Browsing
     by title


0-9 A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

or enter first few letters:   
OK
Full Text
Peer Reviewed
See detailAnionic polymerization of acrylic monomers. 14. Carbon-13 and lithium-7 NMR characterization of the complexation of methyl α-lithioisobutyrate with various lithium cation-binding ligands in tetrahydrofuran
Wang, Jin-Shan; Jérôme, Robert ULg; Warin, R. et al

in Macromolecules (1994), 27(12), 3376-3382

The aggregation equilibrium and electronic structure of methyl alpha-lithioisobutyrate (MIBLi), a monomeric model structurally corresponding to a living poly(methyl methacrylate) chain end associated with ... [more ▼]

The aggregation equilibrium and electronic structure of methyl alpha-lithioisobutyrate (MIBLi), a monomeric model structurally corresponding to a living poly(methyl methacrylate) chain end associated with a lithium countercation, has been examined by Li-7 and/or C-13 NMR spectroscopy in tetrahydrofuran (THF) in the presence of various lithium cation-binding ligands. The addition of dimethoxyethane (DME), triglyme (glyme-3),12-crown-4 (12-CE-4), and hexamethylphosphoric triamide (HMPA) to coexisting tetrameric and dimeric MIBLi in THF induces an increase in dimeric population in the order DME < glyme-3 < 12-CE-4 <HMPA. That order corresponds to an increasing strength of complexation between MIBLi (lithium cation) and the (solvating) ligands For either tetrameric or dimeric species, moreover, the negative charge distribution around MIBLi does not seem to be significantly modified due to the presence of these complexing agents. In striking contrast, complexation of MIBLi by cryptand 211 (K211) does shift the equilibrium between tetramer and dimer toward the formation of a single monomeric K211-complexed species, which gives rise to ca. 13 and 5 ppm upfield shifts at C(alpha) in the C-13 NMR spectra, compared to tetrameric and dimeric species, respectively. The effect of 12-CE-4/K211 on the original aggretation equilbrium for MIBLi in THF nicely explains the significantly different MWD of PMMA anionically prepared in the presence of each of these ligands. [less ▲]

Detailed reference viewed: 12 (1 ULg)
Full Text
Peer Reviewed
See detailAnionic polymerization of acrylic monomers. 15. Living anionic copolymerization of mixtures of methyl metacrylate and tert-butyl acrylate as promoted by dibenzo-18-crown-6
Wang, Jin-Shan; Jérôme, Robert ULg; Bayard, Philippe et al

in Macromolecules (1994), 27(16), 4615-4620

Although mu-coordinating ligands such as LiCl are effective in promoting the well-controlled living anionic block copolymerization of methyl methacrylate (MMA) and tert-butyl acrylate (tBuA), whichever ... [more ▼]

Although mu-coordinating ligands such as LiCl are effective in promoting the well-controlled living anionic block copolymerization of methyl methacrylate (MMA) and tert-butyl acrylate (tBuA), whichever monomer is first polymerized, it has been previously shown that a copolymerization of mixtures of these two monomers does not proceed as expected, giving poor results in terms of both conversion and molecular weight distribution: that was accounted for by the easy back-biting nucleophilic attack of a highly sensitive methyl ester group by a moderately hindered PtBuA anion. It is now reported that such a situation can be completely modified, when a cation-binding sigma-ligand, i.e., dibenzo-18-CE-6, is used in chelating a sodium counterion and surrounding it with a steric barrier, blocking a large enough space area around the ion pair. In fact, a living copolymerization process of mixtures of MMA and tBuA prevails in THF at -78-degrees-C, in the presence of that Na+/DB-18-CE-6 system. The living copolymer is found, although in a relatively small extent, to be of a statistical type rather than a blocky one or a mixture of two corresponding homopolymers. Furthermore, using the extended Kelen-Tudos method, the monomer reactivity ratios are determined to be r(MMA) = 0.02 and r(tBuA) = 8.81. [less ▲]

