| 1. |
- BAKKER, ALBERT, et al.
(författare)
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CONTACT ION-PAIR FORMATION AND ETHER OXYGEN COORDINATION IN THE POLYMER ELECTROLYTES M[N(CF3SO2)(2)](2)PEO(N) FOR M=MG, CA, SR AND BA
- 1995
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Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 36:23, s. 4371-4378
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Tidskriftsartikel (refereegranskat)abstract
- The polymer electrolytes M[N(CF3SO2)(2)](2)PEO(n) for M = Mg, Ca, Sr and Ba have been investigated using infra-red spectroscopy, differential scanning calorimetry and impedance spectroscopy. The effects of varying concentration (n = 6-40) and temperature (25-95 degrees C) on the contact ion pair formation and cation coordination have been studied. Contact ion pairs are only found for the most concentrated samples (n < 9). Ion pairs occur with two types of structures: one type is found far samples containing Mg2+ and the other for samples with Ca2+, Sr2+ and Ba2+. The conductivities of the samples are discussed in terms of radii and coordination numbers of the cations.
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| 2. |
- Bakker, Albert, et al.
(författare)
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Polymer electrolytes based on triblock-copoly(oxyethylene/oxypropylene/oxyethylene) systems
- 1996
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861 .- 1873-2291. ; 37:10, s. 1871-1878
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Tidskriftsartikel (refereegranskat)abstract
- Polymer electrolytes based on triblock copolymers of ethylene oxide (EO)/propylene oxide (PO)/ethylene oxide of moderate molecular weight and narrow block-length distributions, doped with M(CF3SO3)(2) and M[N(CF3SO2)(2)](2) (M = Mg, Ca, Sr and Ba), LiCF3SO3 and LiN(CF3SO2)(2) have been investigated using infrared spectroscopy, differential scanning calorimetry and conductivity measurements. The effects of varying the EO/PO block length, composition and temperature on the phase behaviour, ion-pair formation and conductivity of the polymer electrolytes have been studied. A two-phase microstructure has been observed. Ion pairing occurs for the triflate salts and the amount was found to be sensitive to the relative block sizes rather than the molecular weight of the copolymer. Copyright (C) 1996 Elsevier Science Ltd.
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| 3. |
- Cacialli, F., et al.
(författare)
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Synthesis and characterisation of poly(distyrylbenzene-block-hexa(ethylene oxide)) and its fluorinated analogue - Two new block copolymers and their application in electroluminescent devices
- 2002
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Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 43:12, s. 3555-3561
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Tidskriftsartikel (refereegranskat)abstract
- Two new soluble block copolymers are reported in which chromophores and hexa(ethylene oxide) units alternate along the polymer backbone. In polymer 1 the chromophore was the distyrylbenzene unit. The polymer was synthesised via the Wittig reaction and the ionization potential of 5.4 ± 0.2 eV was measured by cyclic voltammetry and photoelectron spectroscopy. Polymer 1 showed a high solid-state photoluminescence efficiency (34%) and was used to make efficient (0.5 cd/A) light emitting diodes (LEDs). Polymer 1 was also used in light emitting cells, these showed luminescence in reverse bias and a reduced turn-on voltage compared to the LEDs. Polymer 2, in which the chromophore was dodecafluoro-distryrylbenzene, was prepared via the Horner-Wittig reaction and showed an ionization potential of 6.25 ± 0.15 eV and a solid-state photoluminescence efficiency of 17%. It was used as electron-conducting layer in a LED but failed to give significant electroluminescence. The optical energy gap for both polymers was 3.0 eV. © 2002 Published by Elsevier Science Ltd.
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| 4. |
- Carlmark, Anna E, et al.
(författare)
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Atom transfer radical polymerization of methyl acrylate from a multifunctional initiator at ambient temperature
- 2002
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Ingår i: Polymer. - OXFORD, ENGLAND : ELSEVIER SCI LTD. - 0032-3861 .- 1873-2291. ; 43:15, s. 4237-4242
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Tidskriftsartikel (refereegranskat)abstract
- A multifunctional initiator for ATRP has been synthesized by reacting a hyperbranched polyether, based on 3-ethyl-3-(hydroxymethyl)oxetane, with 2-bromo-isobutyrylbromide. The macroinitiator contained approximately 25 initiating sites per molecule. It was used for the atom transfer radical polymerization of methyl acrylate mediated by Cu(I)Br and tris(2-(dimethylamino)ethyl)amine (Me-6-TREN) in ethyl acetate at room temperature. This yielded a co-polymer with a dendritic-linear architecture. The large number of growing chains from each macromolecule increases the probability of inter-and intramolecular reactions. In order to control these kinds of polymerizing systems and prevent them from forming a gel, the concentration of propagating radicals must be kept low. The polymerizations under these conditions were well controlled. When a ratio of initiating sites-to-catalyst of 1:0.05 was used, the polymers from all of the reactions had a low polydispersity, ranging from 1.1 to 1.4. None of the polymerizations under these conditions gave gelation. Monomer conversions as high as 65% were reached while maintaining control over the polymerization. (C) 2002 Elsevier Science Ltd. All rights reserved.
