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See detailMechanical properties of weakly segregated block copolymers. 3. Influence of strain rate and temperature on tensile properties of poly(styrene-b-butyl methacrylate) diblock copolymers with different morphologies
Weidisch, Roland; Stamm, Manfred; Michler, G. H. et al

in Macromolecules (1999), 32(3), 742-750

Poly(styrene-b-butyl methacrylate) diblock copolymers, PS-b-PBMA, with different morphologies are investigated with respect to the influence of strain rate and temperature on tensile properties. In the ... [more ▼]

Poly(styrene-b-butyl methacrylate) diblock copolymers, PS-b-PBMA, with different morphologies are investigated with respect to the influence of strain rate and temperature on tensile properties. In the first part the mechanical properties of bicontinuous and perforated lamellar structure are compared with other morphologies. Diblock copolymers with bicontinuous structures (39% PS) show a much higher tensile strength as well as a higher strain at break than diblock copolymers with lamellar structures (50% PS). In the second part the dependence of tensile properties on strain rate and temperature are discussed for different morphologies. A diblock copolymer with a polystyrene content of 76% PS reveals hexagonally packed PBMA−cylinder, and the tensile strength, strain at break, and Young's modulus exceed the values of pure polystyrene at all measured strain rates. The interesting properties of PS-b-PBMA diblock copolymers are discussed with respect to the phase behavior, interface formation, and chain conformation. [less ▲]

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See detailControlled radical polymerization of (meth)acrylates by ATRP with NiBr2(PPh3)2 as catalyst
Moineau, Georges; Minet, Michaël; Dubois, Philippe ULg et al

in Macromolecules (1999), 32(1), 27-35

NiBr2(PPh3)2 has been found to be an efficient catalyst for the ATRP of methyl methacrylate (MMA) and n-butyl acrylate (n-BuA) initiated by an alkyl halide in the absence of any activator (e.g., Lewis ... [more ▼]

NiBr2(PPh3)2 has been found to be an efficient catalyst for the ATRP of methyl methacrylate (MMA) and n-butyl acrylate (n-BuA) initiated by an alkyl halide in the absence of any activator (e.g., Lewis acid) at 85 °C. The molecular weight distribution of the poly(meth)acrylates is narrow (Mw/Mn = 1.1−1.4). However, some side reactions (more likely coupling reactions) are observed at high monomer conversions in the case of n-BuA. An excess of PPh3 has proved to increase the polymerization rate of MMA while preserving the control of the molecular parameters. When the catalyst/initiator molar ratio is too small (e.g., 0.05), the polymerization rate decreases, the polydispersity increases, and the initiation is less efficient. α-Acid and α-hydroxyl end groups have been successfully attached to the chains by using functional initiators, such as 2-bromo-2-methylpropionic acid and 2,2‘,2‘ ‘-tribromoethanol. Reactivity ratios for the MMA/n-BuA comonomer pair have been measured and found to be close to the values observed for a conventional free-radical polymerization. Diethyl meso-2,5-dibromoadipate has been used as a difunctional initiator for the n-BuA polymerization, leading to α,ω-bromo-poly(n-BuA) of narrow molecular weight distribution. Finally, the thermal stability of PMMA is consistent with the lack of termination reactions, while Tg is as high as 125 °C. [less ▲]

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See detailHighly stereoselective ruthenium-catalyzed ring-opening metathesis polymerization of 2,3-difunctionalized norbornadienes and their 7-oxa analogues
Delaude, Lionel ULg; Demonceau, Albert ULg; Noels, Alfred ULg

in Macromolecules (1999), 32(7), 2091-2103

The ring-opening metathesis polymerization (ROMP) of 2,3-difunctionalized norbornadienes and their 7-oxa analogues catalyzed by [RuCl2(p-cymene)](2) in the presence of trimethylsilyldiazomethane (TMSD ... [more ▼]

