymers is essentially identical. However, important differences are found in dynamic mechanical properties, viscoelastic properties, and stress−strain behavior. Indeed, the ATRP copolymer has low storage modulus, high complex viscosity, high order−disorder transition temperature, and poor ultimate tensile strength and elongation at break, compared to those of the LAP analogue. Marked differences also observed by tapping mode atomic force microscopy in the microscopic morphology of thin films of these copolymers. All these observations can be explained by the slow initiation of MMA by the poly(n-butyl acrylate) macroinitiator used in ATRP in contrast to what happens when MMA is added to living poly(tert-butyl acrylate) anions. As a result, the polydispersity of the short poly(methyl methacrylate) (PMMA) outer blocks is much broader in the ATRP copolymer, although the polydispersity index of the triblock is only 1.15. This heterogeneous structure of the ATRP triblock is also supported by the comparison of homo-PMMAs prepared by LAP and ATRP. [less ▲]

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See detailRing-Opening Polymerization of γ-bromo-ε-caprolactone : A novel route to functionalized aliphatic polyesters
Detrembleur, Christophe ULg; Mazza, Michaël; Halleux, Olivier et al

in Macromolecules (2000), 33(1), 14-18

The synthesis, characterization, and polymerization of a new cyclic ester, gamma-bromo-epsilon-caprolactone (gamma-BrCL), are reported. The ring-opening polymerization (ROP) of this new monomer initiated ... [more ▼]

The synthesis, characterization, and polymerization of a new cyclic ester, gamma-bromo-epsilon-caprolactone (gamma-BrCL), are reported. The ring-opening polymerization (ROP) of this new monomer initiated from Al((OPr)-Pr-i)(3) as initiator in toluene at 0 degrees C was found to be living and proceeds by a coordination-insertion mechanism. Random and block copolymerizations of this gamma-BrCL with epsilon-caprolactone (epsilon-CL) were also found to be living as evidenced by the experimental molecular weight which is consistent with that expected from the monomer to initiator molar ratio, the narrow polydispersity, and the good agreement between the comonomers molar fraction in the comonomer feed and the copolymer. The thermal transitions (Tg and Tm) in the epsilon-CL/gamma-Br-CL random copolymers depend strongly on the gamma-BrCL content. Increasing the gamma BrCL content in the copolymer [F(BrCL)] increased the Tg of the copolymer from -61 degrees C for poly(epsilon-caprolactone) to -16.5 degrees C for the poly( gamma-BrCL) homopolymer but decreased the Tm of the PCL to contents of similar to 30 mol % of gamma BrCL [F(BrCL) =0.3]Beyond this value, the copolymers were found to be amorphous and exist as viscous liquids. [less ▲]

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See detailSynthesis and characterization of poly(methyl methacrylate)-block-poly(n-butyl acrylate)-block-poly(methyl methacrylate) copolymers by two-step controlled radical polymerization (ATRP) catalyzed by NiBr2(PPh3)2, 1+
Moineau, Georges; Minet, Michaël; Teyssié, Philippe et al

in Macromolecules (1999), 32(25), 8277-8282

Poly(methyl methacrylate)-block-poly(n-butyl acrylate)-block-poly(methyl methacrylate) triblock copolymers (MnBM) have been synthesized by the sequential controlled radical polymerization (atom transfer ... [more ▼]

Poly(methyl methacrylate)-block-poly(n-butyl acrylate)-block-poly(methyl methacrylate) triblock copolymers (MnBM) have been synthesized by the sequential controlled radical polymerization (atom transfer radical polymerization, ATRP) of n-butyl acrylate (n-BuA) followed by methyl methacrylate (MMA). The polymerization of n-BuA has been first initiated by the difunctional (diethyl meso-2,5-dibromoadipate) initiator in the presence of the NiBr2(PPh3)2 catalyst. After isolation, the α,ω-dibromo poly(n-butyl acrylate) chains have been used as macroinitiators for the polymerization of either n-BuA or MMA leading to chain extension or to the desired triblock copolymers, respectively. The kinetic study of the two-step process has shown that the initiation of the MMA polymerization by the poly(n-BuA) macroinitiator is slow and leads to PMMA outer blocks of broad polydispersity. Differential scanning calorimetry (DSC) and dynamical mechanical analysis (DMA) have confirmed the two-phase morphology of the triblocks. Finally, DMA and tensile testing of these copolymers have emphasized poor mechanical properties in possible relation to the broad polydispersity of the PMMA outer blocks. [less ▲]

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See detailStudy of the propagation center in the anionic polymerization of (meth)acrylic monomers: NMR study of Di-tert-butyl 2-Lithio-2.4'-trimethylglutarate and living poly(tert-butyl methacrylate) oligomers in THF/toluene mixtures
Zune, Catherine; Dubois, Philippe ULg; Grandjean, Jean ULg et al

in Macromolecules (1999), 32(7), 5477-5486

Solvation influences both the stereoregularity and molecular weight distribution (MWD) of poly(tert-butyl methacrylate) (PtBMA) prepared by anionic polymerization of tBMA with a lithium counterion in THF ... [more ▼]

Solvation influences both the stereoregularity and molecular weight distribution (MWD) of poly(tert-butyl methacrylate) (PtBMA) prepared by anionic polymerization of tBMA with a lithium counterion in THF/toluene mixed solvents at −78 °C. As a probe of the structural changes of the propagating species, multinuclear 7Li, 1H, and 13C NMR analysis of di-tert-butyl 2-lithio-2,4,4‘-trimethylglutarate (a model dimer, A) and of short-length living PtBMA chains is reported and discussed. Whatever the system, the main structure of the lithium ester enolate in THF/toluene mixtures is similar to that one reported in THF. In the case of A and for toluene contents exceeding 50% v/v, partly organized pseudophases can additionally be detected in the 7Li NMR spectra, but they do not provide well-developed 1H and 13C NMR signals. The chemical shifts of 1H and 13C signals of A support the dimeric form of this model. An equilibrium between dimeric and nonaggregated living PtBMA chains has been previously proposed to dominate in pure THF. However, marked self-termination of low-molecular weight living oligomers prepared in THF/toluene mixtures can be observed at 263 K, in contrast to the stability observed in pure THF up to 298 K. Another contrasting feature is the broadening of the molecular weight distribution which can be explained by an aggregation process that stabilizes oligomers at the early stage of the anionic polymerization as supported by SEC-RI and SEC-UV eluograms. [less ▲]

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