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| 5. |
- Claesson, Hans, et al.
(författare)
-
Synthesis and characterisation of star branched polyesters with dendritic cores and the effect of structural variations on zero shear rate viscosity
- 2002
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Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 43:12, s. 3511-3518
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Tidskriftsartikel (refereegranskat)abstract
- A series of branched polyesters consisting of poly(epsilon-caprolactone) (PCL) (degree of polymerisation: 5-200) initiated from hydroxy-functional cores and end-capped with methylmethacrylate have been prepared. The cores were third-generation hyperbranched polyester, Boltorn, with approximately 32 hydroxyl groups, a third-generation dendrimer with 24 hydroxyl groups and a third-generation dendron with eight hydroxyl groups. Finally, a linear PCL was synthesised as a reference material. All initiators were based on 2,2-bis(methylol) propionic acid (bis-MPA). C-13 NMR spectra of the polymers showed that those with shorter arms contained unreacted hydroxyl groups on the core. Rheological measurements of zero shear rate viscosity, eta(0), showed that the branched polyesters had a considerably lower eta(0) than linear polyester with similar molecular weight. The low melt viscosity and the crystallity produced a theological behaviour suitable for the film formation process for powder coatings. Measurements of mechanical properties of cured films showed that those with low arm molecular weight, M-a, were amorphous while those of high M-a were crystalline.
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| 6. |
- Cordova, A, et al.
(författare)
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Lipase-catalysed formation of macrocycles by ring-opening polymerisation of epsilon-caprolactone
- 1998
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Ingår i: Polymer. - : Elsevier BV. - 0032-3861 .- 1873-2291. ; 39:25, s. 6519-6524
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Tidskriftsartikel (refereegranskat)abstract
- Studies were undertaken to gain mechanistic information on lactone ring-opening polymerisation reactions using Candida antarctica lipase B (Novozym 435) as the catalyst and epsilon-caprolactone as the monomer. Polymerisations were performed in organic solvents as well as without solvent at 60 degrees C. Candida antarctica lipase B catalysed concurrently with the intermolecular ring-opening polymerisation, and also the formation of macrocycles by an intramolecular condensation reaction. Candida antarctica lipase B had the highest initial rate of consumption of epsilon-caprolactone (1.2 mu mol mg(-1) min(-1)) in the bulk polymerisation, without solvent. Under these conditions, the highest average M-w, 4701 D, of poly(epsilon-caprolactone) was obtained. There were small amounts of cyclic oligomers present. When comparing the polymerisations performed in dioxane, acetonitrile and THF after 24 h reaction time with the bulk polymerisation, the average M-w of poly(epsilon-caprolactone) [2984, 1297, 1862 D, respectively] and the initial rates of monomer conversion of the enzyme (0.1, 0.05, 0.013 mu mol mg(-1) min(-1), respectively) were lower, however, the formation of cyclic oligomers was high. In dioxane, macrocycles of up to 2623 D corresponding to 23 monomer units were formed, and in acetonitrile there were mostly cyclic oligomers present. (C) 1998 Elsevier Science Ltd. All rights reserved.
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| 7. |
- Ericson, Mats L., et al.
(författare)
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Design and potential of instrumented ultramicrotomy
- 1997
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Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 38:17, s. 4485-4489
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Tidskriftsartikel (refereegranskat)abstract
- Ultramicrotomes are generally used for preparation of very thin sections for transmission electron microscopy. Recently it has been shown that when the sample holder of the ultramicrotome is instrumented with a force transducer, it is possible to measure the very small sectioning force during sectioning, and calculate the energy dissipated. In the present work, the instrumentation is further improved. The new sample holder, which uses two piezo-electric force transducers can measure two force components simultaneously. It is not only robust and stiff, but it also shows high sensitivity and reproducibility. It is possible to detect sectioning forces lower than 0.1 mN. The method is demonstrated on two amorphous polymers, poly(methyl methacrylate) and epoxy. Fracture energies in the same order of magnitude as theoretical predictions from chemical bond fracture only are recorded. It is therefore suggested that the method of instrumented ultramicrotomy is a useful tool when information on covalent bond density is needed. Potential future applications are identified including research on nano-scale fracture, characterization of molecular anisotropy and developments of the ultramicrotome
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| 8. |
- Ferry, Anders, et al.
