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See detailSelf-aggregation of poly(methyl methacrylate)-block-poly(sulfonated glycidyl methacrylate) copolymers
Gohy, Jean-François; Antoun, Sayed; Jérôme, Robert ULg

in Polymer (2001), 42(21), 8637-8645

The self-aggregation of a series of amphiphilic poly(methyl methacrylate)-block-poly(sulfonated glycidyl methacrylate) (PMMA-b-PSGMA) copolymers in water has been studied by dynamic light scattering (DLS ... [more ▼]

The self-aggregation of a series of amphiphilic poly(methyl methacrylate)-block-poly(sulfonated glycidyl methacrylate) (PMMA-b-PSGMA) copolymers in water has been studied by dynamic light scattering (DLS), size exclusion chromatography (SEC) and surface tension measurements. All the copolymers considered in this study form micelles which, however, aggregate into larger structures as shown by DLS and SEC. These larger structures dissociate into smaller ones upon increasing the temperature. The extent of this dissociation process is strongly dependent on the copolymer composition. It is large as the content of the hydrophilic block is high. [less ▲]

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See detailMetallocene catalyzed polymerization of ethylene in the presence of graphite. 2. Structure and electrical properties of the composites
Pluta, Miroslaw; Alexandre, Michaël ULg; Blacher, Silvia ULg et al

in Polymer (2001), 42(22), 9293-9300

Structure and electrical properties of conducting polyethylene/graphite composites have been studied in relation to the preparation method, i.e. (i) the polymerization-filling technique (PFT), in which ... [more ▼]

Structure and electrical properties of conducting polyethylene/graphite composites have been studied in relation to the preparation method, i.e. (i) the polymerization-filling technique (PFT), in which the polyolefinic chains are growing from the graphite surface, (ii) the slurry polymerization of ethylene in the presence of untreated graphite, and (iii) the mechanical blending of preformed polyethylene and graphite. The extent of the filler dispersion depends on the method used for the composite preparation. Moreover, the graphite particles can be oriented by the molding of the samples used for the measurement of the electrical properties. This orientation is as pronounced as the melt viscosity of polyethylene is low, this characteristic feature changing with the preparation method. These structural details have consequences on the electrophysical properties and the percolation threshold. Finally, the thermal dependence of the electrical resistivity has been studied. [less ▲]

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See detailMicellization of quaternized poly(2-(dimethylamino)ethyl methacrylate)-block-poly(methyl methacrylate) copolymers in water
Antoun, Sayed; Gohy, Jean-François; Jérôme, Robert ULg

in Polymer (2001), 42(8), 3641-3648

Micellization of a series of amphiphilic quaternized poly(2-(dimethylamino)ethyl methacrylate)-block-poly(methyl methacrylate) (PQDMAEMA-b-PMMA) copolymers has been studied in water. The alkyl halide used ... [more ▼]

Micellization of a series of amphiphilic quaternized poly(2-(dimethylamino)ethyl methacrylate)-block-poly(methyl methacrylate) (PQDMAEMA-b-PMMA) copolymers has been studied in water. The alkyl halide used for the quaternization of the aminated block has an effect on the solution properties of the diblocks, that have been investigated by dynamic light scattering and surface tension measurements. When a short length alkyl halide is used, the diblock copolymers behave like traditional amphiphiles, whereas their behavior is similar to polysoaps in case of long alkyl halides. The size of the micelles increases when 1-bromopropan-3-ol is substituted for 1-bromopropane in the quaternization reaction. It is, however, independent of the structure of butyl bromide, i.e. n-butyl vs tert-butyl bromide. The solution properties of a star-shaped PQDMAEMA-b-PMMA copolymer have also been studied and compared to the linear counterpart. The star-shaped architecture actually prevents the block copolymer to be properly oriented at the air/water interface in agreement with the formation of unimer micelles. [less ▲]