Detailed reference viewed: 24 (2 ULg)
Full Text
Peer Reviewed
See detailAnionic polymerization of acrylic monomers. 17. Ligated anionic living polymerization of 2-ethylhexyl acrylate as promoted by polydentate lithium alkoxides
Wang, Jin-Shan; Bayard, Philippe; Jérôme, Robert ULg et al

in Macromolecules (1994), 27(18), 4890-4895

Different initiators combined with a new family of mu/sigma dual ligands, i.e., polydentate alkoxides, were used to initiate the anionic polymerization of 2-ethylhexyl acrylate (2EtHA) at low temperatures ... [more ▼]

Different initiators combined with a new family of mu/sigma dual ligands, i.e., polydentate alkoxides, were used to initiate the anionic polymerization of 2-ethylhexyl acrylate (2EtHA) at low temperatures. It has been found that lithium 2(2-methoxyethoxy) ethoxide (LiOEEM) is the most efficient mu/sigma ligand in promoting a living polymerization of that monomer. Although LiOEEM gives rise to a molecularly well-controlled P2EtHA at -78 degrees C in a 9/1 toluene/THF mixture, i.e., quantitative yield, high initiator efficiency (>90%), and narrow molecular weight distribution (M(w)/M(n) down to 1.05), two-step monomer resumption experiments always lead to a bimodal distribution, suggesting that the LiOEEM-complexed P2EtHA anions are not stable. Nevertheless, a perfectly living 2EtHA anionic polymerization process has been obtained at -100 degrees C, keeping other conditions unchanged. In comparison with other types of ligands, such as LiCl and LiOtBu (both mu-ligands) and DB18CE6 and K222 (both sigma-ligands), it has been further demonstrated that the formation of a stable and bulky active complex is at the origin of the anionic living polymerization of 2EtHA, in agreement with our findings in the case of anionic statistical copolymerization of methacrylate and acrylate. [less ▲]

Detailed reference viewed: 33 (1 ULg)
Full Text
Peer Reviewed
See detailAnionic polymerization of acrylic monomers. 18. NMR characterization of a unique complex between lithium 2-(2-methoxyethoxy) ethoxide and methyl α-lithioisobutyrate
Wang, Jin-Shan; Jérôme, Robert ULg; Teyssié, Philippe

in Macromolecules (1994), 27(18), 4896-4901

A unique ligand-promoted-loose mixed complex MIB-(Li-3(OEEM)(2))(+) has been characterized for the first time by means of NMR spectroscopy in solution. This new complex, which is a dual mu/sigma one, is ... [more ▼]

A unique ligand-promoted-loose mixed complex MIB-(Li-3(OEEM)(2))(+) has been characterized for the first time by means of NMR spectroscopy in solution. This new complex, which is a dual mu/sigma one, is obviously different from either a simple tight mu-mixed complex, such as nMIBLi.mX (X = Cl or OtBu), or a sigma-cation-binding one with mole charge separation, such as K211/MIBLi. It originates from a simultaneous dual complexation (mu/sigma) of MIBLi by both the lithium alkoxide (mu-mixed complexation) and the chelating polyether components (sigma-cation-binding complexation) of LiOEEM. Furthermore, it has been demonstrated; that, whichever the solvent, i.e., toluene, a 9/1 toluene/THF mixture, or THF, complexation of MIBLi by greater than or equal to 2 mol equiv of LiOEEM produces the same type of complex, i.e., MIB-(Li-3(OEEM)(2))(+), suggesting that, in this strong complex, the lithium cations are strongly coordinated by the ligand. [less ▲]

