| 1. |
- Aasmundtveit, K.E., et al.
(författare)
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Structural anisotropy of poly(alkylthiophene) films
- 2000
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 33:8, s. 3120-3127
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Tidskriftsartikel (refereegranskat)abstract
- The structural anisotropy of various poly(alkylthiophene) films have been studied by X-ray diffraction, using both conventional methods and synchrotron radiation at grazing incidence. Solution-cast films orient with the side chains preferably normal to the film surface, whereas spin-cast films of nonstereoregular material orient with both the main and the side chains in the film plane. For thick (10-50 µm) solution-cast films, the degree of orientation depends strongly on the solvent used for casting, and on the stereoregularity of the polymer, films of stereoregular materials being more oriented than those of nonregular materials. The most oriented nonregular films are those cast from mixtures of chloroform and tetrahydrofuran. Thin (50-500 nm) solution-cast films are more oriented than the thicker ones, and the effects of different stereoregularity or different casting solvents are small. For spin-cast films, the degree of orientation is independent of substrate and solvent. Spin-cast films of stereoregular material have two different phases: One with the side chains normal to the substrate, and another where they are parallel to the substrate. The diffraction peaks of spin-cast poly(octylthiophene) narrow considerably upon heating.
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| 2. |
- Aasmundtveit, K.E., et al.
(författare)
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Structural ordering in phenyl-substituted polythiophenes
- 2000
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 33:15, s. 5481-5489
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Tidskriftsartikel (refereegranskat)abstract
- Various substituted poly(phenylthiophene)s have been studied by X-ray diffraction. They are semicrystalline, with very different degrees of crystallinity. Those with para-substituted phenyl groups have a low degree of crystallinity, whereas those with ortho-substituted phenyl groups are more crystalline. The most crystalline materials in this study have two equally long substituents on the phenyl ring, one at the ortho position and the other at the ortho or meta position on the opposite side of the phenyl ring. Poly(3-(2,5-dioctylphenyl)thiophene) (PDOPT) was most thoroughly studied, and a structural model is proposed. The structure of PDOPT is quite different from previously studied substituted polythiophenes in that the octyl side chains are directed normal to the thiophene planes. In this way, the conjugated polymer chains are kept separated from each other. Solution-cast and spin-cast PDOPT films are anisotropic, with the octyl side chains oriented normal to the film surface in both cases. This is contrary to the situation for poly(3-alkylthiophene)s, where solution-cast and spin-cast films orient in different ways.
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| 3. |
- Akinchina, Anna, et al.
(författare)
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Monte Carlo simulations of polyion-macroion complexes. 1. Equal absolute polyion and macroion charges
- 2002
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 35:13, s. 5183-5193
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Tidskriftsartikel (refereegranskat)abstract
- Intermolecular structures of complexes formed between a charged polymer and a spherical and oppositely charged macroion have been studied by employing the primitive model solved by Monte Carlo simulations. The strong-complex case involving a polyion and a macroion with equal absolute charges and without small ions was considered. The influence of the polyion flexibility with a bare persistence length ranging from 7 to 1000 Angstrom for four different systems characterized by different polyion linear charge densities and macroion sizes has been examined. Radial distributions, polyion bead complexation probabilities, loop, tail, and train characteristics, and energetic analysis have been performed. The strongest and most compact complex, involving a collapsed polyion wrapping the macroion, was formed for a semiflexible chain. As the stiffness was increased, this state was transformed into a range of different structures comprising "tennis ball seam"-like, solenoid, multiloop ("rosette"), and single-loop arrangements as well as structures involving only a single polyion-macroion contact region.
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| 4. |
- Algers, John, et al.
(författare)
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Free volume and density gradients of amorphous polymer surfaces as determined by use of a pulsed low-energy positron lifetime beam and PVT data
- 2004
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 37:11, s. 4201-4210
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Tidskriftsartikel (refereegranskat)abstract
- Density gradient widths at the polymer-vacuum surfaces of poly(methyl methacrylate), styrene-co-acrylonitrile, and styrene-co-maleic anhydride were quantified to 2, 5, and 4 rim, respectively, by use of a pulsed low-energy positron lifetime beam and to approximately 1.5 nm for all three polymers on the basis of theoretical predictions from pressure-volume-temperature (PVT) data, making use of the Cahn-Hilliard theory of inhomogeneous systems in conjunction with the Sanchez-Lacombe lattice fluid theory. Excellent agreement between the two methods was found for the homopolymer, whereas for the copolymers, the former method gave larger density gradient widths, a result attributed to the surface orientation of the less polar polymer segments, which the theoretical predictions did not take into account. As has been previously proposed, the discrepancy between the depth ranges of the surface effects on density and the glass transition temperature (T-g) is suggested to result from a coupling between the dynamics of adjoining polymer segments, canceling a direct relationship between local density profile rho(z) and local T-g(z) as a function of distance z from the free surface.
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| 5. |
- Algers, John, et al.
(författare)
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Free volume determination of azobenzene-PMMA copolymer by a pulsed low-energy positron lifetime beam with in-situ UV illumination
- 2004
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 37:21, s. 8035-8042
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Tidskriftsartikel (refereegranskat)abstract
- The free volume properties of a poly(methyl methacrylate)-azobenzene copolymer were for the first time directly probed by use of a low-energy positron lifetime beam with in-situ excitation capabilities, showing that the free volume cavity size was not appreciably influenced by photoisomerization and thermal isomerization in the temperature range 34-180 degreesC. lsomerization is therefore suggested to occur without any molecular rearrangement of the glassy polymer matrix, which would also account for the lack of any shift to shorter wavelengths for the photoisomerization occurring in a glassy polymer in comparison to a chloroform solution. A decrease in the thermal isomerization rate at room temperature caused by the glassy polymer is explained in terms of a model in which only a fraction of the azobenzene is free to isomerize. The cis-azobenzene was found to be an efficient inhibitor of positronium formation, which enabled measurements of thermal isomerization rates and changes in the steady-state concentration of cis-azobenzene for an illuminated sample as a function of temperature.
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| 6. |
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| 7. |
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| 8. |
- Busson, P., et al.
(författare)
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Ferroelectric liquid crystalline dendrimers : Synthesis, thermal behavior, and electrooptical characterization
- 2001
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 34:5, s. 1221-1229
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Tidskriftsartikel (refereegranskat)abstract
- The preparation and characterization of a series of novel ferroelectric liquid crystalline dendrimers are presented. End-capping of 1-, 2-, and 3-generation dendrimers based on 2,2-bis(hydroxymethyl)propionic acid with mesogens gave surface-functionalized liquid crystalline compounds with 6, 12, and 24 mesogen-containing units, respectively. 4 -((R)-1-Methylheptyloxy)phenyl 4-(4 '-[10(hydroxycarbonyl)decyloxyl phenyl)benzoate was synthesized and used as a mesogen-containing unit. The purity and structure of each compound were determined by H-1 NMR spectroscopy, size exclusion chromatography, and elemental analysis. Differential scanning calorimetry and optical microscopy were used to investigate the mesomorphic properties of the mesogen-functionalized dendrimers. The materials displayed a variety of mesophases, including the smectic C* phase. All the liquid crystalline dendrimers showed ferroelectricity, and tilt angle and spontaneous polarization measurements were performed. The obtained results show that the ferroelectric properties of the materials are independent of the generation number of the dendritic scaffold.
