| 1. |
- Alla, Abdelilah, et al.
(författare)
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Acylated and hydroxylated polyamides derived from L-tartaric acid
- 2005
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Ingår i: Polymer. - : Elsevier. - 0032-3861 .- 1873-2291. ; 46:9, s. 2854-2861
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Tidskriftsartikel (refereegranskat)abstract
- A series of polyamides 6,4 were prepared from 1,6-hexanediamine and active esters of 2,3-di-O-acylated l-tartaric acid by polycondensation in solution. Both O-alkoyl and O-benzoyl esters were used as hydroxyl protecting groups. The resulting acylated polytartaramides were found to be semicrystalline polymers with Tm between 100 and 200°C and Tg slightly above 100°C. Controlled hydrolysis of the ester side group led to the preparation of poly(hexamethylene l-tartaramide)s with different content in free hydroxyl groups. These polyamides continue being crystalline but their properties largely differ from those displayed by their parent acylated polymers.
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| 2. |
- Courtois, Julien, et al.
(författare)
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Novel monolithic materials using poly(ethylene glycol) as porogen for protein separation
- 2006
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Ingår i: Polymer. - Guildford, Surrey : Butterworth. - 0032-3861 .- 1873-2291. ; 47:8, s. 2603-2611
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Tidskriftsartikel (refereegranskat)abstract
- Several recipes are described for the preparation of porous polymeric monoliths in the capillary format, using poly(ethylene glycol) (PEG) as porogen as well as constituent in the monomer mixture. Acrylic or methacrylic monomers with a variety of terminal groups, with and without ethylene glycol links of differing lengths in the side chains, have been used in combination with triethylene glycol dimethacrylate (TEGDMA) and trimethylol-propane trimethacrylate (TRIM) as cross-linkers. PEGs of 4–20 kDa molecular weight dissolved in 2-methoxy-ethanol were used as porogens to yield large, biocompatible pores. A number of common solvents have been used as co-porogens for the PEGs, and the surface areas, median pore diameters, and back pressures of the resulting monoliths have been correlated with a number of molecular descriptors by means of chemometrics to describe the results. Photopolymerizations induced by either continuous or pulsed UV light were furthermore compared. Pore size distribution and surface area characterization have been assessed by nitrogen adsorption–desorption and mercury intrusion porosimetry, and scanning electron microscopy (SEM) was used to evaluate the differences in macroporous morphology obtained with the different porogen solutions. Mixtures selected from screening syntheses carried out in vials have been implemented in 100 μm fused silica capillaries and the back pressures measured and cross-validated with the pore information. Some of these capillary columns were finally tested for the separation of proteins using micro-HPLC.
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| 3. |
- Gasslander, Ulla, et al.
(författare)
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Polymer-water partition coefficients of extended range measured by using organic modifiers in the aqueous phase
- 2007
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861 .- 1873-2291. ; 48:26, s. 7523-7530
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Tidskriftsartikel (refereegranskat)abstract
- A procedure for estimating equilibrium polymer-water partition coefficients over a broad range of solute hydrophobicity is presented and evaluated. The coefficients were calculated from the concentration change in the liquid phase and hydro-organic mixtures of varying proportions were used to extend the range. Three hydrophobic polymers (PP, PE, and EBA), two types of solvent (acetonitrile and alcohols) and 12 model solutes were used. The estimated polymer-water partition coefficients, log K-pw, ranged from -0.5 to 8.5. The coefficients correlated to other partitioning systems such as the calculated log Poctanol-water up to similar to 14 and the retention factor (log k(w)) in reversed-phase liquid chromatography.
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| 4. |
- Gelin, Kristina, et al.
(författare)
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Characterization of water in bacterial cellulose using dielectric spectroscopy and electron microscopy
- 2007
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861 .- 1873-2291. ; 48:26, s. 7623-7631
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Tidskriftsartikel (refereegranskat)abstract
- It is shown that only 10% of the 99 wt% water present in bacterial cellulose (BC) gels, produced by Acetobacter xylinum, behave like free bulk water; the majority of the water molecules in the gels is more or less tightly bound to the cellulose. The magnitude of the diffusion coefficients of ions transported in the water phase of the BC gels as well as the information contained in freeze fracture transmission electron microscopic images of the gel structures indicates that the bulk-like water is confined in “lakes” rather than forming a continuous phase throughout the gel. Water desorption isotherms suggest that these “lakes” decrease in size with increasing oxygen concentration used during the biosynthesis process of the gels.
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| 5. |
- Johansson, Erik, et al.
