| 1. |
- Andersson, Mats R., et al.
(författare)
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Electroluminescence from Substituted Poly(thiophenes) : From Blue to Near-Infrared
- 1995
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Ingår i: Macromolecules. - : American Chemical Society. - 0024-9297 .- 1520-5835. ; 28:22, s. 7525-7529
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Tidskriftsartikel (refereegranskat)abstract
- We report a systematic approach to the control of the conjugation length along the poly(thiophene) backbone. The planarity of the main chain can be permanently modified by altering the pattern of substitution and character of the substituents on the poly(thiophene) chain, and the conjugation length is thus modified. We obtain blue, green, orange, red, and near-infrared electroluminescence from four chemically distinct poly(thiophenes). The external quantum efficiencies are in the range of 0.01-0.6%.
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| 2. |
- Andersson, S. Peter, et al.
(författare)
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Relaxation Studies of Poly(propylene glycol) under High Pressure
- 1998
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 31:9, s. 2999-3006
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Tidskriftsartikel (refereegranskat)abstract
- The effect of pressure on the relaxation processes in poly(propylene glycol) of number-average molecular weights 400 and 4000 g mol-1 (PPG-400 and PPG-4000) has been investigated using dielectric spectroscopy as well as thermal conductivity and heat capacity measurements. The relaxations associated with segmental motions within the polymer chain (α relaxation) and whole chain motions (α' relaxation) have been studied in the temperature range 200-400 K for pressures up to 2 GPa. The two processes display slightly different sensitivities to pressure, and as a consequence, are better separated at high pressures. As a result, high-pressure data exhibit the α' relaxation also in PPG-400, whereas previous investigations at atmospheric pressure have detected it only in PPG of molecular weights above about 1000 g mol-1. At atmospheric pressure, the values for (∂T/∂p)τ=1s of the alpha relaxation are, respectively, 140 and 192 K GPa-1 for PPG-400 and PPG-4000, where τ is the relaxation time. Because of the difference in (∂T/∂p)τ, the relaxation of the α motions and therefore the glass-transition temperature exhibits a more significant dependence on molecular weight at high pressures. At 295 K and 0.3 GPa, the activation volumes for the α and α' processes of PPG-4000 are about the same (approximate to 45 cm3 mol-1). At the same conditions, the activation volume for the α process of PPG-400 is about half of that for PPG-4000. An analysis of the α relaxation in terms of the strong-fragility classification shows that the degree of fragility of both PPG-400 and PPG-4000 increases slightly with increasing pressure.
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| 3. |
- Bergfeldt, K, et al.
(författare)
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Phase Separation Phenomena and Viscosity Enhancements in
- 1995
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 28:9, s. 3360-3370
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Tidskriftsartikel (refereegranskat)abstract
- Interactions between poly(styrenesu1fonate) (PSS) and poly(acry1ic acid) (PA) in aqueous solution have been studied, with and without added salt, and at various degrees of neutralization (a) of PA. Equilibrium phase diagrams have been determined, and the viscosities of monophasic mixtures have been measured. Both types of experiments reveal striking effects of a on the PA-PSS interactions. Salt-free mixtures with fully or partially neutralized poly(acry1ic acid) phase separate segregatively, except at very low a where, instead, an association between PA and PSS occurs. The association is evidenced by a dramatically increased viscosity, relative to solutions of PA or PSS alone, in semidilute mixtures. Addition of salt (1 M NaC1) results in an increased two-phase area at all a, and in the appearance of an associative phase separation for non-neutralized PA. The qualitative phase behavior observed in the presence of salt can be generated by calculations using the Flory-Huggins theory, if it is assumed that both the PSS-PA and the PA-solvent interactions change monotonically with a in a specified fashion. All experimental observations, and the theoretical modeling, suggest that the effective PA-PSS interaction changes (over a narrow interval of a) from an attraction at very low a to a repulsion at higher a.
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| 4. |
- Björling, Mikael, et al.