(författare)
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Raman, infra-red and d.s.c. studies of lithium coordination in a thermoplastic polyurethane
- 1996
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Ingår i: Polymer. - : Elsevier. - 0032-3861 .- 1873-2291. ; 37:5, s. 737-744
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Tidskriftsartikel (refereegranskat)abstract
- Fourier transform (FT)-Raman and infra-red (i.r.) spectroscopy were utilized to monitor changes in the morphology of a commercial, phase-segregated thermoplastic polyurethane (TPU) as a function of LiClO4 concentration (0.1 to 2.0 mmol/g TPU). Significant changes in both the FT-Raman and the FTi.r. spectra were detected which suggest a competition between hydrogen bonding and lithium cation coordination, especially between the hard segments of the host polymer matrix. A loss in long-range ordering of the hard domain was observed by differential scanning calorimetry with an increase in salt concentration. The ionic conductivity (σ) was found to increase with increasing temperature and salt concentration. For the highest concentration used, σ ranged from a very low value of ∼ 1 x 10-9 S cm-1 at room temperature to ∼ 1 x 10-4 S cm-1 at 130 degrees C.
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| 9. |
- Gallet, G., et al.
(författare)
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Thermal degradation of poly(ethylene oxide-propylene oxide-ethylene oxide) triblock copolymer : comparative study by SEC/NMR, SEC/MALDI-TOF-MS and SPME/GC-MS
- 2002
-
Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 43:4, s. 1081-1094
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Tidskriftsartikel (refereegranskat)abstract
- By comparing size exclusion chromatography/matrix assisted laser desorption ionisation (SEC/MALDI) and SEC/NMR spectra from virgin poly(ethylene oxide-propylene oxide-ethylene oxide) triblock copolymer, we were able to understand the bimodal distribution observed in poloxamer 407. Propylene oxide, isomerised to allyl alcohol during polymerisation, eventually forms a Poly(ethylene oxide-propylene oxide) diblock copolymer when EO is added to the feed. The oxidative thermal degradation of poloxamer 407 at 80 degreesC in air was studied. We found by MALDI that degradation starts after 21 days in the PPO block of the copolymer. This result was confirmed by solid phase microextraction/gas chromatography-mass spectrometry (SPME/GC-MS): The first volatile degradation product to appear is 1,2-propanediol,1-acetate,2-formate. The structure of this molecule suggests that a six-ring intramolecular decomposition reaction of the PPO chain occurs at the very beginning of the polymer breakdown. Thus, the secondary hydroperoxide formed on the PPO chain plays a major role on the thermoxidation of poloxamer materials.
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| 10. |
- Glauser, T, et al.
(författare)
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Electron-beam curing of thick thermoset composite matrices
- 1999
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Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 40, s. 5297-5302
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Tidskriftsartikel (refereegranskat)abstract
- Electron-beam (EB) curing of two epoxy resins, one acrylated and one methacrylated, has been investigated. The change in thermomechanical properties, such as T-g, and the change of residual unsaturation have been studied as a function of dose. These results, in combination with in situ measurements of the temperature during cure, have shown the importance of sample geometry for the final properties of the thermoset. The thermal history of the sample during cure greatly affects the properties of the cured resin. (C) 1999 Elsevier Science Ltd. All rights reserved.
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| 11. |
- Hakkarainen, Minna, et al.
(författare)
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Rapid (bio)degradation of polylactide by mixed culture of compost microorganisms - low molecular weight products and matrix changes
- 2000
-
Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 41:7, s. 2331-2338
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Tidskriftsartikel (refereegranskat)abstract
- Poly(L-lactide) (PLLA) was rapidly (bio)degraded by a mixed culture of compost microorganisms. After 5 weeks in biotic environment, the films had fragmented to fine powder, while the films in corresponding abiotic medium still looked intact. Analysis of the low molecular weight products by GC-MS showed that microorganisms rapidly assimilated lactic acid and lactoyl lactic acid from the films. At the same time, a new degradation product, ethyl ester of lactoyl lactic acid was formed in the biotic environment. This product cannot be formed by abiotic hydrolysis and it was not detected in the abiotic medium. The degradation of the PLLA matrix was monitored by differential scanning calorimetry (DSC), size exclusion chromatography (SEC) and scanning electron microscopy (SEM). A rapid molecular weight decrease and increasing polydispersity was observed in the biotic environment. In the abiotic environment only a slight molecular weight decrease was seen and the polydispersity started decreasing towards 2.0. This indicates different degradation mechanisms, i.e. preferred degradation near the chain ends in the biotic environment and a random hydrolysis of the ester bonds in the abiotic environment. SEM micrographs showed the formation of patterns and cracks on the surface of the films aged in biotic medium, while the surface of the sterile films remained smooth. The SEM micrographs showed a large number of bacteria and mycelium of fungi growing on the surface of the biotically aged films.