The ring-opening metathesis polymerization (ROMP) of 2,3-difunctionalized norbornadienes and their 7-oxa analogues catalyzed by [RuCl2(p-cymene)](2) in the presence of trimethylsilyldiazomethane (TMSD) yields high-trans, highly tactic polymers. A tentative mechanism involving arene loss, carbene formation, and monomer chelation is presented. The ROMP of 2,3-dicarbomethoxynorbornadiene served as a test reaction to investigate the influence of the various experimental parameters (reaction time and temperature, nature of the solvent and catalyst, and TMSD initiation conditions). An all-trans, highly tactic (>79%) polymer was obtained under a wide variety of conditions. Strikingly, the addition of tricyclohexylphosphine had a detrimental influence on the polymerization yield and stereoselectivity. The procedure was successfully applied to various other 2,3-dicarboalkoxynorbornadienes, benzonorbornadiene, and their 7-oxa analogues. In the case of the diester monomers, an increase in the alkyl substituent size led to a decrease of the polymer trans content and tacticity. Because of the ruthenium catalyst's ready availability and marked resistance to oxygen and water, reactions were very easy to set up and to carry out. [less ▲]

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See detailDendrimer-like star block and amphiphilic copolymers by combination of ring opening and atom transfer radical polymerization
Hedrick, James L.; Trollsas, Mikael; Hawker, Craig Jon et al

in Macromolecules (1998), 31(25), 8691-8705

A new type of macromolecular architecture, denoted as dendrimer-like star block copolymers, is reported. These block copolymers are described by a radial geometry where the different generations or layers ... [more ▼]

A new type of macromolecular architecture, denoted as dendrimer-like star block copolymers, is reported. These block copolymers are described by a radial geometry where the different generations or layers are comprised of high molecular weight polymer emanating from a central core. A hexahydroxyl functional core was used as an initiator for the “living” ring opening polymerization (ROP) of ε-caprolactone producing a hydroxyl terminated six arm star polymer with controlled molecular weight and narrow polydispersities (PD < 1.1). Capping these chain ends with dendrons containing activated bromide moieties produced “macro-initiators” for atom transfer radical polymerization (ATRP). Methyl methacrylate was polymerized from these “macro-initiators” in the presence of an organometallic promoter to produce the requisite dendrimer-like star polymers. High molecular weight was obtained with low polydispersities (<1.2). Alternatively, amphiphilic character could be introduced by designing the different layers or generations to be either hydrophobic or hydrophilic. For example, methyl methacrylate (MMA) with either hydroxyethyl methacrylate (HEMA) or methacrylate functional ethylene oxide macromonomers (EO) were polymerized from these “macro-initiators” to provide a hydrophilic outer layer. The use of macromolecular building blocks allows rapid attainment of high polymer in a limited number of steps with purification between transformation requiring only polymer precipitation. [less ▲]

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See detailPhase behavior of diblock copolymers between styrene and n-alkyl methacrylates
Ruzette, A. V. G.; Banerjee, P.; Mayes, A. M. et al

in Macromolecules (1998), 31(24), 8509-8516

In contrast to most diblock copolymers which exhibit the classical upper critical ordering transition (UCOT), polystyrene-b-poly n-butyl methacrylatePS-b-PBMAhas been shown to undergo ordering upon ... [more ▼]

In contrast to most diblock copolymers which exhibit the classical upper critical ordering transition (UCOT), polystyrene-b-poly n-butyl methacrylatePS-b-PBMAhas been shown to undergo ordering upon heating through a lower critical ordering transition (LCOT). Here we report the phase behavior of a family of diblock copolymers formed from styrene and a homologous series of n-alkyl methacrylates, as determined by combined dynamic rheological testing and small-angle neutron scattering (SANS). It is shown that the shortest side chain methacrylates, with the exception of methyl methacrylate, exhibit the LCOT, while for side chains longer than n-butyl, the copolymers exhibit the classical UCOT behavior. Combined group contribution/lattice fluid model calculations of the solubility parameter and specific volume of the corresponding homopolymers qualitatively support these observations. The same calculations were further employed to molecularly design LCOT behavior into a new diblock material consisting of styrene and a random copolymer of methyl and lauryl methacrylate, denoted PS-b-P(MMA-r-LMA). The success of this approach suggests a simple semiquantitative method for predicting and designing the phase behavior of weakly interacting polymer pairs. [less ▲]