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| 9. |
- Busson, P., et al.
(författare)
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Preparation of mesogen-functionalized dendrimers for second-order nonlinear optics
- 2002
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 35:5, s. 1663-1671
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Tidskriftsartikel (refereegranskat)abstract
- Liquid crystalline dendrimers with peripheral mesogen-containing units have been prepared. Multistep synthesis with several selective reactions was used in the preparation of the mesogen-containing molecules, 4-[10-(hydroxycarbonyl)decyloxy]phenyl 4-[4'-(2-(R)-octyloxy)-3'-nitrophenyl]benzo ate and 4-[10-(hydroxycarbonyl)decyloxy]biphenyl 4-[4'-(2-(R)-octyloxy)-3'-nitrophenyl]benzoate. Both molecules possessed an electron-accepting nitro group placed perpendicular to the long axis of the molecules in order to enhance the nonlinear optical activity. A second generation hydroxyl functional aliphatic dendrimer based on the dihydroxy acid, 2,2-bis(hydroxymethyl)propionic acid, was used as dendritic scaffold and was subsequently functionalized with the aforementioned groups. The purity and structure of the two liquid crystalline dendrimers were determined by H-1 NMR spectroscopy, size exclusion chromatography, and elemental analysis. The synthesis of both the mesogen-containing units and the liquid crystalline dendrimers is described in detail. Investigation of the liquid crystalline properties of the materials by differential scanning calorimetry and optical microscopy showed that they exhibited different mesophases, including the chiral smectic C phase. Ferroelectric switching was observed in this tilted phase, and electrooptical properties, including tilt angle and spontaneous polarization measurements, were investigated. Finally, the nonlinear optical properties of one of the materials were preliminary characterized.
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| 10. |
- Carlmark, Anna, et al.
(författare)
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ATRP of dendronized aliphatic macromonomers of generation one, two, and three
- 2004
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 37:20, s. 7491-7496
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Tidskriftsartikel (refereegranskat)abstract
- Atom transfer radical polymerization (ATRP) of dendritic, aliphatic macromonomers has been investigated. The macromonomers were based on acrylate functionalized 2,2-bis(methylol)propionic acid (bis-MPA) dendrons, with a flexible spacer of 10 carbons incorporated in the structure in between the polymerizable group and the dendritic wedge. Dendronized polymers of generation one, two, and three were successfully synthesized by ATRP. The polymerizations proceeded until over 80% conversion was reached, while maintaining control over polydispersity index (PDI). Plots of ln([M](0)/[M]) vs time for the polymerization of all three macromonomers showed a linear dependence, indicating that the number of propagating radicals in the reaction solution was constant throughout the reaction, when ethyl 2-bromopropionate (EBrP) was used as an initiator (i.e., radical termination was negligible). All of the resulting polymers had low PDI values and molecular weight close to the theoretical ones. The products were analyzed by H-1 and C-13 NMR spectroscopies, size exclusion chromatography (SEC), differential scanning calorimetry (DSC), and matrix-assisted laser desorption-ionization time-of-flight (MALDI-TOF).
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| 11. |
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| 12. |
- Chronakis, IS, et al.
(författare)
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Thermoreversible gels of hydrophobically modified hydroxyethyl cellulose cross-linked by amylose
- 2002
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 35:10, s. 4113-4122
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Tidskriftsartikel (refereegranskat)abstract
- Aqueous mixtures of hydrophobically modified hydroxyethyl cellulose (HMHEC) or unmodified hydroxyethyl cellulose (HEC), with amylose (AM) or potato amylopectin (PAP), have been investigated by rheology, turbidity, and H-1 NMR measurements. It is concluded that the AM molecules cross-link HMHEC chains by forming helical inclusion complexes with the hydrophobic side chains of HMHEC, leading to thermoreversible, elastic, and thixotropic gels at ambient temperatures. The complexation ability, the setting-melting temperature of the AM-HMHEC complexes, the strength of the association, and the viscoelastic behavior of the gels vary with the polymer concentrations, the pH, and the preparation method. AM-HMHEC complexes were obtained at a pH range of 7-12.5, but a maximum storage modulus was observed at pH approximate to 10. The AM-HMHEC complexation is modified or completely abolished by the addition of surfactant. A weak synergistic interaction was found for mixtures of PAP with HNIHEC. No complexation was observed between HEC and either AM or PAP.
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| 13. |
- Colombini, Didier, et al.
(författare)
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Direct and reverse mechanical modeling of an alkyd acrylic hybrid system: A morphological study
- 2004
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 37:7, s. 2596-2602
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Tidskriftsartikel (refereegranskat)abstract
- Mechanical modeling and dynamic mechanical analysis were associated to investigate the viscoelastic properties of an alkyd acrylic hybrid system in connection with its morphology, which was characterized by transmission electron microscopy. Theoretical predictions based on the interlayer model used in direct mode were successfully combined with the experimental viscoelastic data to lead to relevant additional information about the complex particulate morphology of the hybrid system. Thus, using direct mechanical modeling, it was concluded that the experimental response of the alkyd acrylic hybrid system to a sinusoidal mechanical stress corresponds to the mechanical response of a sample whose morphology involves a acrylic-rich interphase between continuous and dispersed alkyd-rich domains. For the very first time, the interlayer model was then used in reverse mode in order to separate the actual viscoelastic properties of such a acrylic-rich interphase from those experimentally obtained for the alkyd acrylic hybrid system. The differences in these extracted viscoelastic properties, when compared to those of the pure latex film, were presented as reflecting the changes in the molecular mobility of the macromolecules resulting from the mutual influence of the phases in the multiphase hybrid material.
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| 14. |
- Colombini, Didier, et al.
(författare)
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Influence of the particle size and particle size ratio on the morphology and viscoelastic properties of bimodal hard/soft latex blends
- 2004
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 37:18, s. 6865-6873
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Tidskriftsartikel (refereegranskat)abstract
- The morphology and viscoelastic properties of films prepared from bimodal latex blends containing equal weight fractions of soft and hard latex particles were investigated as a function of the particle sizes and the particle size ratio (soft particle diameter/hard particle diameter). Minimum film formation temperature (MFT) measurements were associated with transmission electron microscopy (TEM) to emphasize the particle size ratio dependence of the film formation properties. A significant increase of the MFT values with the soft/hard particle size ratio was observed. As long as the particle size ratio was low, TEM micrographs showed that the film forming soft particles, undergoing complete coalescence, clearly act as the continuous phase where the non film forming hard particles are found evenly dispersed while keeping their initial spherical shape. At higher values of the particle size ratio, TEM micrographs pointed out that the soft particles are prevented from coming into contact with each other by the surrounding hard particles, therefore dramatically increasing the MFT of the sample and resulting in a non film forming latex blend. The existence of a critical volume fraction of hard particles that is directly related to the soft/hard particle size ratio was then established on the basis of geometrical arguments involving the percolation theory. The higher the particle size ratio, the lower the critical volume fraction of hard particles that leads to a macroscopic phase inversion resulting in a non film forming bimodal latex blend. Subsequently, the mechanical film properties were investigated by solid-state dynamic mechanical analysis. The size of the dispersed hard phase was found to affect the final viscoelastic film properties. The smaller the size of the hard particles, the better the mechanical enhancement of the mechanical film properties. Last, the experimental viscoelastic thermograms were compared with some theoretical predictions based on self-consistent mechanical modeling. The final film properties of the bimodal hard/soft latex blends were then directly connected to the film formation properties.