Detailed reference viewed: 20 (1 ULg)
Full Text
Peer Reviewed
See detailAnionic polymerization of acrylic monomers. 19. Effect of various types of ligands other than lithium chloride on the stereochemisty of anionic polymerization of methyl methacrylate
Wang, Jin-Shan; Jérôme, Robert ULg; Teyssié, Philippe

in Macromolecules (1994), 27(18), 4902-4907

The effect of several types of ligands, i.e., 12-CE4 (1), K211 (2), LiOtBu (3), and LiOEEM (4), on the stereochemistry of MMA anionic polymerization at -78 degrees C in various solvents, i.e., toluene ... [more ▼]

The effect of several types of ligands, i.e., 12-CE4 (1), K211 (2), LiOtBu (3), and LiOEEM (4), on the stereochemistry of MMA anionic polymerization at -78 degrees C in various solvents, i.e., toluene, THF, and a 9/1 toluene/THF mixture, has been studied. Similar to the LiCl-complexed system, the stereoregularity of MMA polymerization in the presence of these additives is seemingly controlled by association/complexation equilibria among associated, nonassociated, and ligand-complexed active species. Accordingly, complexation of active species by sigma-chelating ligands such as 12-CE4 and K211 simply shifts the association equilibrium toward the formation of ligand-complexed (nonassociated) species, giving preferably syndiotactic placements (rr) in a 9/1 toluene/THF mixture as well as in toluene. However, the effect of a mu-type ligand, i.e., LiOtBu, seems more complicated. In THF and toluene, similar to ligand-free systems, highly syndiotactic and isotactic PMMAs are produced, respectively, implying the existence of different types of stereoselective LiOtBu-complexed species. In a 9/1 toluene/THF mixture, moreover, addition of LiOtBu gives rise to an increase in isotactic placements (mm) and matches the values observed in toluene. This is in striking contrast to the LiCl-added system, for which it has been tentatively proposed that a meso or raceme placement might also critically depend on the aggregation degree of the living chain in the complexed species. Nevertheless, a mu/sigma dual ligand, i.e., LiOEEM, gives rise to an almost identical stereoregularity (i.e., highly syndiotactic) whatever the solvent used, well consistent with the involvement of the same type of active complex. [less ▲]

Detailed reference viewed: 24 (2 ULg)
Full Text
Peer Reviewed
See detailAnionic polymerization of acrylic monomers. 21. Anionic sequential polymerization of 2-ethylhexyl acrylate and methyl methacrylate
Wang, Jin-Shan; Jérôme, Robert ULg; Bayard, Philippe et al

in Macromolecules (1994), 27(18), 4908-4913

A mixed complex of a polydentate lithium alkoxide, i.e., lithium 2-(2-methoxyethoxy) ethoxide (LiOEEM), and of a mono- or bisfunctional organolithium initiator, i.e., (diphenylmethyl)lithium (DPMLi) or ... [more ▼]

A mixed complex of a polydentate lithium alkoxide, i.e., lithium 2-(2-methoxyethoxy) ethoxide (LiOEEM), and of a mono- or bisfunctional organolithium initiator, i.e., (diphenylmethyl)lithium (DPMLi) or lithium naphthalene/diphenylethylene, has been used to synthesize well-controlled AB (BA), ABA, and BAB block copolymers of methylmethacrylate (MMA) (A) and 2-ethylhexyl acrylate (2EtHA) (B), irrespective of the monomer addition order. Although the 2EtHA block copolymerization initiated with monofunctional living PMMA macroanions at -78 degrees C in a 75/25 toluene/THF mixture gives rise to a precisely-tailored PMMA-b-P2EtHA diblock polymer, the reverse sequence, i.e.,from P2EtHA anions to the MMA type monomer, always results in contamination by homo-P2EtHA. This has been interpreted in terms of the short shelf lifetime of P2EtHA anions present. Nevertheless, a pure P2EtHA-b-PMMA type diblock copolymer can be produced at -100 degrees C, while keeping other conditions unchanged. More importantly, a well-controlled PMMA-b-P2EtHA-b-PMMA triblock copolymer has been prepared through a three-stage process with a monofunctional initiator, actually providing a potential pathway toward the direct synthesis of a novel type of fully acrylic thermoplastic elastomer, instead of the more complicated hydrolysis/transalcoholysis process previously demonstrated by us. [less ▲]