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See detailInvestigation of methyl methacrylate and vinyl acetate polymerization promoted by Al(iBu)3/2,2'-bipyridine and Al(iBu)3/2,2'-bipyridine/TEMPO complexes
Granel, Claude; Jérôme, Robert ULg; Teyssié, Philippe et al

in Macromolecules (1998), 31(21), 7133-7141

Results of methyl methacrylate (MMA) and vinyl acetate (VOAc) polymerization using the Al(iBu)3/2,2‘-bipyridine/TEMPO initiating system at room temperature failed to confirm the “living” radical mechanism ... [more ▼]

Results of methyl methacrylate (MMA) and vinyl acetate (VOAc) polymerization using the Al(iBu)3/2,2‘-bipyridine/TEMPO initiating system at room temperature failed to confirm the “living” radical mechanism reported earlier. Several species apparently propagate without control in a normal free radical process and only above a critical initiator concentration. No evidence was found for the penta- and hexacoordinated aluminum species previously suggested, but high conversion to an alkoxyamine was observed. Additionally, mixing Al(iBu)3 and BIPY promotes a variety of reactions involving alkyl and hydride transfers to the aromatic rings forming reduced BIPY products, along with a persistent organoaluminum radical. All these results illustrate that the process is considerably more complicated than postulated before. Conversely, at −78 °C, a single active species excluding the participation of TEMPO has been put in evidence, displaying some “living” characteristics. Several experiments support its anionic nature, as previously suggested by Ikeda. [less ▲]

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See detail4-Methoxypyridine N-Oxide: a new regulator for the controlled free radical polymerization of methyl methacrylate
Detrembleur, Christophe ULg; Lecomte, Philippe ULg; Caille, Jean-Raphaël et al

in Macromolecules (1998), 31(20), 7115-7117

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See detailInfluence of end group and molecular weight on polybutadiene fingerprint secondary ion mass spectra
Vanden Eynde, X.; Bertrand, P.; Dubois, Philippe ULg et al

in Macromolecules (1998), 31(19), 6409-6416

Polybutadiene samples of different molecular weight have been synthesized by anionic polymerization as initiated by sec-butyllithium with low polydispersity and a major content of 1,2-vinyl units. They ... [more ▼]

Polybutadiene samples of different molecular weight have been synthesized by anionic polymerization as initiated by sec-butyllithium with low polydispersity and a major content of 1,2-vinyl units. They have been analyzed by time-of-flight secondary ion mass spectrometry (ToF-SIMS) in order to investigate the sensitivity of this method toward the sec-butyl end group and toward the molecular weight. The SIMS spectra show the characteristic fragment of the end group, C4H9+ at m/z = 57, whose the peak intensity is strongly dependent on the polymer molecular weight, as is the case for almost all the fragment intensities. A model consistent with the peak intensity variations is used to give some new insights into the fragmentation mechanism at the end groups and within the main chain. Moreover, the analysis of the end group fragment allows Mn to be readily determined up to Mn = 4 × 104 from, for example, the Y(53)/Y(57) intensity ratio where Y(53) is the intensity of the deprotonated repeat unit ([M − H]+). Other Mn calibration methods have also been used and are discussed in terms of their accuracy and physical meaning. [less ▲]

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See detailNew ligands for the living high-molecular-weight anionic (co)polymerization of acrylates in toluene at 0°C.1,2 3. Ligation of sec-butyllithium by lithium silanolates
Zundel, Thomas; Teyssié, Philippe; Jérôme, Robert ULg

in Macromolecules (1998), 31(17), 5577-5581

sec-Butyllithium combined with a new family of ligands, (i.e., lithium silanolates), has been used to initiate the ligated anionic polymerization of n-butyl acrylate (BuA) in toluene at low temperature ... [more ▼]