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| 12. |
- Hedenqvist, Mikael S., et al.
(författare)
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The significance of the zero-concentration diffusivity value obtained from integral desorption data
- 2002
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Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 43:1, s. 223-226
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Tidskriftsartikel (refereegranskat)abstract
- n-Hexane zero-concentration diffusivity in high density polyethylene obtained 'indirectly' from integral desorption measurements using the free volume concept was compared with the zero-concentration diffusivity obtained directly at low-n-hexane activities using a quartz-ring system. The difference between the results obtained by the indirect and direct methods was within the experimental error. The concentration dependence of the diffusivity predicted by the Cohen-Turnll-Fujita free volume theory was in accordance with experimental data.
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| 13. |
- Hedenqvist, Mikael S., et al.
(författare)
-
Transport properties of hyperbranched and dendrimer-like star polymers
- 2000
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Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 41:5, s. 1827-1840
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Tidskriftsartikel (refereegranskat)abstract
- Moisture transport properties were assessed by sorption and desorption measurements on hydroxyl-functional hyperbranched polyesters based on 2,2-bis(methylol) propionic acid (bis-MPA) as AB(2)-monomer with ethoxylated pentaerythritol. A series of these polymers with different molar masses were studied. For the first time, it is reported that sigmoidal sorption curves were successfully modelled using a time-dependent surface boundary concentration, where the relaxation time was obtained from the mechanical stress relaxation data. The zero concentration diffusivities were very small and comparable with the values of fully amorphous poly(vinyl alcohol). Both the diffusivity data and the stress relaxation data indicated that these materials were plasticized by moisture. Ethylene glycol transport properties were measured on a hexadecanoate(C16)-terminated bis-MPA hyperbranched polymer. The replacement of the hydroxyl groups with C16 paraffin tails resulted in an increase in solute diffusivity despite the fact that these polymers became semicrystalline. The shape of the desorption curves indicated that continuous micropores were present and facilitated mass transport. The moisture transport properties were also measured on a series of semicrystalline dendrimer-like star poly(epsilon-caprolactone(s)). The low measured densities of these highly crystalline dendrimers confirmed that the porosity, as indicated by the shape of the desorption curves, had to be discontinuous. The porosity in the (C16)-terminated and the poly(epsilon-caprolactone(s)) was impossible to eliminate by applying a high external pressure during crystallization. A collective view of all the results obtained confirm that the transport properties are primarily controlled by the hydroxyl group concentration.
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| 14. |
- Hedenqvist, Mikael S., et al.
(författare)
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Two-stage sorption in rubbery semicrystalline polymers : transport of primary alcohols in polyesteramide
- 2002
-
Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 43:10, s. 3061-3068
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Tidskriftsartikel (refereegranskat)abstract
- This paper deals with the two-stage sorption of methanol, 1-propanol and I-hexanol in a rubbery semicrystalline polyesteramide. This is the first time two-stage sorption is reported for a semicrystalline rubbery polymer. Mass uptake, specimen geometry and surface concentration were measured independently. The two-stage sorption curve describes two overlapping processes; a very rapid diffusion (mode 1) superimposed onto a normal s-shaped sorption curve (mode 2). Mode I swelling was uni-dimensional and mode 2 swelling was initially uni-dimensional and later three-dimensional. It was possible to model the sorption curves by assuming time-dependent solute-surface-concentration conditions, similar to those used to describe simple s-shaped sorption. The obtained time dependence, characterised by a single relaxation time, agreed with experimental values of the surface concentration obtained by infrared spectroscopy. The relaxation time increased exponentially with increasing size of the diffusing alcohol molecule. The solubility of the alcohols in the polymer increased with increasing hydroxyl-group density. The diffusivity of alcohol decreased nonlinearly with increasing length of the molecule, size effects being less important for larger solutes.
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| 15. |
- Hillborg, H., et al.