(författare)
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Molecular simulation of the effect of ionic impurities and external electric fields on rod-like water clusters in polyethylene
- 2008
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Ingår i: Polymer. - : Elsevier Ltd. - 0032-3861 .- 1873-2291. ; 49:24, s. 5357-5362
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Tidskriftsartikel (refereegranskat)abstract
- Monte Carlo methods have been combined with end-bridging methods to study the solubility and structure of water in polyethylene, where the polyethylene contains a pair of oppositely charged ionic impurities. The water in the polymer is in equilibrium with pure liquid water. Both the polymer and pure water phases are exposed to an external electric field. The ions dramatically increase the solubility of water in polyethylene and induce the formation of a stable, rod-like water cluster between the ions. The solubility, the hydrogen-bond ordering of the water molecules in the cluster and the size of the cluster increase in the presence of an external field that enhances the local electric field between the ions. When the direction of the external field is reversed, and when it has the same magnitude as the local ionic field, the rod-like structure is broken up and a smaller cluster forms around each ion. (C) 2008 Elsevier Ltd. All rights reserved.
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| 6. |
- Jonsson, Magnus, 1973-, et al.
(författare)
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Suspension polymerization of thermally expandable core/shell particles
- 2006
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Ingår i: Polymer. - Amsterdam : Elsevier Ltd.. - 0032-3861 .- 1873-2291. ; 47:10, s. 3315-3324
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Tidskriftsartikel (refereegranskat)abstract
- Acrylonitrile (AN)-methacrylonitrile (MAN) copolymer particles with a core/shell structure were prepared by suspension polymerization. The particles were about 10–20 μm in diameter and had a hollow core containing an inert hydrocarbon. The influence of the monomer feed ratio and the polymerization temperature on the particle morphology was studied. One purpose of this study was to determine the boundaries for achieving a core/shell structure with the polymer encapsulating the hydrocarbon. When polymerizing at 62 °C, it was found that an initial AN/MAN feed ratio (fAN) between 0.15 and 0.9 results in core/shell particles with encapsulated hydrocarbon. fAN lower than 0.15 yielded solid particles with no hydrocarbon encapsulated while fAN higher than 0.9 yielded particles built up entirely from agglomerates of smaller primary particles. In contrast, when polymerizing at 80 °C, a much narrower span of fAN (0.5–0.85) yielded particles with hydrocarbon encapsulated. The influence on monomer conversion and the molecular weight of the polymer was also studied.
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| 7. |
- Liivat, Anti, et al.
(författare)
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A Molecular Dynamics Study of Short-Chain Ordering in Crystalline LiPF6PEO6
- 2007
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861 .- 1873-2291. ; 48:21, s. 6448-6456
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Tidskriftsartikel (refereegranskat)abstract
- Molecular dynamics (MD) simulations have been made of the crystalline short-chain LiPF6·PEO6 system to probe structural ordering for different chain-end arrangements for a methyl-terminated monodisperse poly(ethylene oxide) (EO23 Mw = 1059) host polymer. Five different start structures have been studied, two "smectic" and three "nematic", to represent different types of relative alignment of the end-groups between adjacent PEO chains, and different chain-end coordination situations to the Li-ions. One particular situation is found to result effectively in Li-ion bridging between PEO chains along the chain axes, thereby creating continuous ion transport pathways across the chain breaks. This situation is also found to give rise to Li+-PF6- ion-pairing and Li-O coordination instabilities in the end-group regions, where coordination to Li-ions would appear to have a more radical influence on local structure than the issue of smectic vs. nematic end-group alignment. It could be that such structural situations involving bridging Li-ions (in both smectic and nematic arrangements) are a necessary condition for the promotion of Li-ion transport in the chain direction. Comparison of simulated and experimental XRD profiles is concluded to be an inappropriately crude and uncertain technique for distinguishing between possible short-chain ordering models.
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| 8. |
- Mattozzi, Alessandro, et al.
(författare)
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Computer-built polyethylene spherulites for mesoscopic Monte Carlo simulation of penetrant diffusion : influence of crystal widening and thickening
- 2007
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861 .- 1873-2291. ; 48:8, s. 2453-2459
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Tidskriftsartikel (refereegranskat)abstract
- An algorithm able to mimic crystal lengthening, branching, widening and thickening was developed in order to build spherulites similar to those observed in polyethylene. The ranges of volume crystallinity and crystal width-to-thickness ratio attainable were <= 40% and 8-35, respectively. An on-lattice Monte Carlo-based algorithm was used to generate penetrant trajectories in the built spherulites. Diffusivity was assessed from the mean-square displacement of the penetrant molecules, normalized with respect to the mean-square displacement of the penetrant molecules in a crystal-free system, and compared with the geometrical impedance factor calculated from the Fricke theory using morphological data samples in the simulated spherulites. The crystal blocking effect was greater in the tangential plane than along the spherulite radius. All data, except that for the highest crystallinity system (40%), conformed to a linear relationship between the geometrical impedance factor obtained from the diffusivity data and the geometrical impedance factor calculated from morphological data; the latter being calculated according to the Fricke model using averages based on the squares of the crystal width-to-thickness ratio data. This finding suggests that wide crystals had a more pronounced effect on the geometrical impedance factor than was indicated by their number fraction weight. The system with the highest volume crystallinity (40%) showed a markedly higher geometrical impedance factor than predicted by the Fricke theory using the two aforementioned modifications.