sec-Butyllithium combined with a new family of ligands, (i.e., lithium silanolates), has been used to initiate the ligated anionic polymerization of n-butyl acrylate (BuA) in toluene at low temperature. Compared to other μ-ligands, sBuMe2SiOLi is a more efficient stabilizer of the active centers. Thus, under selectively chosen reaction conditions, the polymerization proceeds quantitatively at −40 °C, producing a high-molecular-weight polymer with narrow-molecular-weight distribution (Mw/Mn < 1.2). When the copolymerization of BuA is initiated by a living {PMMALi, 5·sBuDLi} in toluene at −78 °C, the experimental data agree with a well-controlled block copolymerization reaction, since the final molecular-weight distribution is very narrow (Mw/Mn ≤ 1.1) and the polymerization efficiency very high. [less ▲]

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See detailDiffusive radical entry as the rate-determining step in amphiphilic block polyelectrolyte mediated emulsion polymerization
Leemans, Luc; Jérôme, Robert ULg; Teyssié, Philippe

in Macromolecules (1998), 31(17), 5565-5571

The amphiphilic water soluble block polyelectrolytes PMMA-b-SPGMA and PMMA-b-QPDMAEMA are efficient surfactants for the radical emulsion polymerization. Negatively charged, neutral, and positively charged ... [more ▼]

The amphiphilic water soluble block polyelectrolytes PMMA-b-SPGMA and PMMA-b-QPDMAEMA are efficient surfactants for the radical emulsion polymerization. Negatively charged, neutral, and positively charged entering radicals were used in combination with polyanionically and polycationically tailored PMMA latex particles. It was shown that the rate of polymerization was very high for systems wherein the entering radical species had an electrical charge sign identical with that of the polyelectrolyte corona around the latex particle. PMMA-b-SPGMA turned out to be 4 times as efficient as compared to SDS emulsified MMA polymerization at 0.6 wt %. Systems wherein polyelectrolyte block and entering radical were of opposite sign displayed strongly reduced polymerization rates. When the polyelectrolyte barrier became thick enough, as in the case of a Mn = 26 000 PMMA-b-QPDMAEMA, no more polymerization was observed. The observed polymerization rate effects are discussed in terms of repulsion of equal charge radicals, leading to enhanced mobility and counterion mobility restriction of the radicals of opposite sign to the polyelectrolyte block. In the latter case, this slowed counterion diffusion of radicals of opposite sign leads to premature aqueous phase termination of free radicals and consequently low flux of entering radicals with low rates of polymerization. The experimental results obtained are consistent with the theoretically predicted case, where the “control by aqueous phase growth” theory for the entry of free radicals in latex particles is invalid. [less ▲]

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See detailMorphology of ionic aggregates in carboxylato- and sulfonato-telechelic polyisoprenes as investigated by small-angle x-ray scattering
Sobry, Roger ULg; Fontaine, Frédéric; Ledent, Jean et al

in Macromolecules (1998), 31(13), 4240-4252

Twenty seven samples of carboxylato- and sulfonato-telechelic polyisoprenes associated with various cations (Na, K, Rb, Cs, Mg, Ca, Sr, and Ba) have been investigated by small-angle X-ray scattering. The ... [more ▼]

Twenty seven samples of carboxylato- and sulfonato-telechelic polyisoprenes associated with various cations (Na, K, Rb, Cs, Mg, Ca, Sr, and Ba) have been investigated by small-angle X-ray scattering. The Bragg spacing characteristic of the ionic peak is directly proportional to the root-mean-square end-to-end distance (rrms) of the polyisoprene chain. In the series of sulfonato-telechelic polyisoprenes, the Bragg spacing is approximately equal to rrms, whereas in the series of carboxylato-telechelic polyisoprenes it amounts to 21/2 rrms. It also appears that the ionic aggregates are more likely distributed according to a planar hexagonal network. An original method has been used for the tail-end analysis of the SAXS profile, which is based on the general vertex contribution to the Kirste−Porod law. It results that the ionic aggregates are of an angulous shape. Four different functions have been used to account for the interphase profile between the ionic phase and the polymeric matrix. The ionic aggregates would accordingly contain an average of 10 alkali-metal cations with a tetrahedral stacking, whereas six alkaline-earth-metal cations would be organized according to an equilateral prism. The oxygen atoms of the anionic groups mainly contribute to the width of the interface. The additional peaks observed in the upturn of the curve at very low angles are the signature of a superstructure similar to that one previously observed for carboxylato-telechelic poly(tert-butyl acrylate)s. [less ▲]