(författare)
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An NMR Self-Diffusion Study of the Interaction between Sodium Hyaluronate and Tetradecyltrimethylammonium Bromide
- 1995
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 28:20, s. 6970-6975
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Tidskriftsartikel (refereegranskat)abstract
- A decrease of the NMR self-diffusion coefficient of sodium hyaluronate (NaHy) upon increasing tetradecyltrimethylammonium bromide (TTAB) concentration in 202 mM NaCl (just enough to attain single phase conditions irrespective of the TTAB concentration) is interpreted in terms of the formation of NaHy–TTAB complexes containing several NaHy chains. The complexes are judged to be induced by multiple-site electrostatic condensation of TTAB micelles onto the Hy chains. Thus, the TTAB micelles may act as bridging points between, and within, the NaHy chains. For a 1% wt NaHy solution, at 202 mM NaCl, the fraction of adsorbed TTAB has a maximum at 10 mM TTAB where an estimated 54% of all the added TTAB is bound. At 70 mM TTAB, the fraction of bound TTAB has decreased to 42%. The decrease of the binding constant with increasing TTAB concentration is attributed to a more efficient electrostatic screening; i.e., the ionic strength (due to uncondensed species) increases. The observed NaHy–TTAB complexes are likely to be precursors of the precipitated phase formed at lower salt concentrations.
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| 5. |
- Björling, Mikael
(författare)
-
Using end-confined chains to model end-absorbing, triblock copolymers : 1. Analytical approach
- 1998
-
Ingår i: Macromolecules. - 0024-9297 .- 1520-5835. ; 31:25, s. 9026-9032
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Tidskriftsartikel (refereegranskat)abstract
- The bridging attraction, mediated by associative, triblock copolymers with insoluble end blocks and a soluble spacer block, is analyzed using scaling arguments and analytical methods. Adsorbing these associative polymers (APs) onto a single surface, the approach of another, bare, surface results in a strong bridging attraction. When both slit surfaces bear adsorbed APs, the bridging attraction is much weaker. The main contribution is an entropic gain since bridge formation decreases the monomer number density in the crowded region near the surface.
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| 6. |
- Björling, Mikael, et al.
(författare)
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Using end-confined chains to model end-absorbing, triblock copolymers : 2. Numerical approach
- 1998
-
Ingår i: Macromolecules. - 0024-9297 .- 1520-5835. ; 31:25, s. 9033-9043
-
Tidskriftsartikel (refereegranskat)abstract
- The bridging attraction mediated by end-absorbing, triblock copolymers in a good solvent is analyzed using numerical methods and compared to analytical results. Good agreement is found. The main deviations may be attributed to the neglect of thermal fluctuations in the extension of the loops at the brush edge in the analytical treatment. With a suitable choice of "natural" units, the numerical results for the bridging probability and the free energy of interaction per chain collapse onto universal master curves in the two arrangements considered: symmetric and asymmetric adsorption of associative polymers (APs) on the surfaces of a planar slit.
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| 7. |
- Edman, Ludvig, 1967-, et al.
(författare)
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Effect of C60 as a Filler on the Morphology of Polymer−Salt Complexes Based on Poly(ethylene oxide) and LiCF3SO3
- 1999
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 32:12, s. 4130-4133
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Tidskriftsartikel (refereegranskat)abstract
- The inclusion of C60 as a filler in complexes of paly(ethylene oxide) (PEO) and LiCF3SO3 salt reduces the degree of crystallinity of the material at ambient temperature. The observed effects are manifested as changes in characteristic vibrational modes of the crystalline polymer in FT-Raman spectra over a range of temperatures. The introduction of relatively small amounts of C60 also stabilizes ionic substructures present in these systems. Interestingly, no internal modes of the C60 molecule are affected by dissolution in PEO or by the presence of varying amounts of LiCF3SO3 salt in the matrix. From the absence of a shift in the C60:s charge-transfer-sensitive Ag(2) mode, in particular, it appears as though C60 essentially acts as an inert filler in these complexes.
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| 8. |
- Eklind, H, et al.