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See detailMorphology and mechanical properties of poly(methylmethacrylate)-b-poly(alkylacrylate)-b-poly(methylmethacrylate)
Tong, J. D.; Leclère, Philippe; Doneux, C. et al

in Polymer (2001), 42(8), 3503-3514

A series of well-defined poly(methylmethacrylate) (PMMA)-b-poly(alkylacrylate)-b-PMMA triblock copolymers (MAM) has been synthesized by transalcoholysis of PMMA-b-poly(tert-butylacrylate)-b-PMMA ... [more ▼]

A series of well-defined poly(methylmethacrylate) (PMMA)-b-poly(alkylacrylate)-b-PMMA triblock copolymers (MAM) has been synthesized by transalcoholysis of PMMA-b-poly(tert-butylacrylate)-b-PMMA precursors by alkyl alcohols. The molecular weight (MW) of the outer PMMA blocks is in the 10,000-50,000 range, compared to 50,000-200,000 for the inner poly(alkylacrylate) block. Phase separation, as studied in direct space by atomic force microscopy, is observed for all the investigated triblock copolymers, except for the PMMA-b-poly(ethylacrylate)-b-PMMA and the PMMA-b-poly(n-propylacrylate)-b-PMMA triblocks of 10,000-50,000-10,000 MW. The ultimate tensile strength measured for the MAM triblocks is strongly dependent on the MW between chain entanglements for the central block. The tensile behavior is however affected by the partial miscibility of the outer and inner blocks when the PMMA MW is low. When this situation prevails, it makes the melt processing possible at temperatures lower than 200°C. [less ▲]

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See detailParticle-in-particle morphology for the dispersed phase formed in reactive compatibilization of SAN/EPDM blends
Pagnoulle, Christophe; Jérôme, Robert ULg

in Polymer (2001), 42(5), 1893-1906

Poly(ethylene-co-propylene-co-diene) (EPDM) containing 50 wt% of poly(ethylene-co-propylene) grafted with maleic anhydride (EP-g-MA) has been melt blended with poly(styrene-co-acrylonitrile) (SAN) added ... [more ▼]

Poly(ethylene-co-propylene-co-diene) (EPDM) containing 50 wt% of poly(ethylene-co-propylene) grafted with maleic anhydride (EP-g-MA) has been melt blended with poly(styrene-co-acrylonitrile) (SAN) added with various amounts of reactive SAN, i.e. SAN bearing either primary amine (SAN-NH2) or carbamate groups (SAN-carb). Carbamate groups are precursors of primary amines by thermal thermolysis during melt processing. These reactive systems are good models for studying the effect of the kinetics of the interfacial reaction on the phase morphology. Reaction of maleic anhydride with the primary amine is indeed very fast, at high temperature, in contrast to the reaction with carbamate, which is controlled by the carbamate thermolyis into primary amine. Special attention has been paid to the experimental conditions required for the development of the particle-in-particle morphology for the dispersed phase. Depending on the mixing sequence and the grafting kinetics (NH2/MA versus carb/MA), this particular phase morphology can be forced or occurs spontaneously. [less ▲]

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See detailPremade versus in situ formed compatibilizer at the PS/PMMA interface: contribution of the Raman confocal microscopy to the fracture analysis
Koulic, Christian; Yin, Zhihui; Pagnoulle, Christophe et al

in Polymer (2001), 42(7), 2947-2957

The interface of a two-layer assembly of polystyrene (PS) and poly(methyl methacrylate) (PMMA) was modified by an intermediate layer of either a premade poly(styrene-g-methyl methacrylate) copolymer (P(S ... [more ▼]

The interface of a two-layer assembly of polystyrene (PS) and poly(methyl methacrylate) (PMMA) was modified by an intermediate layer of either a premade poly(styrene-g-methyl methacrylate) copolymer (P(S-g-MMA)) or a preblend of mutually reactive PS and PMMA synthesized by atom transfer radical polymerization (ATRP). No significant difference was found in the interfacial fracture toughness measured by the double cantilever beam test, although the morphology of the interfacial region was not the same when observed by transmission electron microscopy. The premade copolymer formed a distinct interphase, in contrast to the sharp interface that was observed in the case of the reactive system. The analysis of the fracture surfaces by Raman confocal microscopy showed that the fracture occurred alternatively in the PS phase and either at the PS/copolymer interface for the non reactive system or at the PS/PMMA interface for the reactive one. [less ▲]