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| 15. |
- Colombini, Didier, et al.
(författare)
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Origin of additional mechanical transitions in multicomponent polymeric materials
- 2002
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 35:15, s. 5891-5902
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Tidskriftsartikel (refereegranskat)abstract
- The viscoelastic properties of several multicomponent materials (including both particulate multipolymeric materials and multilayer polymer blends) were investigated in relation to their microstructures and phase-property dependencies. Theoretical considerations based on mechanical modeling were used to explore the origin of additional mechanical transitions in experimental viscoelastic spectra. The major part of this work was devoted to particulate multicomponent systems, and especially to the further exploration of the characteristics of the so-called micromechanical transition (MMT). Although such an additional phenomenon is clearly explained as a result of a specific interphase, our investigation also provides evidence that the occurrence of a MMT in dynamic mechanical spectra reflects the contribution of the geometrical arrangement into phases of a set of properties of the pure components, rather than a molecular relaxational process within the interfacial area. Finally, on the basis of an equivalent approach, the influence of the geometrical arrangement of phases on the viscoelastic response of multilayer polymer blends was pointed out as a relevant argument to justify the existence of "spurious" additional damping peaks in some experimental dynamic mechanical spectra reported in the literature.
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| 16. |
- Eberson, Lennart, et al.
(författare)
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Spin trapping of radicals from the reactions between donor and acceptor olefins : further evidence for the tetramethylene diradical intermediate as the initiator of spontaneous copolymerization
- 2000
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Ingår i: Macromolecules. - 0024-9297 .- 1520-5835. ; 33:6, s. 2021-2029
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Tidskriftsartikel (refereegranskat)abstract
- EPR spectroscopy and product isolation have been used to investigate the initiation of spontaneous copolymerizations of donor and acceptor monomers. The results establish the presence of tetramethylene diradicals as the only experimentally supported intermediates in the initiation for these spontaneous copolymerizations. No evidence supporting a Mayo cycloaddition mechanism, electron transfer, or charge-transfer complex initiation was found. The reaction of an olefin activated by three electron-accepting groups, such as dimethyl cyanofumarate, methyl 3,3-dicyanoacrylate, or trimethyl ethylenetricarboxylate, with a styrene having unsubstituted ortho positions was used in this study. In the presence of the spin trap 2-methyl-2-nitrosopropane (t-BuNO), aminoxyls with characteristic EPR spectra of high intensity were detected. Reaction of 4-methoxystyrene and dimethyl cyanofumarate in the presence of 2,2,6,6-tetramethylpiperidine-N-oxyl (TEMPO) led to a diamagnetic 1:1:1 adduct, 4-cyano-6-methoxy-3,4-dimethoxycarbonyl-1-piperidinyloxytetrahydronaphthalene, which was subjected to an X-ray crystallographic study. Treatment of the TEMPO adduct with t-BuNO in chloroform gave a solution containing TEMPO and the same aminoxyl as that formed from 4-methoxystyrene, dimethyl cyanofumarate, and t-BuNO. These aminoxyls were assigned the structure of spin adducts of tetrahydronaphthalen-1-yl radicals, formed by initial trapping of the diradical of the donor and acceptor olefin at the more reactive radical center, followed by cyclization into the aromatic ring. This proposed mechanism provides an alternative to the commonly accepted Mayo initiation mechanism.
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| 17. |
- Edgecombe, Samuel, et al.
(författare)
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Monte Carlo simulations of defect-free cross-linked gels in the presence of salt
- 2004
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 37:26, s. 10089-10100
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Tidskriftsartikel (refereegranskat)abstract
- Properties of polyelectrolyte gels in equilibrium with a reservoir of salt solution described within the primitive model have been investigated using Monte Carlo simulations. The polyelectrolyte gel was modeled as a charged defect-free three-dimensional network of diamondlike topology with explicit simple ions. The deswelling upon addition of salt was investigated for gels with different charge density, cross-linking density, chain flexibility, and counterion valence. All polyelectrolyte gels underwent a deswelling upon addition of salt. In most systems, however, even at high salt concentration, the equilibrium volumes remained significantly larger than those of the corresponding uncharged gels, and the salt concentration in the gel remained smaller than that in the reservoir. The salt content in the gel was larger as compared to that predicted by an ideal Donnan equilibrium due to a more negative excess chemical potential of the salt in the gel as compared to that in the reservoir. The predictions of the Flory-Rehner-Donnan theory were qualitatively in agreement with our results, but they displayed significant quantitative disagreement, mainly due to an overestimated contribution from the counterions to the osmotic pressure.
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| 18. |
- Feitosa, E, et al.
(författare)
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Interaction between poly(ethylene glycol) and C12E8 investigated by dynamic light scattering, time-resolved fluorescence quenching, and calorimetry
- 2002
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 35:1, s. 201-207
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Tidskriftsartikel (refereegranskat)abstract
- Dynamic light scattering (DLS), time-resolved fluorescence quenching (TRFQ), and isothermal titration microcalorimetry have been used to show that, in dilute solution, low molecular weight poly(ethylene glycol) (PEG, M-w = 12 kDa) interacts with the nonionic surfactant octaethylene glycol n-dodecyl monoether, C12E8, to form a complex. Whereas the relaxation time distributions for the binary C12E8/water and PEG/water systems are unimodal, in the ternary mixtures they may be either uni- or bimodal depending on the relative concentrations of the components. At low concentrations of PEG or surfactant, the components of the relaxation time distribution are unresolvable, but the distribution becomes bimodal at higher concentrations of either polymer or surfactant. For the ternary system in excess surfactant, we ascribe, on the basis of the changes in apparent hydrodynamic radii and the scattered intensities, the fast mode to a single micelle, the surface of which is associated with the polymer and the slow mode to a similar complex but containing two or three micelles per PEG chain. Titration microcalorimetry results show that the interaction between C12E8, and PEG is exothermic and about 1 kJ mol(-1) at concentrations higher than the CMC Of C12E8. The aggregation number, obtained by TRFQ, is roughly constant when either the PEG or the C12E8 concentration is increased at a given concentration of the second component, owing to the increasing amount of surfactant micelles inside the complex.
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| 19. |
- Gavelin, Patrik, et al.