(författare)
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Characterization of the interphase in PPO/PMMA blends compatibilized by P(S-g-EO)
- 1996
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 29:3, s. 984-992
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Tidskriftsartikel (refereegranskat)abstract
- The influence of a poly(styrene-graft-ethylene oxide) (P(S-g-EO)) copolymer on poly(2,6-dimethyl-p-phenylene oxide)/poly(methyl methacrylate) (PPO/PMMA) blends was studied by a number of different techniques in order to characterize the properties of the interphase. Scanning electron microscopy shows that the copolymer reduces the dispersed phase size, and dynamic mechanical spectroscopy (DMS) reveals a new micromechanical transition in the ternary blends. These effects are shown to be caused by a copolymer-rich interphase with a certain volume fraction and with its own characteristic properties. Solid-state nuclear magnetic resonance (NMR) relaxation times indicate that the poly(ethylene oxide) side chains of the copolymer are partially miscible with PMMA in the ternary blends, which suggests that the interphase does not only consist of pure copolymer.
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| 9. |
- Eskilsson, K, et al.
(författare)
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Equilibrium and kinetic features of triblock copolymers at hydrophobic surfaces
- 1997
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Ingår i: Macromolecules. - 0024-9297 .- 1520-5835. ; 30, s. 6323-6332
-
Tidskriftsartikel (refereegranskat)abstract
- The adsorption of a series of (ethylene oxide-tetrahydrofuran-ethylene oxide), EOn/2THFmEOn/2, triblock copolymers has been studied at the water/hydrophobic silica interface by time-resolved ellipsometry. The copolymers form monolayers with the middle tetrahydrofuran block anchoring at the surface and the ethylene oxide groups either anchoring at the surface or protruding into the aqueous phase. The degree of anchoring of the EO chains depends critically on the surface coverage. The copolymer isotherms are generally rather well described by the conventional Langmuir expression, and the plateau surface area per polymer molecule increases linearly with the molecular weight. However, the plateau thickness exhibits a more complex behavior. At low coverages, the adsorbed layer thickness is small, and both THF and EO chains form trains at the surface. As the surface coverage increases, however, the EO chains are increasingly forced away from the surface, and the mean thickness of the adsorbed layer exhibits a relatively strong linear dependence on the surface excess. At higher coverages, closer to the adsorption plateau, a weaker dependence is observed. The thickness increase is in this latter region due to the increasing steric repulsion between protruding EO chains. Outside the adsorbed layer, we also found support for the existence of a depletion layer. We show further that there are three regimes in the kinetics of adsorption. In the first (low surface coverage), the process is diffusion controlled and the rate is proportional to the concentration difference between the bulk solution and the subsurface located just outside the adsorbed layer. In the second regime (intermediate coverages and adsorption times), the kinetics are governed by the rate of displacement of anchored EO chains by THF chains of adsorbing copolymers. In the third regime (high surface coverages), the adsorption slows down markedly due to the energy barrier caused by presence of the relatively dense brush of adsorbed EO chains. In this regime, the surface excess varies proportionally with log t, which was also observed to be the case during the desorption process.
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| 10. |
- Eskilsson, K, et al.
(författare)
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Interfacial behaviour of triblock copolymers at hydrophilic surfaces
- 1998
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Ingår i: Macromolecules. - 0024-9297 .- 1520-5835. ; 31, s. 5075-5083
-
Tidskriftsartikel (refereegranskat)abstract
- We report on the adsorption of a series of poly(ethylene oxide)-polytetrahydrofuran-poly(ethylene oxide) copolymers, EOn/2THFmEOn/2, at hydrophilic silica surfaces and relate our findings to the corresponding behavior at hydrophobic surfaces. The adsorption of these copolymers is similar to that of poly(ethylene oxide) homopolymers at low bulk concentrations. However, the copolymer adsorption increases strongly above a certain threshold concentration. This increase, which begins more than 1 order of magnitude below the critical micellar concentration (cmc), is related to the concomitant formation of micellar-like structures at the hydrophilic surfaces. We show in this work that a commercial (ethylene oxide-propylene oxide-ethylene oxide) triblock copolymer, Pluronic F127, exhibits a similar behavior at silica. Due to surface aggregation, much thicker layers are measured on silica than at the hydrophobic surface, where the adsorption results in the formation of a monolayer structure. The adsorbed amount and layer thickness measured on bare silica tend to decrease when the bulk concentration is raised above the cmc. We infer that this is due to changes of the molecular weight distribution and relative block sizes of the copolymers in the surface aggregates, i.e., a polydispersity effect. This study also covers some aspects of the adsorption and desorption kinetics exhibited by the copolymers at silica. As is common for adsorbing polymers, the concentration dependent adsorption process is generally observed to be much faster than the desorption process. The adsorption process is in parts diffusion controlled but overall to a complex to be fully analyzed. During adsorption from solutions with bulk concentrations exceeding the cmc, a clear overshoot of the surface excess is observed after intermediate adsorption times. Again, this is interpreted as being due to polydispersity. Finally, after an initial rapid desorption regime, the surface excess exhibits a logarithmic decay with time during desorption.