Detailed reference viewed: 25 (1 ULg)
Full Text
Peer Reviewed
See detailAnionic polymerization of acrylic monomers. 6. Synthesis, characterization, and modification of poly(methyl methacrylate)-poly(tert-butyl acrylate) di- and triblock copolymers
Varshney, Sunil K; Jacobs, Christian; Hautekeer, Jean-Paul et al

in Macromolecules (1991), 24(18), 4997-5000

Poly(methyl methacrylate)-b-poly(tert-butyl acrylate) (PMMA-b-PtBA) copolymers have been successfully synthesized by the sequential anionic polymerization of methyl methacrylate (MMA) and tert-butyl ... [more ▼]

Poly(methyl methacrylate)-b-poly(tert-butyl acrylate) (PMMA-b-PtBA) copolymers have been successfully synthesized by the sequential anionic polymerization of methyl methacrylate (MMA) and tert-butyl acrylate (tBA) in THF at -78-degrees-C. Although the order of monomer addition makes a difference on the initiation efficiency, it has no significant effect on the final achievement. Mono- and bifunctional initiators based on alkali metals can be used. When the initiators are modified by LiCl as a ligand, the polymerization of each block appears to be living, the molecular weight and composition can be predicted, and the molecular weight distribution is narrow. Size exclusion chromatography supports the absence of homo-PtBA in the PtBA-b-PMMA samples. The PtBA blocks can be quantitatively hydrolyzed into polyacid ones as supported by titration and H-1 NMR analysis. [less ▲]

Detailed reference viewed: 27 (1 ULg)
Full Text
Peer Reviewed
See detailAnionic polymerization of acrylic monomers. 8. Synthesis and characterization of (meth)acrylic end-functionalized polymers: macromonomers and telechelics
Varshney, Sunil K; Bayard, Philippe; Jacobs, Christian et al

in Macromolecules (1992), 25(21), 5578-5584

Tailor-made poly(tert-butyl acrylate) macromonomers, which are useful building blocks for the synthesis of comb or multiblock copolymers, have been successfully synthesized by deactivation of living PtBA ... [more ▼]

Tailor-made poly(tert-butyl acrylate) macromonomers, which are useful building blocks for the synthesis of comb or multiblock copolymers, have been successfully synthesized by deactivation of living PtBA macroanions with suitable electrophiles bearing either styrene or methacrylic unsaturation. Mono- or bifunctional initiators such as sec-butyllithium or naphthalenyllithium can be used. When these initiators were modified by LiCl as a mu-type ligand, the macroanions which are known to be living were functionalized with high efficiency. Characterization of the various macromonomers was performed using H-1 NMR spectroscopy and SEC. [less ▲]

Detailed reference viewed: 22 (1 ULg)
Full Text
Peer Reviewed
See detailAnionic polymerization of acrylic monomers. V. Synthesis, characterization and modification of polystyrene-poly(tert-butyl acrylate) di- and triblock copolymers
Hautekeer, Jean-Paul; Varshney, Sunil K; Fayt, Roger et al

in Macromolecules (1990), 23(17), 3893-3898

Detailed reference viewed: 34 (2 ULg)
Full Text
Peer Reviewed
See detailAnionic polymerization of methacrylate monomers initiated by lithium dialkylamides
Antoun, Sayed; Teyssié, Philippe; Jérôme, Robert ULg

in Journal of Polymer Science. Part A, Polymer Chemistry (1997), 35(17), 3637-3544

The anionic polymerization of methacrylate monomers has been investigated with lithium dialkylamides as initiators in THF and toluene, respectively. Theoretical arguments and previous studies of mixed ... [more ▼]