(författare)
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Amphiphilic polymer gel electrolytes. 4. Ion transport and dynamics as studied by multinuclear pulsed field gradient spin-echo NMR
- 2002
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 35:13, s. 5097-5104
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Tidskriftsartikel (refereegranskat)abstract
- The transport dynamics in gel electrolytes based on amphiphilic polymers was found to be faster than in gel electrolytes based on corresponding nonamphiphilic polymers. The amphiphilic polymer studied was a polymethacrylate grafted with fluorocarbon and (EO)(9) side chains, and the nonamphiphilic one was a polymethacrylate carrying only (EO)(9) side chains. Self-diffusion coefficients of gel electrolytes based on the two polymers with different contents of 1 M lithium bis(trifluoromethylsulfonyl) imide (LiTFSI) salt in gamma-butyrolactone were determined by H-1, F-19, and Li-7 pulsed field gradient spin-echo NMR spectroscopy. The polymer self-diffusion coefficients showed that the amphiphilic polymer molecules diffused faster than the nonamphiphilic ones and seemed more intramolecularly aggregated than intermolecularly. At electrolyte contents above 43 wt %, the ion conductivity of the amphiphilic polymer gel electrolytes was higher than for the corresponding gel based on the nonamphiphilic polymer under identical conditions, as measured by impedance spectroscopy. Moreover, the lithium ion diffusion coefficient in the amphiphilic gel electrolytes was found to be significantly higher than that for corresponding gels based on the nonamphiphilic polymer, The higher ethylene oxide content of the nonamphiphilic polymer decreased the mobility of the lithium ions due to cooperative coordination of lithium ions by ether oxygens in comparison with gamma-BL. The TFSI anion diffusion was however approximately the same in the two gel systems. Consequently, the apparent lithium transference number (taudivided by) of the amphiphilic gels was higher by almost a factor of 3 as compared to that of the gels based on the nonamphiphilic polymer. A splitting of the TFSI signal in the F-19 NMR spectra suggested that the TFSI anions in the amphiphilic polymer gels were partly present in a solvent-rich environment and partly associated with the aggregates formed by the fluorinated side chains. This kind of splitting was not observed in the spectra of the gels based on the nonamphiphilic polymer. The association of TFSI anions to the aggregated fluorinated side chains may thus also play a role in increasing the value of taudivided by for the amphiphilic polymer gels.
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| 20. |
- Gillissen, S, et al.
(författare)
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Synthesis and characterization of poly(pyridine vinylene) via the sulfinyl precursor route
- 2001
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 34:21, s. 7294-7299
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis and characterization of poly(pyridine vinylene) (PPyV) via the nonionic sulfinyl precursor route is presented. Starting from an unsymmetrical monomer, precursor polymers were prepared in various solvents, which led to polymers with variable molecular weights. The thermal conversion to the conjugated structure, as well as its stability, was studied with different techniques such as FT-IR, UV-vis, TGA, and direct insertion probe mass spectroscopy (DIP-MS). From these results we were able to derive the most suitable conditions to perform the conversion. The fully conjugated PPyV was further characterized with photoluminescence (PL) and cyclic voltammetry (CV) measurements. The PL efficiency was found to be as high as 14%. The CV measurements showed that the polymer can be reduced (n-doped).
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| 21. |
- Jannasch, Patric
(författare)
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Synthesis of novel aggregating comb-shaped polyethers for use as polymer electrolytes
- 2000
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 33:23, s. 8604-8610
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Tidskriftsartikel (refereegranskat)abstract
- Polyethers having well-defined comb-shaped architectures were prepared by using poly(4-hydroxystyrene) (PHSt) as a multifunctional initiator for graft polymerization of either ethylene oxide (EO) or a mixture of EO and propylene oxide (PO). The grafting process was performed in 1,4-dioxane using NaH as ionizer for the PHSt hydroxyl groups. The precursor PHSt was prepared by first polymerizing 4-tert-butoxystyrene, using butyllithium as initiator in THF at -60 degreesC, and then deprotecting the butoxy groups. Finally, the terminal hydroxyl groups of the polyether grafts were end-capped with hexadecanoyl units through esterification. The monomer addition sequence in the graft copolymerizations with the same EO/PO feed ratio proved to have a great influence on the crystallization temperature and the crystallinity of the grafts. Also, the end-capping was found to reduce the degree of crystallinity as compared to the corresponding uncapped polymers. Solid polymer electrolytes containing lithium triflate (LiSO3-CF3) salt had ambient temperature ion conductivities of similar to 10(-5) S/cm at [Li]/[O] = 0.025. Thermal analysis of the electrolytes showed that the polymers aggregated through phase separation of the hexadecanoyl chain ends.
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| 22. |
- Johansson, DM, et al.
(författare)
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Influence of polymerization temperature on molecular weight, photoluminescence, and electroluminescence for a phenyl-substituted poly(p-phenylenevinylene)
- 2001
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Ingår i: Macromolecules. - 0024-9297 .- 1520-5835. ; 34:11, s. 3716-3719
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Tidskriftsartikel (refereegranskat)abstract
- We present the synthesis and characterization of poly(2-(2",5'-bis(2"-ethylhexyloxy)phenyl)-1,4-phenylenevinylene) (BEHP-PPV) polymerized at different temperatures. The photoluminescence efficiencies in the solid state of BEHP-PPV obtained at 144 and 0 degreesC are 28% and 60%, respectively. H-1 NMR measurements showed a lower concentration of structural defects for BEHP-PPV obtained at lower temperatures, which can explain the increased photoluminescence efficiencies for these polymers. Polymerization temperatures below 0 degreesC decrease the molecular weight without changing the photoluminescence efficiency to any large extent. The electroluminescence efficiencies follow the trend in the photoluminescence efficiencies.
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| 23. |
- Johansson, D.M., et al.
(författare)
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Synthesis and characterization of highly soluble phenyl-substituted poly(p-phenylenevinylenes)
- 2000
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 33:7, s. 2525-2529
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Tidskriftsartikel (refereegranskat)abstract
- We present the synthesis and characterization of soluble, high molecular weight phenyl-substituted poly(p-phenylenevinylenes). The studied polymers are poly(2-(2',5'-bis(2?-ethylhexyloxy)phenyl)- 1,4-phenylenevinylene) (BEHP-PPV) and copolymers of BEHP-PPV and poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV). Their photoluminescence and electroluminescence have been examined as well as their stability to air and light. The polymers emitted green and yellow light. Stability measurements showed increased stability compared to some previously known substituted PPVs.
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| 24. |
- Johansson, DM, et al.
(författare)
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Synthesis and characterization of polyfluorenes with light-emitting segments
- 2001
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Ingår i: Macromolecules. - 0024-9297 .- 1520-5835. ; 34:6, s. 1981-1986
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Tidskriftsartikel (refereegranskat)abstract
- Two new polymers consisting of poly(9-(2'-ethylhexyl)-9-hexylfluorene) (EHH-PF) with a small amount of substituted poly(p-phenylenevinylene) (PPV) segments have been synthesized and characterized. The synthetic route was designed to allow the incorporation of only one (or zero) PPV segments per polymer chain. Photoluminescence measurements showed that energy transfer from the PF segments to the more narrow band-gap PPV segments did occur, both in solution and in film. In the solid state, all emissions were detected from the PPV segments with photoluminescence quantum yields up to 68%. One of the polymers has been used as the active material in a microcavity laser device. The threshold for lasing is 2 muJ/cm(2).