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| 9. |
- Mattozzi, Alessandro, et al.
(författare)
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Morphological interpretation of n-hexane diffusion in polyethylene
- 2005
-
Ingår i: Polymer. - : Elsevier BV. - 0032-3861 .- 1873-2291. ; 46, s. 929-938
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Tidskriftsartikel (refereegranskat)abstract
- The diffusion of small-molecule penetrants in polyethylene is retarded by the detour caused by the crystals and by the segmental constraints imposed by the crystals on the penetrable phase. The earlier reported n-hexane diffusivity data for a series of homogeneous poly(ethylene-co-octene)s showed unexpectedly that the detour was greatest in the low crystallinity polymers. The crystal width-to-thickness ratio and the crystallinity were assessed by electron microscopy and differential scanning calorimetry and used in the Fricke model. The calculations showed that the geometrical impedance factor followed the same trend with increasing crystallinity as the data obtained from n-hexane desorption. The high geometrical impedance factor shown by the low crystallinity samples was due to the presence of crystals with an unusually high crystal width-to-thickness ratio. A unified relationship, including data for both linear and branched polyethylene was found between the fractional free volume and the phase composition of the penetrable phase including the liquid-like, interfacial liquid and the interfacial crystal core.
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| 10. |
- Núñez, Eugenia, et al.
(författare)
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Single crystal morphology of star polyesters with crystallisable poly(ε–caprolactone) arms
- 2005
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861 .- 1873-2291. ; 46:16, s. 5992-6000
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Tidskriftsartikel (refereegranskat)abstract
- Star-branched polymers consisting of poly(epsilon-caprolactone) (PCL) attached to third generation dendrimer, hyperbranched and dendron cores have been studied together with linear PCL analogues. The degree of polymerisation of the PCL arms of the star-branched polymers ranged from 14 to 81. Single crystals were grown from dilute solution and studied by transmission electron microscopy. Single crystals of linear PCL were multilayer hexagons with flat or slightly curved {110} and {100} faces. These single crystals were larger along [010] than along [100]. Single crystals of star-branched PCL showed the same basic shape, but with many crystallographic and irregular steps on the lateral crystal faces. The width of the micro-faces was typically 100-300 nm. These single crystals were more extended along [100] than along [010]. It is proposed that the high fold surface free energy and the constrained character of the star-branched polymers favour the formation of steps on the growth faces. Globular polycrystalline aggregates were also observed. They originated from a more concentrated polymer phase following phase separation of the solution. In the case of the star-branched polymers, lamellar branching was observed with a 30 angle between the crystals arms.
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| 11. |
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| 12. |
- Schut, J, et al.
(författare)
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Glass transition temperature prediction of polymers through the mass-per-flexible-bond principle
- 2007
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861 .- 1873-2291. ; 48:20, s. 6115-6124
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Tidskriftsartikel (refereegranskat)abstract
- A semi-empirical method based on the mass-per-flexible-bond (M/f) principle was used to quantitatively explain the large range of glass transition temperatures (T-g) observed in a library of 132 L-tyrosine derived homo, co- and terpolymers containing different functional groups. Polymer class specific behavior was observed in T-g vs. M/f plots, and explained in terms of different densities, steric hindrances and intermolecular interactions of chemically distinct polymers. The method was found to be useful in the prediction of polymer T-g. The predictive accuracy was found to range from 6.4 to 3.7 K, depending on polymer class. This level of accuracy compares favorably with (more complicated) methods used in the literature. The proposed method can also be used for structure prediction of polymers to match a target T-g value, by keeping the thermal behavior of a terpolymer constant while independently choosing its chemistry. Both applications of the method are likely to have broad applications in polymer and (bio)material science.
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| 13. |
- Wirsen, A., et al.
(författare)
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Solvent free vapour phase photografting of acrylamide onto poly(methyl methacrylate)
- 2005
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861 .- 1873-2291. ; 46:13, s. 4554-4561
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Tidskriftsartikel (refereegranskat)abstract
- Poly(methyl methacrylate) (PMMA) sheets were surface grafted with acrylamide under reduced pressure in a solvent free vapour of acrylamide and benzophenone. The grafting was initiated with UV irradiation and no pre-treatment of PMMA by impregnation or sorption of reactants was required. Characterization of grafted samples by ESCA and contact angles showed that the nitrogen content increased with grafting time and temperature. The surface bound amide groups obtained were converted into amine groups by the Hofmann reaction and used in coupling reactions with a p-nitrophenyl carbonate terminated PEG and 4,4,4-trifluoro butyraldehyde.
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| 14. |
- Andronova, Natalia, et al.