The anionic polymerization of methacrylate monomers has been investigated with lithium dialkylamides as initiators in THF and toluene, respectively. Theoretical arguments and previous studies of mixed aggregates of lithiated organic compounds support the complexity of these systems. Lithium diisopropylamide (LDA) shows the highest initiation efficiency (e.g., f = 75% in THF at -78°C). Interestingly enough, lithium chloride has a remarkable beneficial effect on the methacrylates polymerization in THF at -78°C, due to the formation of 1 : 1 mixed dimer with LDA, which promotes a well-controlled anionic polymerization (Mw/Mn = 1.05) with a high initiation efficiency (94%). The less bulky lithium-diethylamide (LDEA) is much less efficient (f = 26%), essentially as a result of some associated dormant species and side reactions on the carbonyl group of MMA. Although various types of ligands have been screened, no remarkable improvement of LDEA efficiency has been observed. Lithium bis(trimethylsilyl)amide (LTMSA) has also been used to increase the steric hindrance of the initiator. This compound is, however, unable to initiate the methacrylates polymerization, more likely because of a too low basicity and a too strong Li - N bond. © 1997 John Wiley [less ▲]

Detailed reference viewed: 45 (1 ULg)
Full Text
Peer Reviewed
See detailAnionic polymerization of methacrylic monomers: characterization of the propagating species
Zune, Catherine; Jérôme, Robert ULg

in Progress in Polymer Science (1999), 24(5), 631-664

Ligation of the anionic species responsible for the polymerization (LAP) of alkyl(meth)acrylates has much contributed to improve polymerization control. This ligated anionic polymerization has been ... [more ▼]

Ligation of the anionic species responsible for the polymerization (LAP) of alkyl(meth)acrylates has much contributed to improve polymerization control. This ligated anionic polymerization has been firstly studied by using model compounds, such as low molecular weight lithium ester enolates. Recently, effort has been devoted to the direct analysis of the species that propagate the anionic polymerization of (meth)acrylates. In addition to IR, multinuclear NMR spectroscopy has been very instrumental in the elucidation of the structure and aggregation of the active species and how these characteristic features are modified by the addition of various types of ligands. This substantial progress in the characterization of the polyalkyl(meth)acrylate anions, ligated or not, is reported in this review. [less ▲]

Detailed reference viewed: 77 (4 ULg)
Full Text
Peer Reviewed
See detailAnionic polymerization of pivalolactone initiated by alkali metal alkoxides
Jedlinski, Zbigniew; Kurcok, Piotr; Kowalczuk, Marek et al

in Macromolecules (1995), 28(21), 7276-7280

Polymerization of pivalolactone (alpha,alpha-dimethyl-beta-propiolactone) initiated with alkali metal alkoxides has been studied. It has been revealed that after addition of an alkoxide anion, from the ... [more ▼]

Polymerization of pivalolactone (alpha,alpha-dimethyl-beta-propiolactone) initiated with alkali metal alkoxides has been studied. It has been revealed that after addition of an alkoxide anion, from the initiator, onto the carbonyl carbon atom of the monomer the selective cleavage of the acyl-oxygen bond of the monomer leads to the formation of alkoxide propagating species. Thus, it has been demonstrated that, in contrast to alpha-unsubstituted beta-lactones and higher lactones, the anionic polymerization of pivalolactone proceeds through either alkoxide or carboxylate propagation centers, depending on the nature of initiator used, i.e. an alkoxide or a carboxylate, respectively. In the former case, however, cyclic oligomers are also formed which are unusual in the anionic polymerization of other beta-lactones. This indicates that, whatever the lactone ring size (four-, six-, or seven-membered lactones), intramolecular transesterification reactions can take place if alcoholate ions are propagating species. [less ▲]

Detailed reference viewed: 41 (6 ULg)
Full Text
Peer Reviewed
See detailAnionic polymerization of primary acrylates as promoted by Lithium 2-(2-Methoxyethoxy) ethoxide
Nugay, Nihan; Nugay, Turgut; Jérôme, Robert ULg et al

in Journal of Polymer Science. Part A, Polymer Chemistry (1997), 35(2), 361-369

Some primary acrylates, such as methyl, ethyl, n-butyl, and n-nonyl acrylate (MA, EA, nBuA and nNonA, respectively) have been anionically polymerized by using diphenylmethyl lithium (DPMLi) as an ... [more ▼]