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See detailNew ligands for the living isotactic anionic polymerization of methyl methacrylate in toluene at 0°C. 2. 7Li NMR analysis of sec-butyllithium ligated by lithium silanolates
Zundel, Thomas; Zune, Catherine; Teyssié, Philippe et al

in Macromolecules (1998), 31(13), 4089-4092

The mixed associated species {xsBuLi, (y − x)sBuMe2SiOLi} formed by reaction of sec-Butyllithium (sBuLi) with octamethylcyclotetrasiloxane (Me2SiO)4 in toluene have been used to initiate the anionic ... [more ▼]

The mixed associated species {xsBuLi, (y − x)sBuMe2SiOLi} formed by reaction of sec-Butyllithium (sBuLi) with octamethylcyclotetrasiloxane (Me2SiO)4 in toluene have been used to initiate the anionic polymerization of methyl methacrylate (MMA) in that solvent at 0 °C. The active species generated by this new type of initiator have been characterized by 7Li NMR at 0 °C. The 7Li NMR spectra of sBuLi and sBuMe2SiOLi mixtures in toluene show that only one single type of {sBuLi, 5sBuMe2SiOLi} mixed species prevails at [sBuMe2SiOLi]/[sBuLi] molar ratios higher than ca. 21, as result of a large excess of {6sBuMe2SiOLi} species. The 7Li NMR has also concluded to the formation of {PMMALi, 5sBuMe2SiOLi} species upon the addition of MMA to that initiator solution, supporting the theory that only one type of ionic species is active during the MMA conversion. These active centers are stable for at least 1 h at 0 °C as confirmed by 7Li NMR. [less ▲]

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See detailHighly functional branched and dendri-graft aliphatic polyesters through ring opening polymerization
Trollsas, Michaël; Hedrick, James L.; Mecerreyes, David et al

in Macromolecules (1998), 31(9), 2756-2763

Highly branched poly(ε-caprolactones) with novel and well-defined molecular architectures have been synthesized by the use of new multifunctional initiators. The ring-opening polymerization methods used ... [more ▼]

Highly branched poly(ε-caprolactones) with novel and well-defined molecular architectures have been synthesized by the use of new multifunctional initiators. The ring-opening polymerization methods used to prepare these new structures allowed accurate control of molecular weight and narrow molecular weight distributions. In addition, the synthesis of even more complex molecular architectures was possible by the use of 1,4,9-trioxaspiro[4.6]-9-undecanone as a comonomer with ε-caprolactone. After copolymerization, complete deacetalization of the polyester chains into the corresponding ketone groups followed by quantitative reduction formed polymers with hydroxyl pendant groups. With this synthetic strategy, significant additional functionality was introduced. In addition, the pendant hydroxyl groups along the chains can serve as macroinitiators for the further initiation of ε-caprolactone to prepare dendri-graft molecular architectures. The new polymers were characterized by 1H NMR, 13C NMR, and size exclusion chromatography (SEC). 13C NMR spectra clearly showed that the hydroxyl groups of the initiators were fully substituted to give polymers with two, four, and six arms. [less ▲]

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See detailClimbing back up the nucleophilic reactivity scale. Use of cyclosila derivatives as reactivity boosters in anionic polymerization
Zundel, Thomas; Baran, Janusz; Mazurek, Mieczyslaw et al

in Macromolecules (1998), 31(9), 2724-2730

It has been well-known for a very long time that, for anionic homo-polymerization or sequential copolymerization to occur, it is mandatory that the relative nucleophilic reactivity of the initiating ... [more ▼]