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| 25. |
- Johansson, DM, et al.
(författare)
-
Synthesis of soluble phenyl-substituted poly(p-phenylenevinylenes) with a low content of structural defects
- 2002
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 35:13, s. 4997-5003
-
Tidskriftsartikel (refereegranskat)abstract
- The synthesis and characterization of two new soluble poly(p-phenylenevinylenes) (PPVs) are reported. The polymers are poly(2-2',5'-bis(octyloxy)benzene)-1,4-phenylenevinylene) (BOP-PPV) and poly(2-(2',5'-bis(octyloxy)benzene)-5-methoxy-1,4-phenylenevinylene) (BOPM-PPV). Both polymers have been polymerized at high and low temperatures to study the formation of structural defects. It is shown that both methoxy groups as side chains and low polymerization temperatures decrease the content of defects in the final polymer. As a consequence, the polymers with lower concentration of defects exhibit higher electroluminescence yields in light-emitting diodes. In addition to this, the polymers with a low content of defects exhibited longer operational lifetimes in these devices. The highest photoluminescence quantum yield in the solid state and electroluminescence efficiency were found to be 72% and 1.74%, respectively.
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| 26. |
- Jonforsen, M, et al.
(författare)
-
Synthesis and characterization of soluble and n-dopable poly(quinoxaline vinylene)s and poly(pyridopyrazine vinylene)s with relatively small band gap
- 2002
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 35:5, s. 1638-1643
-
Tidskriftsartikel (refereegranskat)abstract
- Synthesis and characterization of poly(quinoxaline vinylene)s and poly(pyridopyrazine vinylene)s with linear and branched aliphatic side chains are reported. The electron affinity of the polymers was measured with cyclic voltammetry (CV) and found to be highest for the pyridopyrazine vinylene polymers, Compared to CN-MEH-PPV, the pyridopyrazine vinylene polymers were easier to reduce, while the quinoxaline derivatives were harder. UV-vis absorption measurements showed that the polymers have relatively small band gaps.
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| 27. |
- Karlsson, G. E., et al.
(författare)
-
Determining limonene diffusion in molten polyethylene from within 0.1 mu s molecular dynamics trajectories
- 2002
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 35:19, s. 7453-7459
-
Tidskriftsartikel (refereegranskat)abstract
- Molecular dynamics simulations of the diffusion of limonene into molten polyethylene were performed in order to explore the possibility of using atomistic simulations to predict the diffusion of larger solute molecules in polymers. The system contained 6000 anisotropic united atom methylene units with a molar mass of 84 000 g mol(-1). A united atom limonene molecule (C10H16) was introduced into the polyethylene matrix. Limonene trajectories were generated for 2-100. ns at 77-227 degreesC. The simulated diffusivities were compared with experimental zero-concentration diffusivities of limonene in natural rubber and ultrahigh molar mass polyethylene, obtained from desorption measurements in the same temperature range. The simulated diffusivities and activation energy were within 30%. and 16% of the experimental thermodynamic diffusivities and activation energies, respectively. The simulated average diffusivities, obtained from 10 trajectories, changed by only 33% when the simulation time was shortened from 100 ns to 500 ps. The limonene molecule vibrated in a cagelike fashion on a 1-2 ps scale, whereas on a larger time scale the jumping was liquidlike. The limonene molecule showed tumbling during its motion through the polyethylene matrix.
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| 28. |
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| 29. |
- Loren, Niklas, et al.
(författare)
-
Phase separation induced by conformational ordering of gelatin in gelatin/maltodextrin mixtures
- 2001
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 34:2, s. 289-297
-
Tidskriftsartikel (refereegranskat)abstract
- Mixtures of gelatin and maltodextrin in aqueous solution have been quenched to temperatures at which they are initially miscible but where gelatin ordering is initiated. In many cases phase separation was observed to occur after a significant time delay, and the dependence of these delays on quench temperature and biopolymer concentration has been studied in detail using turbidity measurements and confocal laser scanning microscopy (CLSM). Furthermore, by observing the optical rotation (OR) and turbidity of the system simultaneously, the gelatin helix content and the time delay before the onset of phase separation were monitored concurrently. The observed delay times were found to correspond to the time taken for the development of a certain degree of gelatin ordering, which drives the separation process. A further consequence of gelatin ordering is the viscosifying of the solution and, at sufficient concentrations, the formation of a gel. Therefore, rheological measurements have been used in addition to turbidity measurements and CLSM in order to monitor further the structural development of the systems. A comparison of the data obtained from these techniques shows that while the development of a certain elasticity will trap the system morphology, this elasticity is not directly related to that found at the gel point. At low maltodextrin concentrations, where phase separation was not detected by turbidity, transmission electron microscopy (TEM) has been used to examine the microstructure on a smaller length scale.
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| 30. |
- Loren, Niklas, et al.
(författare)
-
Structure evolution during gelation at later stages of spinodal decomposition in gelatin/maltodextrin mixtures
- 2001
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 34:23, s. 8117-8128
-
Tidskriftsartikel (refereegranskat)abstract
- The kinetics of phase separation and gelation in kinetically trapped gelatin/maltodextrin/water gels was studied using confocal laser scanning microscopy (CLSM) and transmission electron microscopy (TEM). The time evolution of the morphology was followed by CLSM during temperature quenches from 60°C to between 1 and 40°C. The maltodextrin concentration was varied between 2.25% and 7.5% (w/w), and the gelatin concentration was held constant at 4% (w/w). Spinodal decomposition, self-similar growth, percolation-to-cluster transition, coalescence, and diffusion of maltodextrin inclusions were observed during the progress of gelation. The start and completion of these processes, the onset of phase separation, and the relative rates of phase separation and gelation were found to determine the morphology. The characteristic wavelength showed a crossover in its growth rate power law from one-third to one in a slowly gelling, near-symmetric system. Droplet and bicontinuous morphologies were observed in off-symmetric and near-symmetric quenches, respectively. Secondary phase separation occurred at low temperatures and near-symmetric composition. Partial coalescence and contracted flocculation were observed during the progress of gelation. Stereological measurements showed that the size of maltodextrin inclusions increases and that the volume fraction decreases with increasing quench temperature. In addition, the number of the maltodextrin inclusions decreases with increasing quench temperature.
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| 31. |
- Lozinsky, Vladimir I, et al.
(författare)
-
Synthesis and studies of N-vinylcaprolactam/N-vinylimidazole copolymers taht exhibit the ”proteinlike” behaviour in aquesous media
- 2003
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 36:19, s. 7308-7323
-
Tidskriftsartikel (refereegranskat)abstract
- Proteinlike copolymers were first predicted by the computer-aided biomimetic design (Physica A 1998, 249, 253-261). These copolymers consist of comonomer units of differing hydrophilicity/hydrophobicity. Heterogeneous blockiness, characteristic for such copolymers, facilitates chain folding with the formation of specific spatial packing: a dense core consisting of hydrophobic units and a polar shell formed by hydrophilic units. This paper describes the synthesis of N-vinylcaprolactam/N-vinylimidazole copolymers via the redox-initiated radical copolymerization in the medium of 10% aqueous DMSO at the temperatures both below and above the phase separation threshold. The synthesized macromolecular products were separated into thermally precipitating and nonprecipitating fractions. Their molecular weight characteristics were evaluated using size-exclusion chromatography; their comonomer composition was determined from 1H NMR spectra of copolymers dissolved in DMSO-d6. The temperature-dependent behavior of copolymer macromolecules in water was investigated by thermonephelometry, high-sensitivity differential scanning calorimetry, and 1H NMR spectroscopy of the copolymers dissolved in D2O. It was shown that thermally nonprecipitating copolymer fractions obtained at initial comonomer molar ratios of 85:15 and 90:10 can be identified as proteinlike copolymers.