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| 11. |
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| 12. |
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| 13. |
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| 14. |
- Jannasch, Patric
(författare)
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Surface structure and dynamics of block and graft copolymers having fluorinated poly(ethylene oxide) chain ends
- 1998
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 31:4, s. 1341-1347
-
Tidskriftsartikel (refereegranskat)abstract
- The surface compositions of poly(styrene-b-ethylene oxide) and poly(styrene-g-ethylene oxide) films were found to be largely determined by the nature of the poly(ethylene oxide) (PEO) chain ends. Angle-dependent X-ray photoelectron spectroscopy revealed that polystyrene (PS) dominated the surfaces of the copolymers having PEO chain ends terminated by hydroxyl groups (SEO). Also, the PEO content decreased with decreasing sampling depth. In contrast, the surface regions of the corresponding copolymers having fluorinated PEO chain ends (fSEO) were dominated by PEO, and the PEO content increased with decreasing sampling depth. The fluorine content of fSEO also increased with decreasing sampling depth, indicating that the fluorinated chain ends were segregated at the outermost surface. The studied fSEO block copolymer seemed to have a higher surface concentration of fluorinated chain ends than the fSEO graft copolymers. Although it is likely that the fSEO surfaces were fully covered by fluorinated chain ends, the advancing water contact angles on fSEO films were markedly lower than on the corresponding SEO films. Moreover, low contact angles were retained even after prolonged annealing of the fSEO films in a vacuum. The surface behavior of BEO may be explained by the presence of flexible, fluorinated PEO chain ends, providing a highly dynamic surface. When fSEO films are immersed in water, the surfaces can rapidly restructure and expose PEO.
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| 15. |
- Karlsson, Sigbritt, et al.
(författare)
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Dicarboxylic acids and ketoacids formed in degradable polyethylenes by zip depolymerisation through a cyclic transition state
- 1997
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Ingår i: Macromolecules. - 0024-9297 .- 1520-5835. ; 30, s. 7721-7728
-
Tidskriftsartikel (refereegranskat)abstract
- The intermediate and final degradation products formed in six different low-density polyethylene (LDPE) films modified with either starch and/or pro-oxidants or photosensitizers (Scott-Gilead formulation [SG]) were investigated. We propose that dicarboxylic acids and ketoacids, formed in the materials to varying degrees, are due to both secondary oxidation products and a zip depolymerization mechanism by backbiting through a cyclic transition state. Hydrocarbons, ketones, carboxylic acids and dicarboxylic acids are formed during early stages of photo-oxidation, and the ketones disappeared while several ketoacids appeared and the relative amount of dicarboxylic acids increased in the most severely degraded materials. During prolonged photo-oxidation, additional oxidation of ketones and monocarboxylic acids to dicarboxylic acids explains the high amount of dicarboxylic acids. In the thermooxidized samples the amount of ketones and monocarboxylic acids remained high even in the most degraded samples. Mono-and dicarboxylic acids were formed in several micrograms per 100 mg of polymer, while the ketones and ketoacids were formed in fewer micrograms per 100 mg of polymer. LDPE modified with the iron dimethyldithiocarbamate (SG1) was the most susceptible material to photooxidation, while LDPE containing starch and pro-oxidants (LDPE-MB) was the most susceptible material to thermo-oxidation. Degraded LDPE-MB demonstrated less formation of degradation products; e.g., only in UV-initiated samples thermally degraded at 80 degrees C for 5 weeks could degradation products be detected. Larger amounts of ketones and ketoacids were formed in the SG materials than in the starch-filled materials.