It has been well-known for a very long time that, for anionic homo-polymerization or sequential copolymerization to occur, it is mandatory that the relative nucleophilic reactivity of the initiating species be equal to or larger than the one of the (co)monomer. However, the results described in this paper demonstrate that such a classic rule can be circumvented in some cases. Indeed, it is reported for the first time that potassium trimethylsilanolate, and “living” potassium poly(ethylene oxide), both of which are unable to initiate styrene or methyl methacrylate (MMA) polymerization, can be converted from oxyanionic active ends to silyl anionic ones by reacting with cyclic disila derivatives, so allowing the homopolymerization and sequential (co)polymerization of styrene or MMA to proceed in a controlled manner. [less ▲]

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See detailStudy of the propagation center in the anionic polymerization of (meth)acrylic monomers: NMR and MNDO study of the complexes of Di-tert-butyl 2-lithio-2,4,4-trimethylglutarate and of the living poly(tert-butyl methacrylate) oligomers with lithium chloride
Zune, Catherine; Dubois, Philippe ULg; Jérôme, Robert ULg et al

in Macromolecules (1998), 31(9), 2744-2755

Interactions of living oligomers of tert-butyl methacrylate (tBuMA) with a Li counterion and of the model living dimer di-tert-butyl 2-lithio-2,4,4-trimethylglutarate (A) with LiCl (B) were studied in ... [more ▼]

Interactions of living oligomers of tert-butyl methacrylate (tBuMA) with a Li counterion and of the model living dimer di-tert-butyl 2-lithio-2,4,4-trimethylglutarate (A) with LiCl (B) were studied in tetrahydrofuran-d8 (THF-d8) solution by 7Li, 6Li, 1H, and 13C, 1D and 2D, NMR spectroscopy. Di-tert-butyl 2-lithio-2,4,4-trimethylglutarate is shown to form a 1:1 complex with lithium chloride in THF. 1H, 7Li NMR results suggest that a rapid equilibrium between free LiCl and the mixed complex takes place when the molar ratio LiCl:lithiated dimer is higher than 1. From 13C relaxation times, a dimeric aggregation (i.e. A2B2) of the complex is deduced, in full accord with MNDO calculations. Preliminary results are presented for living tBuMA oligomers prepared by initiation with diphenylhexyllithium in the presence of various amounts of lithium chloride. Fast-acquired 13C NMR spectra of the living ends were recorded using 13C-enriched monomer added at the end of the polymerization. Their structure is shown to be affected by the amount of LiCl added and to correspond to an equilibrium between free lithium chloride and a complexed end group. A higher excess of LiCl apparently does not change the nature of the complexed living end. The oligomers exhibit marked self-termination in THF at 273 K. Finally, a correlation of the structure of the living chain ends with the macromolecular parameters of the resulting polymer is attempted. [less ▲]

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See detailStudy of the propagation center in the anionic polymerization of (meth)acrylic monomers: NMR and MO LCAO study of the interaction of Di-tert-butyl 2-lithio-2,4,4-trimethylglutarate and the living poly(tert-butyl methacrylate) oligomers with lithium 2-(2-methoxyethoxy)ethoxide in tetrahydrofuran
Zune, Catherine; Dubois, Philippe ULg; Jérôme, Robert ULg et al

in Macromolecules (1998), 31(9), 2731-2743

Interactions of lithium 2-(2-methoxyethoxy)ethoxide (LiOEEM) with the model dimer di-tert-butyl 2-lithio-2,4,4-trimethylglutarate (A) and the living poly(tert-butyl methacrylate) oligomers (B) were ... [more ▼]