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| 32. |
- Magnusson, Helene, et al.
(författare)
-
Influence of reaction conditions on degree of branching in hyperbranched aliphatic polyethers from 3-ethyl-3-(hydroxymethyl)oxetane
- 2001
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 34:17, s. 5786-5791
-
Tidskriftsartikel (refereegranskat)abstract
- The cationic ring-opening polymerization of 3-ethyl-3-(hydroxymethyl)oxetane to form hyperbranched polyethers has been studied. The polymerizations have been performed in bulk using sulfonium salt initiators. To produce polymers of different degrees of branching, the reaction conditions (reaction temperature and initiator) have been varied. Polymerizations have also been performed in the presence of a trifunctional core molecule, trimethylolpropane. The conversion of monomer turned out to be the main factor determining the degree of branching in the resulting polymer. Polymers with degrees of branching ranging from 0.15 to 0.41 were synthesized. When 3-ethyl-3-(hydroxymethyl)oxetane was polymerized by slow addition of monomer to a core molecule, a lower degree of branching was obtained compared to the one-step synthesis with full conversion of monomer. The polydispersity was generally slightly lower when a core molecule was used than in the one-step homopolymerization of 3-ethyl-3(hydroxymethyl)oxetane.
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| 33. |
- Magnusson, Heléne, et al.
(författare)
-
Structure buildup in hyperbranched polymers from 2,2-bis(hydroxymethyl)propionic acid
- 2000
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 33:8, s. 3099-3104
-
Tidskriftsartikel (refereegranskat)abstract
- The structure buildup in hyperbranched polyesters from 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) was studied experimentally. Bis-MPA and its dendritic trimer were both polymerized in bulk using acid catalyst. The fractions of terminal, dendritic, and linear repeating units were monitored by C-13 NMR during the course of reaction. Effect of slow monomer addition on the degree of branching in the final product was also studied. Hyperbranched polymers from bis-MPA with and without a core molecule were kept at the polymerization temperature in order to examine the effect of heat treatment on composition in the polymer. The fractions of the different repeating units were changing to a large extent with conversion. Slow monomer addition to a trifunctional core molecule gave a product with a degree of branching of 47%. Heat treatment of hyperbranched materials gave small changes in the fractions of the different repeating units in both materials and, eventually, gelling in the material without a core.
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| 34. |
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| 35. |
- Malkoch, Michael, et al.
(författare)
-
Dendronized aliphatic polymers by a combination of ATRP and divergent growth
- 2004
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 37:2, s. 322-329
-
Tidskriftsartikel (refereegranskat)abstract
- Dendronized, hybrid dendritic-linear polymers were synthesized by either the "graft-onto" route or by atom transfer radical polymerization (ATRP) of macromonomers. In both ways, the main chain was composed of acrylate repeating units and the dendrons were based on the aliphatic ester skeleton obtained from 2,2-bis(methylol)propionic acid (bis-MPA). ATRP of macromonomers was not a viable route for monomers with side chains larger than second-generation dendrons, which is why a combination of the two approaches was required to obtain polymers with larger side chains. The "graft-onto" route was conducted by reacting hydroxyl groups on the main chain with the acetonide-protected 2,2-bis(hydroxymethyl)propionic anhydride. The acetonide protecting group was easily removed by treating a solution of the polymer with an acidic ion-exchange resin. Dendronized polymers with 1-3 generation dendron side groups were synthesized with a maximum molecular weight of ca. 86 kDa. The products were analyzed by H-1 and C-13 NMR, SEC, and MALDI-TOF.
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| 36. |
- Malkoch, Michel, et al.
(författare)
-
Rapid and efficient synthesis of aliphatic ester dendrons and dendrimers
- 2002
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 35:22, s. 8307-8314
-
Tidskriftsartikel (refereegranskat)abstract
- A divergent approach to synthesize dendritic aliphatic polyester structures based on 2,2-bis(hydroxymethyl) propionic acid (bis-MPA) is described. The key building block is the anhydride of isopropylidene-2,2-bis(methoxy) propionic acid which is synthesized in high yields through self-dehydration, utilizing N,N'-dicyclohexylcarbodiimide (DCC) as reagent. The high reactivity of the anhydride toward hydroxyl groups makes the divergent synthesis of dendrimers and dendrons viable. Dendritic growth occurs in the presence of protecting groups sensitive toward hydrogenolysis, such as benzyl esters and ethers. The acetonide-protecting group is easily removed under acidic conditions using DOWEX 50W-X2 resin in methanol. Fourth-generation dendrons and dendrimers were successfully synthesized in high yields utilizing 1.3-1.5 equiv of anhydride per hydroxyl group. Common characteristics of the esterification reaction were short reaction time, mild reaction conditions, easy monitoring by NMR analysis, and simple workup. This synthetic approach opens up the possibility to utilize orthogonal protecting groups of acetonide-protected 2,2-bis(hydroxymethyl) propionic anhydride as a novel building block.
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| 37. |
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| 38. |
- Nilsson, Peter, et al.
(författare)
-
Enantiomeric substituents determine the chirality of luminescent conjugated polythiophenes
- 2004
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 37:17, s. 6316-6321
-
Tidskriftsartikel (refereegranskat)abstract
- Chiral isomers of 3-substituted polythiophenes with amino acid functiontionalized side chains are compared. The polymers show pH-dependent absorption, emission, and circular dichroism spectra in buffered aqueous solution. At pH equal to pI of the amino acid, the backbones adopt nonplanar helical conformations, and the polymer chains are separated from each other. Increasing pH leads to more planar conformations of the backbones and an aggregation of the polymer chains occurs. A lower pH will also lead to more planar conformation of the backbones, but aggregation of the polymer chains appears to be absent. The nonplanar to planar transition of the polymer backbone and the separation/aggregation of different polymer chains is not affected by stereochemistry of the zwitterionic side chain. The two isomers have almost identical pH-dependent absorption and emission spectra. However, the chirality of the zwitterionic side chain is reflected in the conformation of the polymer backbone, giving rise to a right-handed and left-handed helical form of polythiophene chains since the induced circular dichroism patterns of the two polymers are mirror images.
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| 39. |
- Nilsson, Peter, et al.