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| 16. |
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| 17. |
- MALMSTROM, E, et al.
(författare)
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HYPERBRANCHED ALIPHATIC POLYESTERS
- 1995
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 28, s. 1698-1703
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Tidskriftsartikel (refereegranskat)abstract
- Hyperbranched, aliphatic polyesters of theoretically calculated molar masses 1200-44 300 were synthesized in the molten state from 2,2-bis(hydroxymethyl)propionic acid (repeating unit of AB(x) type) and 2-ethyl-2-(hydroxymethyl)-1,3-propanediol (core molecule) using acid catalysis. The synthesis procedure was a pseudo-one-step reaction where stoichiometric amounts corresponding to each generation were added successively. The resulting polymers were glassy, slightly yellow solids at room temperature with hydroxyl groups as terminal groups. The degree of branching of the polyesters was determined with the help of model compounds using C-13-NMR and was found to be near 80%. The material exhibited good thermal stability as analyzed with TGA in a nitrogen atmosphere. Glass transition temperatures were determined using DSC and were found to be about 40 degrees C and to be relatively insensitive to variations in molar mass.
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| 18. |
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| 19. |
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| 20. |
- Svensson, Mårten, et al.
(författare)
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Phase Behavior in Aqueous Two-Phase Systems Containing
- 1995
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 28:10, s. 3597-3603
-
Tidskriftsartikel (refereegranskat)abstract
- The phase behavior of the three-component PEO-PPO-PEO/dextradwater system has been studied. Pluronic L64, P105, and F68 were used, and they are members of a family of triblock copolymers with the structure PEO-PPO-PEO, where PEO is poly(ethy1ene oxide) and PPO poly- (propylene oxide). Moreover, these triblock copolymers tend to self-aggregate in aqueous solution at increasing temperature. The phase behavior of the three-component system was studied both experi- mentally and theoretically at different temperatures corresponding to the unimer (monomolecular) and the micellar region of the PEO-PPO-PEO polymers. The determination of the unimer and micellar regions was performed with a dye solubilization technique using 1,6-diphenyl-1,3,5-hexatriene (DPH) as a spectroscopic probe. A strong temperature effect on the phase behavior in PEO-PPO-PEO/dextrad water systems was observed in the case of Pluronic L64 and P105. At elevated temperature (40 "C) the micellization of the PEO-PPO-PEO polymers leads to a drastic change of the tie-line slopes as well as the shape of the binodals. Qualitative agreements were found between experimental findings and theoretical calculations using a Flory-Huggins lattice theory extended with internal degrees of freedom by modeling the PEO-PPO-PEO polymers as a poly(ethy1ene oxide) chain. This supports the prevailing picture that the more hydrophobic PPO block is shielded from water contacts by forming hydrophobic domains surrounded by EO segments.
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| 21. |
- Ullner, Magnus, et al.
(författare)
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A Monte Carlo Study of Titrating Polyelectrolytes in the Presence of Salt
- 1996
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Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 29:20, s. 6645-6655
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Tidskriftsartikel (refereegranskat)abstract
- Monte Carlo simulations have been performed for two simple models of a titrating polyelectrolyte: (i) a rigid rod and (ii) a freely jointed chain. Both models have fixed bond lengths, and the polyelectrolyte charges interact through a screened Coulomb potential. Chains consisting of 80-1000 monomeric units have been studied at three salt concentrations: 0.001, 0.01, and 0.1 M. Conformational properties and the apparent dissociation constant are reported as functions of chain length, chain ionization, monomer-monomer bond length, and salt concentration. Mean field expressions are compared to the simulation results and are, in general, found to be excellent approximations for the rigid rod, but they are also able to provide semiquantitative descriptions of the apparent dissociation constant for the freely jointed chain. Comparisons with experimental data show that the conformational properties of the flexible model can reproduce features of the titration curves, although the use of a screened Coulomb potential overestimates the response to changes in salt concentration.
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| 22. |
- Wastlund, C., et al.