(författare)
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Characterisation of low molar mass siloxanes extracted from crosslinked polydimethylsiloxanes exposed to corona discharges
- 2001
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Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 42:21, s. 8883-8889
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Tidskriftsartikel (refereegranskat)abstract
- Crosslinked polydimethylsiloxanes were exposed to corona discharges in dry air at normal pressure. Short-time solvent extraction and subsequent analysis of the extractables, by gas chromatography, mass spectrometry and size exclusion chromatography showed that, oligomers consisting mainly of cyclics with 4-9 repeating units were formed during corona exposure. The size distribution of the oligomers was independent of the crosslink density and corona exposure time. The amount of oligomers located at the surface increased, with increasing storage time, after the corona exposure in qualitative agreement with the ongoing hydrophobic recovery process. Longer extractions penetrated deeper into the samples, and, in addition to the cyclic oligomers, higher molar mass species (similar to 50,000 g mol(-1) for unexposed samples) were detected. Samples exposed to corona, treated in this way, showed a broadening of the high molar mass peak towards lower molar masses.
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| 16. |
- Hillborg, H., et al.
(författare)
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Crosslinked polydimethylsiloxane exposed to oxygen plasma studied by neutron reflectometry and other surface specific techniques
- 2000
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Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 41:18, s. 6851-6863
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Tidskriftsartikel (refereegranskat)abstract
- Spin-coated specimens of crosslinked polydimethylsiloxane (PDMS) exposed to radio-frequency (RF) and microwave (MW) oxygen plasma were studied by specular neutron reflectometry, X-ray photoelectron spectroscopy (XPS), Wilhelmy balance, contact angle measurements, scanning electron microscopy and atomic force microscopy. Neutron reflectometry and XPS showed that the oxygen plasma led to the formation of a smooth (<10 nm), oxidised surface layer with a thickness of 130-160 nm. The oxidised layer contained a mixture of the original polymer and silicon bonded to three or four oxygen atoms (SiOx). The oxidised layer was thinner after longer plasma exposure, indicating a decrease in specific volume due to a conversion of the polymer structure to an inorganic SiOx-rich structure. The formation of the SiOx-containing layer with low segmental mobility was further confirmed by the small hysteresis in the Wilhelmy balance measurements. The similarity in the hydrophobicity recovery kinetics of specimens aged in dry air, dry argon and vacuum and XPS data showed that the hydrophobicity recovery is not due to contamination through adsorption from the atmosphere but due to migration of low molar mass PDMS species to the surface. Scanning electron microscopy also showed the presence of surface cracks in heavily oxidised specimens.
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| 17. |
- Hillborg, H., et al.
(författare)
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Hydrophobic recovery of polydimethylsiloxane after exposure to partial discharges as a function of crosslink density
- 2001
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Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 42:17, s. 7349-7362
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Tidskriftsartikel (refereegranskat)abstract
- Polydimethylsiloxanes with different crosslink densities were exposed to corona discharges or GHz air plasma and studied by contact angle measurements, X-ray photoelectron spectroscopy, optical microscopy, scanning electron microscopy and atomic force microscopy. The degree of surface oxidation increased with increasing exposure time with a limiting depth of 100-150 nm. Surface oxidation was faster in more highly crosslinked polymers. Within the oxidised layer, a brittle, microporous silica-like layer with a minimum organic silicone content of 40% gradually developed with increasing exposure time. The strain at which the silica-like layer cracked decreased with increasing dose of corona or air plasma. The hydrophobic recovery following the corona/air plasma exposure occurred at a slow rate by diffusion of oligomers through the microporous but uncracked silica-like layer or at a much higher rate by transport of oligomers through cracks in the silica-like layer.
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| 18. |
- Hong, Y., et al.
(författare)
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Film blowing of linear low-density polyethylene blended with a novel hyperbranched polymer processing aid
- 2000
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Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 41:21, s. 7705-7713
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Tidskriftsartikel (refereegranskat)abstract
- The use of hyperbranched polymer (HBP) as a processing aid for linear low-density polyethylene (LLDPE) in the tubular film blowing process was investigated. Through the addition of HBP, sharkskin was successfully eliminated without significantly changing the overall physical properties of LLDPE films. Also, there was a minimum of 40% enhancement in processing rate with addition of 0.5 wt% HBP. The study showed that HBP and LLDPE are immiscible, and HBP has a tendency to migrate to the surface, subsequently, it seems to form a lubricating layer between the metal surfaces and the bulk material. This phase separation between HBP and LLDPE results in an HBP-rich surface, which has a high potential to create unique surface properties tailored to various applications. Rheological analysis indicated that excessive slip was present in HBP/LLDPE suggesting that the onset of slip is not the cause of sharkskin. On the contrary, it may be partially responsible for the elimination of sharkskin.
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| 19. |
- Jacobsson, Per, et al.