(författare)
-
Optical emission of a conjugated polyelectrolyte : calcium-induced conformational changes in calmodulin and calmodulin-calcineurin interactions
- 2004
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 37:24, s. 9109-9113
-
Tidskriftsartikel (refereegranskat)abstract
- Electronic polymers in aqueous media offer bioelectronic detection of biomolecular processes. Here we report fluorometric detection of calcium-induced conformational changes in calmodulin based on noncovalent assembly of calmodulin to a water-soluble zwitterionic polythiophene derivative. Assembly with calmodulin will induce a planar geometry and aggregation of the polymer chains, detected as a decrease of the intensity and a red shift of the fluorescence. Upon addition of Ca2+ the intensity of the emitted light is increased and blue-shifted. The geometrical alteration of the polymer chains can further be utilized for recording of the binding of calcineurin to the calcium-activated POWT−calmodulin complex. This novel methodology, using a conformation-sensitive probe, allows fluorometric detection of conformational changes in biomolecules and protein−protein interactions without any covalent modifications of the biomolecules. The rapid and selective method is based on noncovalent interactions between a zwitterionic polythiophene derivative and the biomolecule of interest. This offers a novel way to create microarrays without using covalent attachment of the receptor or labeling of the analyte.
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| 40. |
- Pacios, IE, et al.
(författare)
-
In situ polymerization of N,N-dimethylacrylamide in aerosol OT-water: Modified lamellar structure and multiphase separation
- 2002
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 35:20, s. 7553-7560
-
Tidskriftsartikel (refereegranskat)abstract
- N,N-Dimethylacrylamide is polymerized in the lyotropic surfactant system containing Aerosol-OT (AOT) and water. The polymerization is thermally initiated with AIBN, which allows a homogeneous initiation in this very viscous mixture. The starting mixture contains a lamellar liquid crystalline phase and an isotropic phase in equilibrium. After the polymerization, new phases develop which appear to have a lamellar structure, even if originated from the initial isotropic phase. More phases appear after the polymerization, and they are lamellar, since the phase behavior shifts toward the lamellar region when the monomer is consumed. Once the polymer is formed in situ, it segregates from the lamellae and forms an isotropic microphase which does not macroscopically separate. The appearance of this polymer-rich phase modifies the structure of the lamellar mesophase by partially deswelling it. This gives a shorter lamellar spacing. The law that expresses how the AOT-H2O spacing is contracted by the polymer is deduced from the equilibrium between the two (lamellar and isotropic) microphases. All the macroscopic final phases contain polymer, although in different proportions. The molecular weight of the polymer is the same in all phases. The presence of AOT in the medium has no influence on the resulting tacticity, which is the same as that for a polymer obtained in pure water.
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| 41. |
- Persson, Per Valdemar, et al.
(författare)
-
Selective organocatalytic ring-opening polymerization : A versatile route to carbohydrate-functionalized poly(e-caprolactenes)
- 2004
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 37:16, s. 5889-5893
-
Tidskriftsartikel (refereegranskat)abstract
- Cationic catalysis using simple carboxylic acids to combine the ring-opening polymerization of c-caprolactone and the regioselective acylation of carbohydrates has been investigated. L-Lactic acid catalyzed the acylation of methyl beta-D-glucopyranoside and sucrose with epsilon-caprolactone in high yield by bulk polymerization at 120 degreesC. The main products were regioselectively acylated on the primary hydroxyl groups of the carbohydrate end groups. The overall conversion to methyl beta-D-glucopyranoside-functionalized poly(epsilon-caprolactone) was more than 90%, M-w 2000 and polydispersity index 1.5, with one major product methyl 6-O-poly(epsilon-caprolactone)-beta-D-glucopyranoside, in agreement with the corresponding Candida antarctica lipase B-catalyzed acylation
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| 42. |
- Piletsky, SA, et al.
(författare)
-
Polymer cookery. 2. Influence of polymerization pressure and polymer swelling on the performance of molecularly imprinted polymers
- 2004
-
Ingår i: Macromolecules. - : ACS American Chemical Society. - 0024-9297 .- 1520-5835. ; 37:13, s. 5018-5022
-
Tidskriftsartikel (refereegranskat)abstract
- A set of polymers was imprinted with (+)-ephedrine at ambient and 10 bar pressure. The performance of the synthesized materials was studied by HPLC at six different temperatures: 0, 10, 20, 30, 40, and 50 degreesC. It was shown that the polymer morphology (surface area and porosity) and enantioselective properties are different for these two polymers-an unexpected result which was in contradiction with the theoretical forecasts. A possible mechanism which explains the observed phenomenon is discussed. The contributing factor which influenced the polymer performance was the polymer swelling. This shows that, in addition to temperature, other physical parameters such as pressure and polymer swelling should be analyzed and accounted for in the quality control of MIP synthesis and application.
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| 43. |
- Piletsky, SA, et al.
(författare)
-
Polymer cookery: Influence of polymerization conditions on the performance of molecularly imprinted polymers
- 2002
-
Ingår i: Macromolecules. - : ACS American Chemical Society. - 0024-9297 .- 1520-5835. ; 35:19, s. 7499-7504
-
Tidskriftsartikel (refereegranskat)abstract
- A set of polymers has been imprinted with (-)-ephedrine at six different temperatures, ranging from -30 to +80 degreesC. Polymer affinity and specificity were observed to be strongly dependent on the polymerization temperature. The experimental results suggest that the polymer is able to "memorize" the temperature used in the polymerization process in a manner similar to previously documented MIP "memory" effects for the template and polymerization solvent. In a study of the effect of temperature on retention and selectivity in HPLC (using the MIP as a column packing), a clear gradient change in the Vant Hoff plots was observed at 20-30 degreesC. This indicates a transition in binding mechanism from exothermic at higher temperatures to endothermic at lower temperatures. These results, supported by the evidence of template-induced MIP swelling, are interpreted in terms of desolvation and conformational changes in the polymers induced by the interaction with the template.
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| 44. |
- Ryner, Maria, et al.
(författare)
-
L-lactide macromonomer synthesis initiated by new cyclic tin alkoxides functionalized for brushlike structures
- 2001
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 34:21, s. 7281-7287
-
Tidskriftsartikel (refereegranskat)abstract
- L-Lactide macromonomers with an incorporated double bond were successfully synthesized by controlled ring-opening polymerization initiated by two new cyclic tin alkoxides (1,1-di-n-butyl-stanna-2,7-dioxacyclo-4-heptene and 9,9,20,20-tetrabutyl-8,10,19,21-tetraoxa-9,20-distanna-dispiro[5.5.5.5]d ocosa-2,14-diene). Initiators and crude reaction mixtures were characterized by NMR. H-1 NMR analysis showed that the initiators were completely reacted in the polymerization and that both tin-oxygen bonds were reactive and participated in propagation. The polymerizations were performed in chloroform at 60 degreesC, and the molecular weight was effectively controlled by adjusting the monomer-to-initiator ratio. The molecular weight distribution was narrow (<1.1) for both high and low molecular weights (3000-72 000 g/mol). A plot of M-n vs conversion was linear up to a conversion of 98%, showing a system propagating in a controlled manner. The kinetic investigation showed that all of the polymerizations were first order in monomer and that no termination reactions occurred during polymerization.
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| 45. |
- Ryner, M., et al.