(författare)
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Potential tissue implants from the networks based on 1,5-dioxepan-2-one and epsilon-caprolactone
- 2005
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Ingår i: Polymer journal. - : Elsevier BV. - 0032-3896 .- 1349-0540. ; 46:18, s. 6746-6755
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Tidskriftsartikel (refereegranskat)abstract
- The synthesis and characterization of degradable polymeric networks for biomedical applications was performed. Cross-linked films of poly(epsilon-caprolactone) (PCL) and poly(1,5-dioxepan-2-one) (PDXO) having various mole fractions of monomers and different cross-link densities were successfully prepared using 2,2'-bis-(epsilon-caprolactone-4-yl) propane (BCP) as cross-linking agent. Reaction parameters were carefully examined to optimise, the film-formin.,, conditions. Networks obtained were elastomeric materials. easy to cast and remove from the mould. Effect of CL content and cross-link density on the final properties of the polymer network was evaluated. High CL content or degree of cross-linking led to increase in Young's modulus and decrease in elongation at break. An increase in crystalline domains in films having a higher CL content was observed by optical microscopy. A greater thermal stability was observed in films having a high CL content. The hydrophilicity of the materials could be tailored by changing the CL content. The surface of the films became rougher with higher CL content.
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| 15. |
- Andersson, L. H. U., et al.
(författare)
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The effect of different structure parameters on the crosslinking behaviour and network performance of LDPE
- 2006
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 47:1, s. 200-210
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Tidskriftsartikel (refereegranskat)abstract
- In the present study, we investigate the crosslinking behaviour of 6 ordinary low density polyethylenes, and the effect of relatively modest changes in the polyethylene structure on the properties of the resulting network. The observed variations in gel formation are mainly explained by differences in molecular weight, where both M̄n and M̄w affect the results. The presence of long chain branches (LCB) present on the polymer main chain is shown to have a significant effect on the network quality. The occurrence of LCB affects the ability in making effective entanglements, a behaviour which is largely dependent on the length of the branches. At high LCB frequencies, the long chain branches are relatively short and therefore more prone to disentangle. The frequency and the amount of LCB, together with the molecular weight, have a large impact on the coil size. The coil size is believed to be an important parameter for the crosslinking behaviour, as a large coil size facilitates interconnections between adjacent polymer coils. In addition, LCB increases the probability of creating intramolecular crosslinks. However, this study shows that a very high amount of LCB is needed in order to obtain any significant effect on the network quality originating from intramolecular crosslinks. © 2005 Elsevier Ltd. All rights reserved.
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| 16. |
- Colombini, Didier, et al.
(författare)
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The effect of the polymerization route on the amount of interphase in structured latex particles and their corresponding films
- 2005
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 46:4, s. 1295-1308
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Tidskriftsartikel (refereegranskat)abstract
- Three series of hard/soft styrene-acrylic latex based systems with equivalent compositions were prepared either by blending of homopolymer latexes or by preparing structured latex particles having core shell (CS) or inverted core shell (ICS) morphologies. Transmission electron microscopy (TEM) was used to investigate the particle morphologies, which were correlated to the calculated fractional radical penetration for the propagating species during the reactions. The thermo-mechanical properties as well as the morphology of the resulting latex films were analyzed by differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and TEM. The viscoelastic properties of the interphase between the first and second-stage polymers formed in the structured hard/soft latex films, as well as its qualitative amount and also the film morphologies were found to depend on the interplay between thermodynamic and kinetic parameters during the synthesis of the samples. (C) 2004 Elsevier Ltd. All rights reserved.
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| 17. |
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| 18. |
- Edgecombe, Samuel, et al.
(författare)
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Monte Carlo simulation of two interpenetrating polymer networks: Structure, swelling, and mechanical properties
- 2008
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 49:7, s. 1981-1992
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Tidskriftsartikel (refereegranskat)abstract
- The swelling and mechanical properties of various interpenetrating polymer networks (IPNs) were studied. Six networks made from permutations of a moderately crosslinked polyelectrolyte network (ref), a moderately crosslinked neutral polymer network (net1), and a highly crosslinked polyelectrolyte network (net2) were first swollen in water and structural properties such as end-to-end chain lengths and radial distribution functions were compared with the component networks' equilibrium properties. The swelling of composite IPNs was discussed in terms of a balance between the osmotic pressure due to mobile counterions and the restoring force of the network chains, which act in parallel to counteract the osmotic swelling. For the ref-net2 system, the strong stretching of net2 chains increases the network restoring force and the further swelling due to the counterions is suppressed. The swollen networks were then uniaxially stretched, and equilibrium stress-strain plots were obtained up to high extension ratios. The equilibrium volume decreased upon uniaxial extension, and the elastic moduli of IPNs of the A-A type were slightly greater than that of their respective single networks.
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| 19. |
- Kirsebom, Harald, et al.
(författare)
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In situ H-1 NMR studies of free radical cryopolymerization
- 2008
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 49:18, s. 3855-3858
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Tidskriftsartikel (refereegranskat)abstract
- Free radical polymerization of DMAAm (dimethylacrylamide)-co-PEG diacrylate in a semi-frozen aqueous solution was studied using H-1 NMR, which enables to monitor the non-frozen water as well as the reaction of monomers over time. It was possible to confirm the presence of a heterogeneous system with a liquid phase where the monomers were concentrated and the reaction proceeded. The resulting macroporous polymeric structure with dense pore walls was confirmed using scanning electron microscopy (SEM). (C) 2008 Elsevier Ltd. All rights reserved.