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See detailDetermination of the stability constants of uranyl/polymer complexes by differential pulse polarography
Leroy, D.; Martinot, Lucien; Jérôme, Christine ULg et al

in Polymer (2001), 42(10), 4589-4596

Differential pulse polarography (DPP) allows for the determination of the stability constants (K) and the stoichiometry (n) for the complexation of the UO22+ ion by various monomers and the parent ... [more ▼]

Differential pulse polarography (DPP) allows for the determination of the stability constants (K) and the stoichiometry (n) for the complexation of the UO22+ ion by various monomers and the parent polymers. The experimental observation is the shift of the totally reversible reduction wave UO22++e- UO2+ toward more cathodic potentials when the complexing monomer or polymer is added to an uranyl nitrate aqueous solution. This shift is, however, much greater when the polymer is used rather than the monomer, in line with a higher stability of the complexes (Kpolymer>>Kmonomer). A theoretical stability scale of the polymers/UO22+ complexes was compared to an experimental one based on dynamic leaching tests. [less ▲]

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See detailTernary polymer blend with core-shell dispersed phases: effect of the core-forming polymer on phase morphology and mechanical properties
Luzinov, Igor; Pagnoulle, Christophe; Jérôme, Robert ULg

in Polymer (2000), 41(19), 7099-7109

Phase morphology and mechanical properties of ternary blends consisting of PS (polystyrene), SBR (styrene butadiene rubber) and different polyolefins (POs) have been studied. PS, systematically forms the ... [more ▼]

Phase morphology and mechanical properties of ternary blends consisting of PS (polystyrene), SBR (styrene butadiene rubber) and different polyolefins (POs) have been studied. PS, systematically forms the matrix, SBR and PO being combined in the dispersed phase. Although POs of various melt viscosity and stiffness are used, the binary (SBR/PO) dispersed phase is of a core-shell structure, in which PO forms the core. Upon increasing the viscosity of PO, the average size of the cores and the SBR domains including them increases. Comparison of the experimental shear storage modulus of the blends with theoretical predictions indicates that the stress transfer from the PS matrix to the PO core through the SBR shell depends on the modulus of the SBR envelope. The ultimate mechanical properties of the ternary blends are sensitive to the stiffness of the PO core. [less ▲]

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See detailReactive compatibilization of PC/PVDF polymer blends by zinc carboxylate containing poly(methylmethacrylate)ionomers
Moussaif, Noureddine; Pagnoulle, Christophe; Jérôme, Robert ULg

in Polymer (2000), 41(15), 5551-5562

Polycarbonate (PC) has been reacted with a random copolymer of methylmethacrylate and 6 mol% of acrylic acid (poly(MMA-co-AA)) and with this copolymer neutralized (totally or not) by Zn cations. When ... [more ▼]

Polycarbonate (PC) has been reacted with a random copolymer of methylmethacrylate and 6 mol% of acrylic acid (poly(MMA-co-AA)) and with this copolymer neutralized (totally or not) by Zn cations. When conducted in solution at 240°C, the reaction leads to the grafting of PC onto the copolymer neutralized or not. In the melt at 235°C, the grafting reaction occurs only when the copolymer is at least partly neutralized. Whatever the experimental conditions (solution or bulk), PMMA does not react with PC, which confirms that the acidolysis of PC is at the origin of the grafting reaction. Poly(vinylidene fluoride) (PVDF) and PC have been melt blended at 235°C in the presence of the poly(MMA-co-AA) copolymer totally neutralized or not by Zn cations, the purpose being the reactive formation of PMMA-g-PC copolymer that would act as compatibilizer for the PC/PVDF blend. The phase morphology and the mechanical properties of the compatibilized PC/PVDF blends have been compared with the parent non-reactive polyblends. Compared to the modification of PVDF by 20 wt% of PMMA, the use of 20 wt% of the partly neutralized poly(MMA-co-AA) copolymer decreases further the average size of the dispersed phase, enhances its adhesion to the matrix, and results in a considerable increase of the elongation at break. The beneficial effect of zinc carboxylate in the PMMA copolymer is explained by the grafting of PC onto PMMA at the interface. [less ▲]