Some primary acrylates, such as methyl, ethyl, n-butyl, and n-nonyl acrylate (MA, EA, nBuA and nNonA, respectively) have been anionically polymerized by using diphenylmethyl lithium (DPMLi) as an initiator, in the presence of a chelating - dual ligand, i.e., a polydentate lithium alkoxide, at low temperature. It has been found that lithium 2-(2-methoxyethoxy) ethoxide (LiOEEM) is a very efficient ligand in preventing the anionic polymerization of these monomers from being disturbed by significant secondary transfer and termination reactions. Even for the difficult cases of ethyl and methylacrylate, that approach provides high polymerization yields and low polydispersity, allowing the molecular weight to be predetermined. LiOEEM/initiator molar ratio, solvent polarity, temperature and monomer concentration have proved to be key parameters in the control of the polymerization process. The efficiency of that control is however dependent on the monomer structure and improves with the length of the n-alkyl substituent, i.e., MA < EA < nBuA < nNonA. [less ▲]

Detailed reference viewed: 37 (2 ULg)
Full Text
Peer Reviewed
See detailAnionic polymerization of various methacrylates initiated with LiCl-complexed sBuLi
Antoun, S.; Wang, Jin-Shan; Jérôme, Robert ULg et al

in Polymer (1996), 37(25), 5755-5759

A simple alkyl lithium initiator (sBuLi) complexed with LiCl (10 molar equiv.) has been used to initiate the anionic polymerization of various methacrylic monomers, i.e. methyl methacrylate (MMA), tert ... [more ▼]

A simple alkyl lithium initiator (sBuLi) complexed with LiCl (10 molar equiv.) has been used to initiate the anionic polymerization of various methacrylic monomers, i.e. methyl methacrylate (MMA), tert-butyl methacrylate (tBuMA), glycidyl methacrylate (GMA), and dimethyl amino ethyl methacrylate (DMAEMA) in tetrahydrofuran at -78°C. Only the homopolymerization of tBuMA proceeds in a living manner, as evidenced by both the linear plot of experimental molecular weight (Mnexp) vs theoretical ones (Mncal,) (slope % 0.93) and monomer resumption experiments. However, three types of block copolymers, i.e. PtBuMA-b-PMMA, PtBuMA-b-PGMA, PtBuMA-b-PDMAEMA, have been successfully synthesized with a predictable molecular weight, and narrow molecular weight distribution. [less ▲]

Detailed reference viewed: 82 (2 ULg)
Full Text
Peer Reviewed
See detailAnionic synthesis of [1,4-poly(diene)-b-syndiotactic poly(methyl methacrylate)] diblock copolymers: 7Li NMR study of the intermediate reaction of lithium poly(diene) anion with 1,1-diphenylethylene
Zune, Catherine; Dubois, Philippe ULg; Jérôme, Robert ULg et al

in Macromolecular Chemistry and Physics (1999), 200(2), 460-467

The end-capping with 1,1-diphenylethylene (DPE) of living 1,4-poly(diene) lithiated anions prepared in cyclohexane (Chx) and toluene is a major but poorly controlled step in the synthesis of syndiotactic ... [more ▼]