(författare)
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Miscibility of styrene-maleic anhydride and styrene-acrylonitrile blends studied by positron annihilation lifetime spectroscopy
- 1998
-
Ingår i: Macromolecules. - 0024-9297 .- 1520-5835. ; 31:10, s. 3322-3327
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Tidskriftsartikel (refereegranskat)abstract
- Blends of melt-mixed styrene - maleic anhydride and styrene - acrylonitrile copolymers were examined with respect to miscibility and free volume parameters. Differential scanning calorimetry, dynamic mechanical analysis, scanning electron microscopy, and positron annihilation lifetime spectroscopy were used to judge blend miscibility. It was found that blends containing copolymers with similar amounts of styrene were miscible. Positron annihilation lifetime spectra of all blends were evaluated with the POSITRONFIT and the MELT program, where the latter can be used to obtain lifetime distributions. The mean o-Ps lifetimes (or hole sizes) of the blends were found always to be between those of the pure constituents. Pronounced negative deviations of the o-Ps intensity from weighted averages were measured in miscible blends but not in immiscible ones. Immiscible blends exhibit, on the basis of MELT evaluations, unsymmetric and broader o-Ps lifetime distributions than do miscible blends.
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| 23. |
- Wieczorek, W., et al.
(författare)
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Polyether, Poly(N,N-dimethylacrylamide), and LiClO4 Composite Polymeric Electrolytes
- 1996
-
Ingår i: Macromolecules. - : American Chemical Society (ACS). - 0024-9297 .- 1520-5835. ; 29:1, s. 143-155
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Tidskriftsartikel (refereegranskat)abstract
- The results of detailed studies of the ionic conductivity, ultrastructure, and morpholgy of polyether-poly(N,N-dimethylacrylamide) electrolytes are presented and discussed. These composite electrolytes have been studied using differential scanning calorimetry (-110-150 degrees C), with FT-IR spectroscopy (20-85 degrees C) and impedance analysis (-20-100 degrees C): Room temperature FT-Raman spectroscopy, SEM, and X-ray energy dispersive studies have also been performed. Highly crystalline poly(ethylene oxide) and amorphous or low-crystalline oxymethylene-linked poly(ethylene oxide) are used as polyether matrices for composite electrolytes. It is shown that interactions of lithium cations with polyether oxygens and the carbonyl oxygens of the ''filler'' poly(N,N-dimethylacrylamide) lead to the formation of various types of complexes. These interactions can be classified as Lewis acid-base reactions. The formation of different types of complexes modifies the ultrastructure and enhances the subambient and ambient temperature ionic conductivity of these electrolytes in comparison to the pure polyether-LiClO4 electrolyte. The increase in the conductivity is attributed to the presence of a highly flexible uncomplexed polyether phase surrounding filler particles. The temperature dependence of ionic conductivity is Arrhenius at ambient and subambient temperatures and VTF at higher temperatures. The order-disorder transition temperature calculated on the basis of a semiempirical model is found to be equal to the onset temperature of the melting peak of the crystalline poly(ethylene oxide) for these semicrystalline electrolytes or equal to 1.2 times the glass transition temperature of the polyether-LiClO4 electrolyte for the corresponding amorphous systems. Assuming that the enhanced conductivity of these composite polymer electrolytes is associated with interphase phenomena, the conductivity results were analyzed in terms of a model based on effective medium theory.
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| 24. |
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| 25. |
- Dérand, Helene, et al.
(författare)
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Pol(ethylene glycol) Graft Copolymers Containing Carboxylic Acid Groups: Aggregation and Viscometric Properties in Aqueous Solution
- 1996
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Ingår i: Macromolecules. - 0024-9297. ; 29:27, s. 8770-8775
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Tidskriftsartikel (refereegranskat)abstract
- Poly(ethylene glycol) monomethyl ethers (MPEG) were grafted on copolymers of maleic anhydride and styrene, methyl methacrylate, and ethylhexyl methacrylate, respectively. Hydrolysis of the remaining anhydride residues gave graft copolymers carrying a large number of carboxylic acid groups along the main chains. The properties in aqueous solutions of these graft copolymers were studied with respect to aggregation behavior and viscometric properties, Aggregation of the polymers was examined by quasi-elastic light scattering and now field-flow fractionation in water and KCl solution. Both methods showed that the anionic graft copolymers mainly were present as single molecules in pure water, with a minor fraction of aggregates. In KCI solution, aggregates with average sizes of approximately 30 nm were the dominant species. In aqueous solution, the polymers exhibited polyelectrolyte behavior, i.e., a dramatic increase of the viscosity upon neutralization. Graft copolymers with hydrophobic groups in the backbone had lower viscosities.