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See detailAnionic synthesis of cyclic anhydride end-capped poly(methyl methacrylate)
Fallais, Isabelle; Pantoustier, Nadège; Devaux, Jacques et al

in Polymer (2000), 41(14), 5535-5539

This paper reports on the anionic synthesis of poly(methyl methacrylate) chains end-capped by cyclic anhydride. The method is based on the chemical derivatization of a precursor tert-butyl diester end ... [more ▼]

This paper reports on the anionic synthesis of poly(methyl methacrylate) chains end-capped by cyclic anhydride. The method is based on the chemical derivatization of a precursor tert-butyl diester end-group. Compared to the thermal modification, which was previously used, this method allows intermolecular coupling and polymer degradation to be avoided. But up to now, the final anhydride content remains moderate and has still to be improved. [less ▲]

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See detailSynthesis and bulk properties of poly(methyl methacrylate)-b-poly(isooctyl acrylate(isooctyl acrylate)-b-poly(methyl methacrylate)
Tong, J. D.; Leclère, Philippe; Doneux, C. et al

in Polymer (2000), 41(12), 4617-4624

A series of well-defined poly(methylmethacrylate) (PMMA)-b-poly(isooctylacrylate) (PIOA)-b-PMMA triblock copolymers (MIM) has been synthesized by transalcoholysis of PMMA-b-poly(tert-butylacrylate) (PtBA ... [more ▼]

A series of well-defined poly(methylmethacrylate) (PMMA)-b-poly(isooctylacrylate) (PIOA)-b-PMMA triblock copolymers (MIM) has been synthesized by transalcoholysis of PMMA-b-poly(tert-butylacrylate) (PtBA)-b-PMMA precursors (MTM) by isooctyl alcohol. Phase separation is observed for all the investigated triblock copolymers, thus containing PMMA outer blocks in the 3500-50,000 molecular weight (MW) range and PIOA inner block with MW in the 100,000-300,000 range. The ultimate tensile properties of these MIM triblock copolymers are poor even when PMMA blocks of 50,000 MW are associated with an inner PIOA block of 300,000 MW. A reasonable explanation should be found in the molecular weight between chain entanglements (Me), which has been estimated at 60,000 for PIOA, much higher than Me for the traditional polydiene central blocks in the well-known thermoplastic elastomers of the triblock type. The tensile behavior of MIM copolymers has been successfully accounted for by a simple elastomer model free from chain entanglements, supporting the view that the lack of entanglements in the central block is very detrimental to the mechanical properties of the investigated fully (meth)acrylate triblock copolymers. [less ▲]

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See detailDependence of phase morphology and mechanical properties of PS/SBR/PE ternary blends on composition: transition from core-shell to triple-phase continuity structures
Luzinov, Igor; Pagnoulle, Christophe; Jérôme, Robert ULg

in Polymer (2000), 41(9), 3381-3389

The weight ratio of PE and PS in ternary PS/SBR/PE blends has been changed at constant SBR content (25 wt%). When the matrix is either PE or PS, the dispersed phase has a core-shell structure with SBR ... [more ▼]

The weight ratio of PE and PS in ternary PS/SBR/PE blends has been changed at constant SBR content (25 wt%). When the matrix is either PE or PS, the dispersed phase has a core-shell structure with SBR forming the shell. The size of the core expectedly increases with the content of the core-forming polymer. In some composition range, the three phases are simultaneously continuous, SBR being localized in between the co-continuous PE and PS phases. The ultimate mechanical properties of the ternary blends containing SBR/PE and SBR/PS core-shell dispersed phases are close to the properties of the PS/SBR and PE/SBR binary blends, respectively. Some synergism in the elongation at break of the ternary blends is observed when core-shell SBR/PS phases are dispersed in PE matrix. [less ▲]