(författare)
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Ion association effects and phase separation in poly(propylene oxide) modified poly(dimethylsiloxane) complexed with triflate salts
- 1992
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Ingår i: Polymer. - : Elsevier. - 0032-3861 .- 1873-2291. ; 33:13, s. 2778-2783
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Tidskriftsartikel (refereegranskat)abstract
- Phase separation is observed in poly(propylene oxide) modified poly(dimethylsiloxane) (PPO-PDMS) with excess poly(propylene oxide) (PPO) when salts of MCF3SO3 (M = Li, Na) are added. The same behaviour is inferred for KCF3SO3. The solutions above and below the boundary layer have been studied by Raman spectroscopy and in particular by examining the non-degenerate, symmetric stretch (A1, SO3) Raman mode of the CF3SO3− anion. The upper part is siloxane rich; salt is present on both sides of the boundary layer with a much lower concentration in the upper part. The formation of the boundary layer is attributed to an increasing difference in surface tension between the PPO/salt/PPO-PDMS complexes and the separate PPO, PPO-PDMS components. The boundary layer moves up with increase in concentration. The number of ‘free’ ions decreases and ion association increases with increase in temperature. There is evidence of contact ion pairs, triplets and aggregates. Values of conductivity are quoted for 293 K.
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| 20. |
- Kornmann, X., et al.
(författare)
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Synthesis of epoxy-clay nanocomposites : influence of the nature of the clay on structure
- 2001
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Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 42:4, s. 1303-1310
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Tidskriftsartikel (refereegranskat)abstract
- Epoxy-clay nanocomposites were synthesised using two montmorillonite clays (MMT) with different cation-exchange capacities (CEC) (94 and 140 meg/100 g). The purpose was to investigate the influence of the CEC of the clay on the synthesis and structure of epoxy-clay nanocomposites. The dispersion of the 1 nm thick clay layers was investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Although XRD data did not show any apparent order of the clay layers in the nanocomposite, TEM revealed parallel clay layers with interlamellar spacing of 90 Angstrom (MMT of high CEC) and 110 Angstrom (MMT of lower CEC) and the presence of remnant multiplets of non-exfoliated layers. A mechanism responsible for the influence of CEC on nanocomposite interlamellar spacing is discussed. The dispersion of the clay was investigated by SEM and found to be finer in the nanocomposites as compared with in conventional composites although the nanocomposites still have clay aggregates at the microscale rather than a monolithic structure.
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| 21. |
- Kornmann, X., et al.
(författare)
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Synthesis of epoxy-clay nanocomposites. Influence of the nature of the curing agent on structure
- 2001
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Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 42:10, s. 4493-4499
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Tidskriftsartikel (refereegranskat)abstract
- Epoxy-clay nanocomposites were synthesised by swelling an organophilic montmorillonite in a diglycidyl ether of bisphenol A resin with subsequent polymerisation. Three different curing agents were used: an aliphatic diamine and two cycloaliphatic diamines. The cure kinetics of these systems was evaluated by differential scanning calorimetry and the structure of the nanocomposites was characterised by X-ray diffraction and transmission electron microscopy. Successful nanocomposite synthesis was dependent not only on the cure kinetics of the epoxy system but also on the rate of diffusion of the curing agent into the galleries because it affects the intragallery cure kinetics. The nature of the curing agent influences these two phenomena substantially and therefore the resulting structure of the nanocomposite. The curing temperature controls the balance between the extragallery reaction rate of the epoxy system and the diffusion rate of the curing agent into the galleries. Thus, the choice of curing agent and curing conditions controls the extent of exfoliation of the clay in the material.
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| 22. |
- Kornmann, X., et al.
(författare)
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Synthesis of epoxy–clay nanocomposites. Influence of the nature of the curing agent on structure
- 2001
-
Ingår i: Polymer. - : Elsevier BV. - 0032-3861 .- 1873-2291. ; 42:10, s. 4493-4499
-
Tidskriftsartikel (refereegranskat)abstract
- Epoxy-clay nanocomposites were synthesised by swelling an organophilic montmorillonite in a diglycidyl ether of bisphenol A resin with subsequent polymerisation. Three different curing agents were used: an aliphatic diamine and two cycloaliphatic diamines. The cure kinetics of these systems was evaluated by differential scanning calorimetry and the structure of the nanocomposites was characterised by X-ray diffraction and transmission electron microscopy. Successful nanocomposite synthesis was dependent not only on the cure kinetics of the epoxy system but also on the rate of diffusion of the curing agent into the galleries because it affects the intragallery cure kinetics. The nature of the curing agent influences these two phenomena substantially and therefore the resulting structure of the nanocomposite. The curing temperature controls the balance between the extragallery reaction rate of the epoxy system and the diffusion rate of the curing agent into the galleries. Thus, the choice of curing agent and curing conditions controls the extent of exfoliation of the clay in the material.