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| 26. |
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| 27. |
- FLOUDAS, G, et al.
(författare)
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DYNAMICS OF THE STRONG POLYMER OF N-LAURYL METHACRYLATE BELOW AND ABOVE THE GLASS-TRANSITION
- 1995
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Ingår i: MACROMOLECULES. - : AMER CHEMICAL SOC. - 0024-9297. ; 28:20, s. 6799-6807
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Dielectric spectroscopy (DS) and dynamic light scattering (DLS) are employed to study the dynamics of poly(n-lauryl methacrylate) (PnLMA) (M(w) 1.1 x 10(5)) at temperatures below and above the glass transition temperature T-g (T-g approximate to 225 K). T
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| 28. |
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| 29. |
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| 30. |
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| 31. |
- KONAK, C, et al.
(författare)
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PHASE-SEPARATION IN CONCENTRATED-SOLUTIONS OF 2 HOMOPOLYMERS AND A DIBLOCK COPOLYMER
- 1995
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Ingår i: MACROMOLECULES. - : AMER CHEMICAL SOC. - 0024-9297. ; 28:8, s. 2852-2857
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The dynamic behavior of polystyrene (PS) (M(W) = 9.0 x 10(5)), poly(methyl methacrylate) (PMMA) (M(W) = 1.4 x 10(6) or 1.0 x 10(5)), and styrene-methyl methacrylate diblock copolymer (S-b-MMA) (M(W) = 8.0 x 10(4)) mixtures in a solvent isorefractive with
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| 32. |
- Lauenstein, A, et al.
(författare)
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Water absorption by polymer electrolytes studied by NMR imaging
- 1998
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Ingår i: MACROMOLECULES. - : AMER CHEMICAL SOC. - 0024-9297. ; 31:12, s. 3886-3894
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Water diffusion into the polymer electrolytes (Pb, Zn)(CF3SO3)(2)(PEO)(n) leads to a dramatic increase of the ionic conductivity. Magnetic resonance imaging, MRI, has been used to study this water diffusion by one-dimensional mapping of properties such as
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| 33. |
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| 34. |
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| 35. |
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| 36. |
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| 37. |
- Porsch, B, et al.
(författare)
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Association of ethyl(hydroxyethyl)cellulose solutions
- 1997
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Ingår i: MACROMOLECULES. - : AMER CHEMICAL SOC. - 0024-9297. ; 30:16, s. 4626-4632
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Ethyl(hydroxyethyl)cellulose (EHEC) forms true molecular solutions in 10 mM aqueous solution NaCl at concentrations equal or less than 0.1%. Less hydrophilic EHEC forms true molecular solution also in methanol/10 mM aqueous NaCl(1:I, v/v) mixture. An asso
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| 38. |
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| 39. |
- Stepanek, P, et al.
(författare)
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Multiple relaxations of concentration fluctuations in entangled polymer solutions
- 1998
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Ingår i: MACROMOLECULES. - : AMER CHEMICAL SOC. - 0024-9297. ; 31:6, s. 1889-1897
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We have investigated by dynamic light scattering the dynamics of semidilute polymer solutions in a good solvent, specifically polystyrene in benzene. We have shown that, using state-of-the-art instrumentation and data analysis techniques, it is possible t
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| 40. |
- Stepanek, P, et al.
(författare)
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Relaxation of concentration fluctuations in a shear field
- 1996
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Ingår i: MACROMOLECULES. - : AMER CHEMICAL SOC. - 0024-9297. ; 29:27, s. 8888-8893
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- We have investigated relaxations in a semidilute solution of a high molecular weight polystyrene in the vicinity of Theta conditions, using three different techniques: dynamic light scattering, relaxation of flow after cessation of shear recorded through
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