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| 20. |
- Knaapila, Matti, et al.
(författare)
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An effect of side chain length on the solution structure of poly(9,9-dialkylfluorene)s in toluene
- 2008
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 49:8, s. 2033-2038
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Tidskriftsartikel (refereegranskat)abstract
- The effect of side chain length of pi-conjugated poly(9,9-dialkylfluorene)s has been studied in semi-dilute (10 mg/mL) toluene solutions using small-angle neutron scattering (SANS) and H-1 and H-2 NMR spectroscopies. Under these conditions, SANS data indicate that poly(9,9-dinonylfluorene) and poly(9,9-dioctylfluorene) are dissolved down to the molecule level and appear as elongated one-dimensional chains (length >20-30 nm). In contrast, the shorter side chain polymers exhibit a self-association so that poly(9,9-diheptylfluorene) forms thin sheet-like (similar to 1 nm) and poly(9,9-dihexylfluorene) thin (similar to 1 nm) and thick sheet-like (>6 nm) aggregates. H-1 NMR data, together with the density functional theory (DFT) calculations, however, show that this occurs without changes in the conformation of the polymer backbone.
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| 21. |
- Kuzimenkova, Marina, et al.
(författare)
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Optical responses, permeability and diol-specific reactivity of thin polyacrylamide gels containing immobilized phenylboronic acid
- 2008
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 49:6, s. 1444-1454
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Tidskriftsartikel (refereegranskat)abstract
- Thin semitransparent gels were prepared by radical copolymerization of N-acryloyl-m-aminophenylboronic acid (NAAPBA) and acrylamide (AAm) taken in molar ratios from 8:92 to 16:84, respectively, in water. The gels were characterized by the content of immobilized NAAPBA and monomer conversion. Scanning electron microscopy revealed the micrometer size pores in the dried gels. The wet gels displayed a linear optical response to sugars with sensitivity decreasing in the series: D-fructose, D-galactose, D-glucose, D-mannose, N-acetyl-D-glucosamine in the sugar concentration range from 1 to 40-60 mM at pH 7.3. Cross-linking of the gels with N,N-methylene-bis-acrylamide decreased the strength of optical response. Specific binding capacity of a diol-containing dye Alizarin Red S in the gels at pH 7.0 coincided with the content of immobilized NAAPBA indicating the 1: 1 stoichiometry of the reaction and, therefore, good accessibility of the boronic acid ligands for water-soluble diols. Permeability of the gels was studied with a non-interacting dye Ethyl Orange exhibiting the pore diffusion coefficient of 1.4 x 10(-7) cm(2)/s. The rate of optical response of the gels to glucose was found to be determined by diffusion of sugar into the relatively thick gels (1 = 0.35-1 mm) with effective diffusion coefficients of 2 x 10(-7) cm(2)/S. In the thinner gels (l = 0.1 mm) the input of other kinetic processes, such as affinity binding or structural rearrangements of the gel, was noticeable. (c) 2008 Elsevier Ltd. All rights reserved.
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| 22. |
- Loyens, Wendy, et al.
(författare)
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Effect of clay modifier and matrix molar mass on the structure and properties of poly(ethylene oxide)/Cloisite nanocomposites via melt-compounding
- 2005
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 46:3, s. 903-914
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Tidskriftsartikel (refereegranskat)abstract
- The present study is concerned with the preparation and characterisation of PEO/clay nanocomposites via melt-extrusion. Two different matrix molar masses of PEO were investigated as well as various types of the Cloisite clay range. PEO/Cloisite Na+ nanocomposites give rise to intercalated structures displaying only a moderate improvement of the mechanical properties at higher clay concentrations, regardless of the matrix molar mass. The chemical nature of the organic modifier was proven to be detrimental for the final nanocomposite structure and resulting mechanical properties. PEO nanocomposites based on the Cloisite 30B clay, incorporating a polar modifier, give rise to exfoliated structures. They display a strongly increased storage modulus, regardless of the matrix molar mass. The structural organisation of the nanocomposites based on Cloisite 20A, containing an apolar modifier, is very dependent on the matrix molar mass. An exfoliated structure can only be achieved upon melt mixing with a high molar mass PEO. In general, the mechanical properties of the nanocomposites based on the high molar mass PEO matrix are slightly superior. The thermal properties are also distinctly influenced by the addition of clay, although the actual structural organisation of the nanocomposite is proven to be less important. The melt temperature, as well as the crystallinity, decreases upon the addition of clay, especially for the low molar mass PEO matrix. The decomposition temperature shows a slight increase upon the addition of clay, especially for the Cloisite 30B nanocomposites.
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| 23. |
- Loyens, Wendy, et al.