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See detailSingle-step reactive extrusion of PLLA in a corotating twin-screw extruder promoted by 2-ethylhexanoic acid tin(II) salt and triphenylphosphine
Jacobsen, S.; Fritz, H. G.; Degée, Philippe et al

in Polymer (2000), 41(9), 3395-3403

The ring opening polymerisation of L,L-lactide using an equimolar complex of 2-ethylhexanoic acid tin(II) salt Sn(Oct)2 and triphenylphosphine P( )3 as catalyst shows for the first time a reactivity ... [more ▼]

The ring opening polymerisation of L,L-lactide using an equimolar complex of 2-ethylhexanoic acid tin(II) salt Sn(Oct)2 and triphenylphosphine P( )3 as catalyst shows for the first time a reactivity providing a polymerisation propagation rate fast enough to imagine a continuous single-step reactive extrusion process for bulk polymerisation. The ring opening polymerisation has been realised on a corotating closely intermeshing twin-screw extruder, using a specially designed screw concept to provide sufficient energy input and mixing for further enhancement of the propagation rate, without detrimentally enhancing depolymerisation or transesterification reactions. Using one chosen screw and processing concept on a twin-screw extruder with 25 mm diameter and a L/D-ratio of 48, the influence of different processing parameters on the resulting molecular parameters of the Polylactide (PLA) has been determined. Furthermore, the mechanical property profile of the generated PLA-polymers is discussed and related to the molecular parameters. [less ▲]

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See detailXPS analysis of the PC/PVDF interface modified by PMMA. Location of the PMMA at the interface
Moussaif, Noureddine; Pagnoulle, Christophe; Riga, Joseph et al

in Polymer (2000), 41(9), 3391-3394

Polycarbonate (PC) and polyvinylidenefluoride (PVDF) are two immiscible polymers, which form two-phase polyblends with a weak interfacial adhesion and a high interfacial tension. This situation may be ... [more ▼]

Polycarbonate (PC) and polyvinylidenefluoride (PVDF) are two immiscible polymers, which form two-phase polyblends with a weak interfacial adhesion and a high interfacial tension. This situation may be changed by the addition of polymethylmethacrylate (PMMA), which is miscible with PVDF and concentrates at the PVDF/PC interface. Location of PMMA at the PC/PVDF interface has been confirmed by XPS analysis, which shows that the interface enrichment in PMMA already takes place when only 10 wt% PMMA is premixed with PVDF. [less ▲]

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See detailSynthesis of poly(methyl methacrylate)-b-poly(n-butyl acrylate)-b-poly(methyl methacrylate) triblocks and their potential as thermoplastic elastomers
Tong, J. D.; Jérôme, Robert ULg

in Polymer (2000), 41(7), 2499-2510

A series of well defined poly(methyl methacrylate) (PMMA)-b-poly(n-butyl acrylate) (PnBA)-b-PMMA triblock copolymers (MnBM) has been synthesized by transalcoholysis of PMMA-b-poly(tert-butylacrylate ... [more ▼]

A series of well defined poly(methyl methacrylate) (PMMA)-b-poly(n-butyl acrylate) (PnBA)-b-PMMA triblock copolymers (MnBM) has been synthesized by transalcoholysis of PMMA-b-poly(tert-butylacrylate) (PtBA)-b-PMMA precursors (MTM) by n-butanol. Phase separation is observed for all the investigated triblock copolymers, which contain PMMA outer blocks in the 5000-50 000 molecular weight (MW) range and PnBA inner blocks with MW in the 100 000-200 000 range. Although the ultimate tensile properties of these MnBM triblock copolymers are poor compared to traditional diene-based TPEs (SBS and SIS), they are much better than those ones reported for PMMA-b-poly(isooctyl acrylate) (PIOA)-b-PMMA triblocks (MIM). A reasonable explanation for this observation is found in the average molecular weight between chain entanglements (Me) that has been estimated to be 28 000 for the central PnBA rubbery block, which is consistently much smaller than for PIOA (59 000) and substantially higher than Me for polybutadiene (1700) and polyisoprene (6100). The tensile behavior of MnBM copolymers cannot be fitted by either a simple elastomer model free from chain entanglements (suitable to MIM) or by a "filler" modified rubber model (suitable for diene-based TPEs), supporting the hypothesis that the mechanical properties of the investigated (meth)acrylate thermoplastic elastomers are significantly affected by any change in Me of the central acrylate block. Viscoelastic analysis shows that MnBM triblocks are of higher complex viscosity than the SBS and SIS analogs, leading to a shift in the order-disorder transition temperature to much higher temperature, unless the outer PMMA blocks are of very low molecular weight (5000). [less ▲]