Interactions of lithium 2-(2-methoxyethoxy)ethoxide (LiOEEM) with the model dimer di-tert-butyl 2-lithio-2,4,4-trimethylglutarate (A) and the living poly(tert-butyl methacrylate) oligomers (B) were studied in tetrahydrofuran-d8 at 203−273 K using 1H, 13C, 7Li, and 6Li, 1D and 2D, NMR and ab initio SCF 3-21G and MNDO quantum chemical calculations. LiOEEM is shown to have a strong tendency to self-aggregation, producing dimeric, trimeric, and tetrameric aggregates and competing with its mixed aggregation (or complexation) with A and, in particular, B. When dissolved in THF, LiOEEM as well as its mixtures with A form metastable systems which relax in several days at 258 K into equilibrium. Interaction of LiOEEM with A leads to a system of mixed aggregates LiOEEM1A1, LiOEEM3A1, and possibly LiOEEM2A1 along with the original components, in relative populations depending on the LiOEEM/A molar ratio, temperature, time, and probably other factors of preparation. Probable structures of these complexes are proposed, and the nature of the prevalent bonding is suggested. Experimental results indicate that LiOEEM is unable to convert A completely at moderate excess (up to 4/1 mol/mol). Interaction of LiOEEM with B leads to quite analogous complexes but with even lower yields. There appear to be traces of uncomplexed B even at the LiOEEM/B ratio of 10 mol/mol. This is suggested to produce at least two different kinds of active growth centers in the corresponding ligated anionic polymerization of tert-butyl methacrylate and, consequently, the observed bimodality of the polymeric product. The difference with respect to methyl methacrylate, where LiOEEM ensures an almost ideal living polymerization, is suggested to be due to the steric hindrance of efficient complexation exerted by the tert-butyl group. [less ▲]

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See detailNew ligands for the living isotactic anionic polymerization of methyl methacrylate in toluene at 0°C. 1. Ligation of butyllithium by lithium silanolates
Zundel, Thomas; Teyssié, Philippe; Jérôme, Robert ULg

in Macromolecules (1998), 31(8), 2433-2439

sBuLi and tBuLi have been combined with a new family of ligands, i.e. lithium silanolates, and used as initiators for the ligated anionic polymerization (LAP) of methyl methacrylate (MMA) in toluene at 0 ... [more ▼]

sBuLi and tBuLi have been combined with a new family of ligands, i.e. lithium silanolates, and used as initiators for the ligated anionic polymerization (LAP) of methyl methacrylate (MMA) in toluene at 0 °C. Compared to other known μ-ligands, the accordingly formed Bu(Me2)SiOLi are more efficient stabilizers for the active centers. Under appropriate reaction conditions, a fast polymerization proceeds quantitatively without self-termination at 0 °C and leads to high molecular weight polymer of narrow molecular weight distribution (Mw/Mn < 1.2) and high isotacticity (90% isotactic triads). [less ▲]

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See detailDynamics of poly((dimethylamino)alkyl methacrylate-block-sodium metha-crylate) micelles. Influence of hydrophobicity and molecular architecture on the exchange rate of copolymer molecules
Creutz, Serge; Van Stam, Jan; De Schrijver, Frans C et al

in Macromolecules (1998), 31(3), 681-689

The dynamic stability of the micellar aggregates formed by amphiphilic block copolymers, i.e., poly((dimethylamino)alkyl methacrylate-b-sodium methacrylate), has been investigated by steady-state ... [more ▼]

The dynamic stability of the micellar aggregates formed by amphiphilic block copolymers, i.e., poly((dimethylamino)alkyl methacrylate-b-sodium methacrylate), has been investigated by steady-state fluorescence spectroscopy and size exclusion chromatography. The dynamics of exchange of block copolymer molecules between the micelles, formed in aqueous solution, depend on a manifold of factors, e.g., alkyl substituent in the hydrophobic block, the relation between the hydrophobic and hydrophilic blocks, and the architecture of the block copolymer. All copolymers investigated show a slow unimer exchange with an exchange rate constant on the order of 10-3 s-1, with a difference of a factor of 20 between the fastest and the slowest exchange. It is possible to tune the exchange rate in a controlled way; for instance, an extension or branching of the alkyl chain slows down the exchange rate. The same effect is observed when the hydrophobic/hydrophilic balance of these copolymers is increased or when either the hydrophilic or the hydrophobic moiety of diblocks is divided into two external blocks, leading to a triblock copolymer. [less ▲]

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See detailPoly(2-oxepane-1,5-dione) : a highly crystalline modified poly (epsilon-caprolactone) of a high melting temperature
Tian, Dong; Halleux, Olivier; Dubois, Philippe ULg et al

in Macromolecules (1998), 31(3), 924-927

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