(författare)
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Melt-compounded salt-containing poly(ethylene oxide)/clay nanocomposites for polymer electrolyte membranes
- 2005
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 46:18, s. 7334-7345
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Tidskriftsartikel (refereegranskat)abstract
- The present study demonstrates the use of a simple and versatile melt-compounding route to prepare NaClO4-containing poly(ethylene oxide) PEO/clay nanocomposites combining excellent mechanical properties with a competitive level of the ionic conductivity. The nanostructure and the resulting thermal, mechanical and conductive properties of the salt-containing PEO/clay nanocomposites were found to be highly sensitive to the clay type, i.e. aspect ratio of the clay, to the presence of an organic modifier in the intergallery spacing, and to the salt concentration. The highest increase of the shear storage modulus is obtained in the presence of single silicate layers, thus an exfoliated nanostructure, having a high aspect ratio. These structures are only obtained with an (polar) organically modified clay (Cloisite 30B), regardless of the presence of salt. The use of non-organically modified clays (Cloisite Na+ and Laponite) resulted in intercalated nanocomposites, with only a minor improvement in stiffness. A strong interaction between the Na+ from NaClO4 and the Cloisite 30B silicate layers might be responsible for an increased PEO crystallinity and resultant additional increase in stiffness. A mechanism is proposed whereby the Na+ ions are drawn away from the PEO phase, to be complexed by the silicate layers, or even ion-exchanged with modifier cations. The addition of clay did not greatly affect the ion conductivity below the melt temperature of PEO. At higher temperatures, the nanocomposites displayed only slightly lower conductivities compared to the PEO/NaClO4 complex, due to the presence of the clay platelets.
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| 24. |
- Loyens, Wendy, et al.
(författare)
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Poly(ethylene oxide)/Laponite nanocomposites via melt-compounding: effect of clay modification and matrix molar mass
- 2005
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 46:3, s. 915-928
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Tidskriftsartikel (refereegranskat)abstract
- The present study focuses on the preparation of poly(ethylene oxide) (PEO) nanocomposites based on the synthetic Laponite clay. The clay was added both in its pure form as well as organically modified with low molar mass poly(ethylene glycol) (PEG) components in order to enhance the compatibility between Laponite and PEO. Several PEG's with different end groups were used. Almost all of them were found to intercalate in the clay intergallery spacing. An order of intercalation efficiency could be established. The modified clays displayed a good thermal stability at the nanocomposite processing temperature. The nanocomposites based on the pure Laponite clay as well as the modified clays display an intercalated structure with a modest intergallery spacing. The ion-dipole modification with the PEG's was ineffective in improving the compatibility between PEO and the Laponite silicate layers. Their respective mechanical properties were found to be increased a little, which can be attributed to the low effective aspect ratio of the silicate platelets present in the nanocomposites. This is caused by the low initial aspect ratio of Laponite (w/t= 25) and the limited basal spacing increase. The addition of clay does not result in nucleation of the PEO crystallisation. In contrast, the crystallisation was inhibited, resulting in decreased heat of fusions, especially for the pure Laponite nanocomposites. The nanocomposites based on the modified Laponites display a good thermal stability.
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| 25. |
- Mahlin, D., et al.
(författare)
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Influence of polymer molecular weight on the solid-state structure of PEG/monoolein mixtures.
- 2005
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 46:26, s. 12210-12217
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Tidskriftsartikel (refereegranskat)abstract
- The polar lipid monoolein (MO) and poly(ethylene glycol), PEG, of different molar mass (1500, 4000 and 8000) were melted, mixed and left to solidify at room temperature. Analysis of the solid mixtures by differential scanning calorimetry (DSC) and small angle X-ray scattering (SAXS) revealed that a phase separation occurs when MO is present in sufficient amounts. The molecular weight of the polymer determines the amount of MO that has to be added before a separate MO phase can be detected. To further understand this behaviour, the folding of the polymers and the thickness of the amorphous domains within the lamellar structure of PEG were determined by calculation of the one-dimensional correlation function from the experimental SAXS data. It revealed that the presence of MO makes the crystalline domains of PEG 1500, which crystallizes unfolded, increase at the expense of the amorphous domains. PEG 4000 and PEG 8000 obtain a higher degree of folding when the MO content in the mixtures increases. Furthermore, a second form of MO was detected when it phase separated from PEG 1500 and 4000. This behaviour was argued to be due to the secondary crystallization of the PEGs.
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| 26. |
- Mattozzi, Alessandro, et al.