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| 23. |
- Laihonen, Sari J., et al.
(författare)
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Crystal structure and morphology of melt-crystallized poly(propylene-stat-ethylene) fractions.
- 1997
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Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 38:2, s. 371-377
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Tidskriftsartikel (refereegranskat)abstract
- Crystallinity, crystal structure and lamellar thickness in melt-crystallized samples of poly(propylene-stat-ethylene) fractions with 2.7–11.0 mol% ethylene comonomer and of approximately constant tacticity were assessed by wide- and small-angle X-ray scattering, differential scanning calorimetry and infra-red spectroscopy. Most of the samples were crystallized under isothermal conditions at 373 K. In comparison with an isotactic homopolymer of polypropylene, the copolymers showed lower crystallinity, melting enthalpy and average length of 3/1 helices, a slightly larger unit cell, a longer long period and an invariant lamellar thickness. The X-ray crystallinity of the copolymers remained approximately constant with increasing ethylene content, whereas the γ-crystallinity increased and the heat of fusion decreased moderately. It is suggested that the ethylene units are partially included in the crystals, and that this causes the invariance in crystallinity and crystal thickness. The observed gradual decrease in average 3/1 helix length with increasing ethylene content as assessed by infra-red spectroscopy is in accordance with this suggestion.
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| 24. |
- Laihonen, Sari J., et al.
(författare)
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Crystallization kinetics and morphology of poly(propylene-stat-ethylene) fractions.
- 1997
-
Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 38:2, s. 361-369
-
Tidskriftsartikel (refereegranskat)abstract
- The crystallization and melting behaviour and the morphology of fractions of poly(propylene-stat-ethylene) with 2.7–11.0 mol% ethylene were studied by differential scanning calorimetry, wide-angle X-ray scattering, polarized light microscopy and transmission electron microscopy, after etching with permanganic acid. The inclusion of ethylene co-repeating units in isotactic polypropylene (0–11.0 mol% ethylene) caused approximately linear decreases in kinetic and equilibrium melting temperatures and in the glass transition temperature with increasing ethylene content. X-ray scattering showed that the content of the γ form increased with increasing ethylene content, increasing crystallization temperature and decreasing cooling rate from the molten state. It was shown for one of the copolymers (8.7 mol% ethylene) that during heating approximately 50% of the γ form was converted to the α form before the final melting of the sample. The rest of the γ crystals melted without transformation to the α form. The multimodality of the crystal melting above the crystallization temperature in the polymers with a more uniform crystal structure was caused by recrystallization during heating, whereas polymers with appreciable contents of both α and γ forms exhibited multimodal melting at all the heating rates adopted. The size of the low temperature melting peak as assessed at a heating rate of 40 K min−1 was approximately proportional to the initial content of the γ form. By comparison with the spherulitic structure of homopolymers, that of the copolymers was coarser with internal and peripheral pockets of molten material during spherulite growth. The crystal lamellae exhibited more curvature in the copolymer samples than in the homopolymer.
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| 25. |
- Lange, J., et al.
(författare)
-
Barrier coatings for flexible packaging based on hyperbranched resins
- 2001
-
Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 42:17, s. 7403-7410
-
Tidskriftsartikel (refereegranskat)abstract
- Hyperbranched resins have been evaluated for use as barrier coatings. Different types of modified hydroxy-functional hyperbranched polyester resins were prepared and partially end-capped with acrylate or methacrylate units. Crystalline end-groups (poly(epsilon -caprolactone) were grafted onto some resins. The coatings were applied on poly(ethylene terephthalate) and polypropylene substrates and crosslinked by UV light and their barrier against oxygen and water vapour determined. The results show that hyperbranched coatings give a pronounced improvement in oxygen barrier on both substrates. Expressed in terms of oxygen permeability coefficient, the improvement was a factor of up to 60 times compared to polypropylene and up to 2.2 times compared to poly(ethylene terephthalate). As for other hydroxy-functional barrier polymers, the amount of hydroxyl groups in the hyperbranched resins was found to play a major role concerning the oxygen barrier, controlling both performance and water sensitivity. It was seen that humidity led to a decrease in barrier at the highest hydroxyl group concentration, whereas the barrier performance of coatings with lower concentration of hydroxyl groups instead improved under humid conditions. It was also found that crystalline end-groups did not improve the oxygen barrier and that none of the synthesised resins gave any improvement in water vapour barrier.
