New 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

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 ▲]

Small-angle neutron scattering studies of low-polarity telechelic ionomer solutions. 3. Temperature dependence of the ionic association

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 ▲]

Aggregates formed by amphoteric diblock copolymers in water

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 ▲]

Deformation behavior of weakly segregated block copolymers. 2. Correlation between phase behavior and deformation mechanisms of diblock copolymers

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 ▲]

Controlled ring-opening polymerization of epsilon-caprolactone promoted by "in situ" formed yttrium alkoxides

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 ▲]

Elongation of telechelic ionomers under shear: a rheological and rheo-optical study

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 ▲]

Ring-Opening Polymerization of γ-bromo-ε-caprolactone : A novel route to functionalized aliphatic polyesters

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 ▲]

Study 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

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 ▲]

Mechanical 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

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 ▲]

Highly stereoselective ruthenium-catalyzed ring-opening metathesis polymerization of 2,3-difunctionalized norbornadienes and their 7-oxa analogues

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 ▲]