(författare)
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Diffusivity of n-hexane in poly(ethylene-co-octene)s assessed by molecular dynamics simulations
- 2007
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 48:17, s. 5174-5180
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Tidskriftsartikel (refereegranskat)abstract
- Molecular dynamics simulations have been used to study diffusion of n-hexane in wholly amorphous poly(ethylene-stat-octene)s with comonomer contents ranging from 0 to 11.5 mol%. The branches in the polymer increased the specific volume by affecting the packing of the chains in the rubbery state in accordance with experimental data. The diffusion of n-hexane at penetrant concentrations between 0.5 and 9.1 wt% was simulated within time-scales between 0.1 and 0.2 μs. The penetrant diffusivity unexpectedly decreased with increasing comonomer content. The penetrant molecule motion statistics showed that systems with high comonomer content showed a greater tendency for short distance motion (over a sampling period of 3 ps) whereas the systems with lower comonomer content showed penetrant motion over longer distances. It seems that the branches retarded local chain mobility of the polymer thereby trapping the penetrant molecules. All systems studied showed a minimum in penetrant diffusivity at ca. 1 wt% n-hexane and a marked increase in diffusivity at higher penetrant concentrations. The volumetric data for the different polymer–penetrant systems were consonant with additional volumes of the different components. Comparison between simulated diffusivities (for a wholly amorphous polymer) and experimentally obtained diffusivity data for semicrystalline polymers showed that constraining effect of the crystals were substantial for the highly crystalline systems and that it gradually decreased with decreasing crystallinity.
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| 27. |
- Mattozzi, Alessandro, et al.
(författare)
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Mesoscale modelling of penetrant diffusion in computer-generated polyethylene-spherulite-like structures
- 2006
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 47, s. 5588-5595
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Tidskriftsartikel (refereegranskat)abstract
- Molecular dynamics simulations have been used to study diffusion of n-hexane in wholly amorphous poly(ethylene-stat-octene)s with comonomer contents ranging from 0 to 11.5 mol%. The branches in the polymer increased the specific volume by affecting the packing of the chains in the rubbery state in accordance with experimental data. The diffusion of n-hexane at penetrant concentrations between 0.5 and 9.1 wt% was simulated within time-scales between 0.1 and 0.2 μs. The penetrant diffusivity unexpectedly decreased with increasing comonomer content. The penetrant molecule motion statistics showed that systems with high comonomer content showed a greater tendency for short distance motion (over a sampling period of 3 ps) whereas the systems with lower comonomer content showed penetrant motion over longer distances. It seems that the branches retarded local chain mobility of the polymer thereby trapping the penetrant molecules. All systems studied showed a minimum in penetrant diffusivity at ca. 1 wt% n-hexane and a marked increase in diffusivity at higher penetrant concentrations. The volumetric data for the different polymer–penetrant systems were consonant with additional volumes of the different components. Comparison between simulated diffusivities (for a wholly amorphous polymer) and experimentally obtained diffusivity data for semicrystalline polymers showed that constraining effect of the crystals were substantial for the highly crystalline systems and that it gradually decreased with decreasing crystallinity.
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| 28. |
- Munch Elmér, Anette, et al.
(författare)
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Gel electrolyte membranes derived from co-continuous polymer blends
- 2005
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 46:19, s. 7896-7908
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Tidskriftsartikel (refereegranskat)abstract
- Polymer gel electrolyte membranes were prepared by first casting films of poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) salt, and poly(ethylene glycol) (PEG) monomethacrylate and dimethacrylate macromonomers. Polymerization of the macromonomers initiated by UV-irradiation then generated solid films having phase-separated morphologies with a microporous PVDF-HFP phase embedded in PEG-grafted polymethacrylates. Gel electrolyte membranes were finally prepared by allowing the films to take up solutions of LiTFSI in gamma-butyrolactone (gamma-BL). The PEG-grafted polymethacrylate in the membranes was found to host the largest part of the liquid electrolyte, giving rise to a highly swollen ionic conductive phase. Results by FTIR spectroscopy showed that the Li+ ions preferentially interacted with the ether oxygens of the PEG chains. The properties of the membranes were studied as a function of the ratio of PVDF-HFP to PEG-grafted polymethacrylate, as well as the degree of crosslinking, LiTFSI concentration, and liquid electrolyte content. The self-supporting and elastic gel membranes had ionic conductivities of 10(-3) S cm(-1) and a mechanical storage modulus in the range of 2.5 MPa in the tension mode at room temperature. Variation of the salt concentration showed the greatest effect on the membrane properties.
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| 29. |
- Persson, Christian, et al.
(författare)
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Polysulfones tethered with benzimidazole
- 2006
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 47:4, s. 991-998
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Tidskriftsartikel (refereegranskat)abstract
- Benzimidazole units have been grafted onto a polysulfone (PSU) backbone via long alkyl thio–ether chains using a two-step procedure. In the first step, lithiated PSU was reacted with 10-undecenoyl chloride to graft PSU with undecenoyl side chains. The second step involved a free-radical thiol–ene coupling reaction between the C=C bonds of the pendant undecenoyl chains and 2-(2-benzimidazolyl)ethanethiol. In this reaction, all the C=C bonds were converted into thio–ether linkages without any detectable structural degradation, as confirmed by 1H NMR spectroscopy and size-exclusion chromatography. The procedure constitutes a convenient and general pathway to attach functional or mesogenic groups to PSU via long flexible spacers. Thermogravimetry showed that the benzimidazole-functionalized polymers were stable up to 250 °C under nitrogen atmosphere, and that the first degradation step was attributed to the cleavage of the thio–ether bond. While the grafting of the undecenoyl side chains was found to significantly decrease the glass transition temperature (Tg), the subsequent tethering of the benzimidazole only slightly increased the Tg of the grafted PSU backbone. The concentration of benzimidazole was probably too low for the formation of a percolating benzimidazole domain. This explains the quite modest proton conductivity measured under completely dry conditions, e.g. 34 nS/cm at 180 °C for a polymer functionalized with 1.7 benzimidazole units per repeating unit of PSU.