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See detailMiscibility of poly(vinylidene fluoride) and poly(methylmethacrylate-co-zinc polyacrylate) ionomers
Moussaif, Noureddin; Jérôme, Robert ULg

in Polymer (1999), 40(24), 6831-6839

A random copolymer of methyl methacrylate and 5.7 mol.% of acrylic acid has been neutralized by zinc cation to different extents in order to study the effect of zinc carboxylate pendant groups on the ... [more ▼]

A random copolymer of methyl methacrylate and 5.7 mol.% of acrylic acid has been neutralized by zinc cation to different extents in order to study the effect of zinc carboxylate pendant groups on the miscibility of poly(methyl methacrylate) (PMMA) and poly(vinylidene fluoride) (PVDF). The interaction parameter (χ) has been calculated from the experimental depression of the PVDF melting point. χ is minimum at zinc carboxylate content of 2.8 mol.%. The dynamic mechanical analysis of the PVDF-PMMA ionomer binary blends does not agree with the additivity rule of the properties, consistently with the phase morphology that changes with composition. Blends are indeed amorphous as long as the PVDF content does not exceed 40 wt.%, otherwise, semicrystalline PVDF coexists with an amorphous mixed PVDF/copolymer phase. [less ▲]

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See detailCompatibilization of immiscible polymer blends (PV/PVDF) by the addition of a third polymer (PMMA): analysis of phase morphology and mechanical properties
Moussaif, Noureddin; Jérôme, Robert ULg

in Polymer (1999), 40(14), 3919-3932

Compatibilization of the immiscible polycarbonate (PC)/polyvinylidenefluoride (PVDF) pair by a third homopolymer, i.e. polymethylmethacrylate (PMMA), was studied in relation to phase morphology and ... [more ▼]

Compatibilization of the immiscible polycarbonate (PC)/polyvinylidenefluoride (PVDF) pair by a third homopolymer, i.e. polymethylmethacrylate (PMMA), was studied in relation to phase morphology and mechanical properties of the polyblends. Scanning electron microscopy showed a more regular and finer phase dispersion when the original PMMA content in PVDF exceeded 20 wt.%. The premixing of PVDF with ca. 40 wt.% PMMA also had a beneficial effect on mechanical properties, such as ultimate tensile strength, elongation at break, and notched impact strength. All these experimental results are consistent with the interfacial activity of PMMA in the PC/PVDF blends. [less ▲]

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See detailComposition effect on the core-shell morphology and mechanical properties of ternary polystyrene/styrene-butadiene rubber/polyethylene blends
Luzinov, Igor; Xi, K.; Pagnoulle, Christophe et al

in Polymer (1999), 40(10), 2511-2520

The morphology of ternary polystyrene/styrene-butadiene rubber/polyethylene (PS/SBR/PE) blends has been investigated in the limits of a constant content of the major component (PS; 75 wt%) while changing ... [more ▼]