The end-capping with 1,1-diphenylethylene (DPE) of living 1,4-poly(diene) lithiated anions prepared in cyclohexane (Chx) and toluene is a major but poorly controlled step in the synthesis of syndiotactic poly(methyl methacrylate) (sPMMA) containing block copolymers. The kinetics of the reaction have been studied by means of 7Li NMR not only in Chx and toluene but also in their mixtures with polar solvents, since the solvent polarity must be increased for MMA to be predominantly converted into sPMMA. Although the addition of a polar solvent (tetrahydrofuran (THF), diethyl ether) to Chx and toluene is known to increase the reactivity of living polymeric anions, contaminating lithium salts, such as lithium hydroxide, slow down the end-capping reaction even when 10 vol.-% polar solvent is added. Moreover, the polymeric diphenylalkyllithium anions are unstable in 1/9 (v/v) THF/Chx mixture, as a result of the nucleophilic attack of THF. On the basis of all these observations, new experimental conditions are proposed for improving the control of the anionic block copolymerization of 1,3-dienes and MMA to yield 1,4-poly(diene) and sPMMA containing block copolymers. [less ▲]

Detailed reference viewed: 47 (8 ULg)
Full Text
Peer Reviewed
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 ▲]

Detailed reference viewed: 48 (1 ULg)
Full Text
Peer Reviewed
See detailAnionically prepared poly(epsilon-caprolactam-co-epsilon-caprolactone) and poly(epsilon-caprolactam-co-delta-valerolactone) copolymers: thermal and mechanical properties
Toncheva, Natalia ULg; Jérôme, Robert ULg; Mateva, Rosa

in European Polymer Journal (2011), 47(2), 238-247

Thermal and representative physico-mechanical properties of newly prepared poly[(ε-caprolactam)-co-(ε-caprolactone)] and poly[(ε-caprolactam)-co-(δ-valerolactone)] copolymers were studied. The copolymers ... [more ▼]

Thermal and representative physico-mechanical properties of newly prepared poly[(ε-caprolactam)-co-(ε-caprolactone)] and poly[(ε-caprolactam)-co-(δ-valerolactone)] copolymers were studied. The copolymers were synthesized by anionic polymerization of ε-caprolactam activated by isocyanate end-capped oligomeric aliphatic polyesters designated as the macroactivators (MAs). Type, concentration and molecular weight of the MAs were varied, which resulted in copolymers with different structure and properties. The impact of the new MAs used in this study on the glass transition temperature and the melting temperature of poly-ε-caprolactam was investigated by DSC. DMTA was used to analyze the effect of copolymerization on the storage modulus (E′) and tan δ of poly-ε-caprolactam. Conventional and high-resolution TGA data revealed that all the synthesized polyesteramides possess good thermal stability. Mechanical properties were studied by notched impact and tensile testing. According to the experimental data the impact toughness increase with the MA content, being six time higher compared to the poly(ε-caprolactam) in the best situation. Water absorption was also considered in relation to the composition of the copolymers. [less ▲]

Detailed reference viewed: 220 (9 ULg)
Peer Reviewed
See detailAnisocoria and Cerebro-Vascular Diseases
Martin, Didier ULg

Conference (2006, November 22)

Detailed reference viewed: 7 (0 ULg)
Full Text
Peer Reviewed
See detailAnisotropic AC behavior of multifilamentary Bi-2223/Ag tapes
Fagnard, Jean-François ULg; Vanderbemden, Philippe ULg; Cloots, Rudi ULg et al

in IEEE Transactions on Applied Superconductivity (2003), 13(2, Part 3), 2976-2979

In this communication, we report on the anisotropy of the superconducting properties of multifilamentary Bi-based tapes experimentally investigated by AC magnetic susceptibility measurements. The ... [more ▼]

In this communication, we report on the anisotropy of the superconducting properties of multifilamentary Bi-based tapes experimentally investigated by AC magnetic susceptibility measurements. The susceptibility X = X' - jX" was measured using a commercial system and a couple of orthogonal pick-up coils. The X'' vs. temperature curves were shown to exhibit two peaks. The smaller of the peaks, occurring near T = 72 K, was only visible for particular field directions and within a given frequency window. Such results point out the role played by the phase difference between the applied magnetic field and the internal magnetic field seen by the filaments. (C) 2003 IEEE. [less ▲]

Detailed reference viewed: 66 (29 ULg)