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| 30. |
- Savina, Irina, et al.
(författare)
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Graft polymerization of acrylic acid onto macroporous polyacrylamide gel (cryogel) initiated by potassium diperiodatocuprate
- 2005
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 46:23, s. 9596-9603
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Tidskriftsartikel (refereegranskat)abstract
- Potassium diperiodatocuprate-initiated graft polymerization was found to be an efficient and convenient method for grafting of acrylic acid (AAc) onto superporous polyacrylamide gels, so called cryogels (pAAm cryogels). It was possible to achieve grafting degrees as high as 70% with about 25% yield of grafted polymer with respect to the initial amount of monomer. The superporous structure of the cryogels promoted grafting by providing an ample surface of the gel for grafting, ensuring good mass transfer inside the gel sample and allowing to wash easily both homopolymer of AAc and insoluble by-products formed during the polymerization reaction. The grafted cryogels could be dried at 60 degrees C and re-swollen with retaining their properties. The adsorption of water vapours by dried pAAm cryogels was marginally dependent on the degree of grafting. The swelling of AAc-grafted pAAm cryogel increased pronouncedly with increasing pH. The adsorption of low-molecular weight ligand, Cu(II), by AAc-grafted pAAm cryogels increased linearly with the degree of grafting, while binding of high-molecular weight ligand, lysozyme, increased linearly till the degree of grafting of about 40% followed by a sharp, nearly three-fold increase in lysozyme binding when the degree of grafting increased from 60 to 70%. The results indicate that a 'tentacle'-type binding of lysozyme to grafted polyAAc takes place after a certain degree of grafting has been reached. (c) 2005 Elsevier Ltd. All rights reserved.
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| 31. |
- Trotzig, Charlotte, et al.
(författare)
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Structure and mobility in water plasticized poly(ethylene oxide)
- 2007
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 48:11, s. 3294-3305
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Tidskriftsartikel (refereegranskat)abstract
- The change in structure and mobility of poly(ethylene oxide) (PEO) containing 2 wt% of fumed silica and the water self-diffusion coefficient in concentrated PEO-water systems have been investigated at room temperature in the water weight fraction, w(w) range 0-0.50 w/w. Pulsed field gradient nuclear magnetic resonance was used to measure the self-diffusion coefficients. Structure and mobility properties of PEO were measured with differential scanning calorimetry as well as with positron annihilation lifetime spectroscopy. The largest reduction of the degree of crystallinity of PEO was observed when ww was increased from 0.13 w/w to 0.50 w/w. Moreover, water induced relaxation of the PEO segments in the amorphous phase, which seemed to have been strained by the crystals during compression molding. The water self-diffusion coefficient increased logarithmically with increased water content below water weight fractions in the amorphous phase of 0.30 w/w and the water molecules were obstructed by the crystalline phase.
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| 32. |
- Winberg, Petra, et al.
(författare)
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Free volume sizes in intercalated polyamide 6/clay nanocomposites
- 2005
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861. ; 46:19, s. 8239-8249
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Tidskriftsartikel (refereegranskat)abstract
- The effect of incorporating modified clay into a polyamide 6 (PA6) matrix, on the free volume cavity sizes and the thermal and viscoelastic properties of the resulting nanocomposite, was studied with positron annihilation lifetime spectroscopy, differential scanning calorimetry and dynamic mechanical analysis. At low concentrations of clay the fraction of PA6 crystals melting close to 212 degrees C was increased, while the fraction of the a-form PA6 crystals, melting close to 222 degrees C, was reduced. At higher concentrations of clay, a crystal phase with increased thermal stability emerged. Addition of more than 19 wt% clay caused a reduction of the heat of fusion of PA6. An unexpected reduction of the Delta C-p at the glass transition, contradicting the measured reduction of the heat of fusion, was detected, indicating an altered mobility in the non-crystalline regions. The viscoelastic response of PA6/clay nanocomposites, as compared to unfilled PA6, pointed towards a changed mobility in the non-crystalline regions. At high concentrations of clay (> 19 wt%) an increase of the free volume cavity diameter was observed, indicating a lower chain packing efficiency in the PA6/clay nanocomposites. The increased free volume sizes were present both above and below the glass transition temperature of PA6. (c) 2005 Elsevier Ltd. All rights reserved.
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