The morphology of ternary polystyrene/styrene-butadiene rubber/polyethylene (PS/SBR/PE) blends has been investigated in the limits of a constant content of the major component (PS; 75 wt%) while changing the weight ratio of the two minor constitutive polymers. A core-shell structure for the dispersed phase has been predicted from the spreading coefficients and observed by transmission electron microscopy. Actually, upon increasing the relative content of PE with respect to SBR, the structure of the dispersed phase changes from a multicore structure to a PE/SBR core-shell morphology. The size of the PE subphase in the mixed dispersed phase increases sharply at a PE content that corresponds to phase inversion in the parent SBR/PE binary blends. The ultimate mechanical properties of these blends are sensitive to the strength of the SBR interphase between PS and PE. Some synergism has been observed in the PE/SBR composition dependence of the tensile strengths at yield and break. [less ▲]

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See detailBiodegradable and biocompatible inorganic-organic hybrid materials: 4. Effect of acid content and water content on the incorporation of aliphatic polyesters into silica by the sol-gel process
Tian, Dong; Blacher, Silvia ULg; Jérôme, Robert ULg

in Polymer (1999), 40(4), 951-957

The extent of poly -caprolactone (PCL) incorporation into silica networks prepared by the sol-gel process depends on the HCl:tetraethoxysilane (TEOS) molar ratio and the H2O:TEOS molar ratio, as well. The ... [more ▼]

The extent of poly -caprolactone (PCL) incorporation into silica networks prepared by the sol-gel process depends on the HCl:tetraethoxysilane (TEOS) molar ratio and the H2O:TEOS molar ratio, as well. The PCL incorporation increases with the concentration of the acid used as the catalyst. Dynamic mechanical analysis (DMA) indicates that increasing the acid concentration or decreasing the water content results in a higher glass transition temperature for the organic component in the hybrid materials, whereas the modulus does not change significantly. Small-angle X-ray scattering (SAXS) data agree with a nanoscopic phase separation of the two constitutive components: the organic polymer and the silica network. The characteristic length of this two-phase structure increases with acid content (except for the lower HCl:TEOS molar ratio of 0.05) and with water content (except for the higher H2O:TEOS molar ratio of 2.0). The structure of the PCL/SiO2 interface is mass fractal and the structure is more open when the acid content is lower or the water content higher. [less ▲]

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See detailStereocomplexation of sPMMA-PBD-sPMMA triblock copolymers with isotactic PMMA. II: Effect of molecular weight
Yu, Jian Ming; Jérôme, Robert ULg

in Polymer (1998), 39(25), 6567-6575

Thermoplastic elastomers consisting of triblock copolymers (MBM) with outer syndiotactic poly(methyl methacrylate) (sPMMA) blocks associated to an inner polybutadiene (PBD) block have been modified by ... [more ▼]

Thermoplastic elastomers consisting of triblock copolymers (MBM) with outer syndiotactic poly(methyl methacrylate) (sPMMA) blocks associated to an inner polybutadiene (PBD) block have been modified by stereocomplexation with isotactic PMMA (iPMMA) at a constant 2/1 sPMMA/iPMMA (or s/i) mixing ratio. Toluene cast films of these stereocomplexes have been studied by thermal analysis as a function of molecular weight of the sPMMA blocks and the iPMMA homopolymer. Although the melting temperature of the stereocomplex (Tm) is independent of molecular weight of the sPMMA blocks ( sPMMA) in the studied range from 7000 to 46 000, the melting enthalpy increases with increasing sPMMA. This effect is, however, erased by the sample annealing at 140°C for 15 h, and a melting enthalpy of cα. 33 J/g total PMMA is then observed whatever the copolymer composition. One melting endotherm is observed in case of low sPMMA. although two melting endotherms are reported for higher sPMMA depending, however, on the heating rate. Two endotherms are indeed observed at small sPMMA as the heating rate is low. Molecular weight of iPMMA has no significant effect on either the melting temperature or the melting enthalpy of the stereocomplexes. Dynamic mechanical analysis has confirmed the phase separation of the complexed triblock copolymers. At constant molecular weight of PBD and iPMMA, stereocomplexation increases the tensile strength of MBM copolymers containing small sPMMA blocks, whereas the opposite effect is observed for longer sPMMA blocks. When the same MBM copolymer is complexed by iPMMA, the tensile properties are independent of the molecular weight of iPMMA at least in the range from 5000 to 74 000. [less ▲]

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