(författare)
-
Mechanism of ring-opening polymerization of 1,5-dioxepan-2-one and L-lactide with stannous 2-ethylhexanoate. A theoretical study
- 2001
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 34:12, s. 3877-3881
-
Tidskriftsartikel (refereegranskat)abstract
- A theoretical study of the ring-opening polymerization (ROP) mechanism of 1,5-dioxepana-2-one (DXO) and (L)-lactide (LLA) with stannous(IE) a-ethylhexanoate (Sn(Oct)(2)) is presented. The B3LYP density functional method has been used for the quantum chemical calculations. Our results support a coordination-insertion mechanism initiated by a tin-alkoxide species formed prior to the ROP. The rate-determining step in the ROP was the nucleophilic attack of the alkoxide on the carbonyl carbon of the monomer. The activation energy for the ROP of DXO with Sn(Oct ')(2) has been determined to be 19.8 kcal/mol and for L-lactide 20.6 kcal/mol. At normal reaction temperatures, a ligand may dissociate as Oct 'H during propagation. An excess of carboxylic acid hinders the coordination of monomer to the initiating/propagating complex.
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| 46. |
- Schneider, Stefanie, et al.
(författare)
-
Discontinuous volume transitions in cross-linked polyelectrolyte gels induced by short-range attractions and strong electrostatic coupling
- 2004
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 37:10, s. 3850-3856
-
Tidskriftsartikel (refereegranskat)abstract
- The swelling behavior of polyelectrolyte gels with and without short-range attraction was studied at variable permittivities using Monte Carlo simulations. The primitive model, with explicit treatment of all charged species augmented with an attractive square-well potential between network particles, was used. Discontinuous volume transitions appeared at critical values of the depth of the square-well potential at fixed permittivity and at critical values of the permittivity at fixed short-range potential. In particular, we observed such a transition also without the short-range potential. The collapsed state was favored by the short-range attraction and/or at low permittivity. The volumes of the collapsed states were 1-2 orders of magnitude smaller than those of the swollen states.
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| 47. |
- Sergeyeva, TA, et al.
(författare)
-
In situ formation of porous molecularly imprinted polymer membranes
- 2003
-
Ingår i: Macromolecules. - : ACS American Chemical Society. - 0024-9297 .- 1520-5835. ; 36:19, s. 7352-7357
-
Tidskriftsartikel (refereegranskat)abstract
- Molecularly imprinted polymer membranes for a model compound, atrazine, were prepared in situ from a monomer mixture containing methacrylic acid, tri(ethylene glycol) dimethacrylate, and atrazine using U-V-initiated polymerization. To improve flexibility and mechanical stability of these membranes, oligourethane acrylate was added to the mixture of monomers. Polymeric additives were used to increase porosity of membranes and their permeability as well as to make them suited for filtration experiments. This process resulted in the formation of thin, flexible, and porous membranes containing atrazine-specific binding sites. The atrazine-imprinted membranes showed higher affinity to this herbicide than to structurally similar compounds (simazine, prometryn, and metribuzin). The binding capacity of MIP membranes was found to be significantly higher than that observed previously for MIP systems. The high affinity, specificity, and binding capacity of MIP membranes, together with their straightforward and easy preparation, provide a good basis for their application in separation and purification, e.g., in membrane chromatography.
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| 48. |
- Skepö, Marie, et al.
(författare)
-
Complexation, phase separation, and redissolution in polyelectrolyte-macroion solutions
- 2003
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 36:2, s. 508-519
-
Tidskriftsartikel (refereegranskat)abstract
- The complexation, phase separation, and redissolution of polyelectrolyte-macroion solutions have been studied by means of Monte Carlo simulations. A simple model system with focus on the electrostatic interactions has been used to examine the properties of the macroion solutions at different amounts of oppositely charged polyelectrolytes. As oppositely charged polyelectrolytes are added, the stable macroion solution with repelling macroions becomes successively less stable. The strong electrostatic attraction brings macroions and polyelectrolytes closely together, and slightly before macromolecular charge equivalence, distinct and repelling complexes formed by macroions and polyelectrolytes are established. At macromolecular charge equivalence, the system becomes unstable, and a large and loose cluster of macro ons and polyelectrolytes is formed. Finally, in excess of polyelectrolytes, the large cluster is broken up and the macroions are dispersed again-a redissolution has occurred. The effect of the macroion radius, the chain length, and the chain flexibility on the phase separation is also investigated. A semiflexible chain displayed a smaller tendency to promote phase instability as compared to flexible and stiff chains, the origin most likely arising from the similar chain persistence length and macroion radius.
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| 49. |
- Stridsberg, K., et al.
(författare)
-
Dihydroxy-terminated poly(L-lactide) obtained by controlled ring-opening polymerization : Investigation of the polymerization mechanism
- 2000
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 33:8, s. 2862-2869
-
Tidskriftsartikel (refereegranskat)abstract
- Hydroxy telechelic poly(L-lactide)s of different molecular weight have been synthesized by controlled ring-opening polymerization using cyclic tin alkoxides. NMR analysis showed that the propagation proceeded through an insertion mechanism. No free hydroxyl or carboxyl end groups were detected in the polymerization mixture. Complete reaction of the initiator was observed over the entire range of compositions studied. Both tin-oxygen bonds were reactive and participated in the propagation reaction. Peak assignments were obtained by H-1, C-13, distortionless enhancement polarization transfer (DEPT), and heteronuclear multiple quantum coherence-gradient selected (hmqc-gs) nuclear magnetic resonance spectroscopy. The kinetics of the solution polymerization of L-lactide has been investigated and showed a first order in monomer. The external order in initiator has been determined to be 3/4 for initiator concentrations above 5 mmol/L and to 2 below 2 mmol/L. The molecular weight could easily be adjusted by the monomer-to-initiator ratio, and the molecular weight distribution remained narrow even at high molecular weight(MWD < 1.15). The polymerization products were characterized by size exclusion chomatography (SEC) as well as H-1 and C-13 NMR.
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| 50. |
- Svensson, B, et al.
(författare)
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Thermotropic and lyotropic behavior of a PEO-PPO-PEO block copolymer
- 2000
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Ingår i: Macromolecules. - 0024-9297 .- 1520-5835. ; 33, s. 7413-7419
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Tidskriftsartikel (refereegranskat)abstract
- The phase behavior of the (EO)19(PO)43(EO)19/p-xylene system (where EO is ethylene oxide and PO is propylene oxide) with temperature is discussed. In this block copolymer the end blocks are crystallizable, and the middle block is noncrystallizable. Several techniques were used to delineate the phase boundaries (SAXS, WAXS, 1H NMR, 2H NMR, and DSC). An anisotropic region with a lamellar structure with semicrystalline PEO domains and amorphous PPO domains is formed at low temperatures and high copolymer concentrations. The lamellar structure has a one-dimensional swelling with increasing p-xylene concentration. The driving force for forming the anisotropic region is that the PEO crystallize at low temperatures. The amount of crystallinity in the system and the interfacial area per PEO block in the ordered region depend on the temperature and the sample composition. At high temperatures and low copolymer concentrations the system contains an isotopic solution phase
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