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| 26. |
- Lange, J, et al.
(författare)
-
Gelation behaviour during chainwise crosslinking polymerisation of methacrylate resins
- 1999
-
Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 40, s. 5699-5707
-
Tidskriftsartikel (refereegranskat)abstract
- The gelation process in chainwise crosslinking polymerisation of methacrylate resins with average functionalities of 2.1-50 (1.05-25 methacrylate groups/molecule) was investigated using dynamic mechanical analysis. For all systems a crossover in tan delta (tan delta independent of frequency) was observed at gelation. The gel time was found to decrease with increasing functionality of the system. Within the measured frequency ranges, power law behaviour for the dynamic modulus was observed at the gel point in all systems. A value of the power law exponent n of 0.4 +/- 0.2 to 0.6 +/- 0.1 (increasing with increasing functionality of the system) was determined for gelation during reactions at T greater than or equal to T-g infinity. This trend suggests that the differences in screening between the systems dominate over the difference in fractal dimension. For reaction temperatures below T-g infinity a value of n = 0.3 +/- 01 was obtained, which was attributed to the influence of micro-vitrification. (C) 1999 Elsevier Science Ltd. All rights reserved.
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| 27. |
- Lindberg, T., et al.
(författare)
-
Graft polymerisation of acrylamide onto PCL film by electron beam pre-irradiation in air or argon. Morphology in the final grafted state
- 2000
-
Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 41:11, s. 4099-4111
-
Tidskriftsartikel (refereegranskat)abstract
- Poly(epsilon-caprolactone) has been graft polymerised to final graft yields with acrylamide (AAm) as monomer in an aqueous solution by the pre-irradiation method. The synthesis of the samples obtained, pre-irradiated in air or argon atmosphere, was controlled by dose and concentration of inhibitor, provided as Mohr's salt, in the ranges from 2.5 to 10 Mrad and from 0.005 to 0.500 wt%, respectively. Final graft yields and lateral dimensions in swollen condition ranged from 70 to 3400 wt%, and from 23 x 30 to 89 x 94 mm(2), respectively, as atmosphere during irradiation, dose and concentration of inhibitor were altered. These properties gave values in crystallinity extending from 4 to 57 wt%. Samples pre-irradiated in air and subsequently graft polymerised yielded higher values of crystallinity in the entire range of dose and concentration of inhibitor. At low concentration of inhibitor, final graft yield and lateral dimension for samples pre-irradiated in air had considerably larger values while the final graft yield and lateral dimension of samples pre-irradiated in argon had slightly larger values at high concentration of inhibitor. The initial biaxial morphology of the PCL film was continuously transformed into a uniform morphology, which was reached at a final graft yield of approximately 800 wt%.
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| 28. |
- Liu, X. H., et al.
(författare)
-
Polyamide 6-clay nanocompositles/polypropylene-grafted-maleic anhydride alloys
- 2001
-
Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 42:19, s. 8235-8239
-
Tidskriftsartikel (refereegranskat)abstract
- Polyamide 6-clay nanocomposites (PA6CN) based on montmorillonite typically show some brittleness with clay addition. In order to address this problem, PA6CN/PP-g-MAH alloys were prepared through blending PA6CN with polypropylene-grafted-maleic anhydride (PP-g-MAH). The mechanical properties, dynamic mechanical temperature spectra, morphology and water absorption of the alloys were studied. Compared with PA6CN, the notched impact strength of the alloys increased greatly while the alloys still maintained higher stiffness and strength than that of PA 6. The morphological studies via scanning electron microscopy (SEM) showed a PP-g-MAH toughen phase dispersed in PA6CN matrix. As the PP-g-MAH content was increased, reduced water absorption was observed.
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| 29. |
- Liu, X. H., et al.
(författare)
-
Polymorphism in polyamide 66/clay nanocomposites
- 2002
-
Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 43:18, s. 4967-4972
-
Tidskriftsartikel (refereegranskat)abstract
- Polyamide 66/clay nanocomposites (PA66CN) were prepared via melt compounding method by using a new kind of organophilic clay, which was obtained through co-intercalation of epoxy resin and quaternary ammonium into Na-montmorillorlite. The silicate layers were dispersed homogeneously and nearly exfoliated in polyamide 66 (PA66) matrix. The introduction of silicate layers induced the appearance of the gamma phase in PA66CN at room temperature, more clay loadings would amplify this phenomenon; the addition of clay also changed the structure of the a crystalline phase. The presence of silicate layers increased the crystallization rate and had a strong hetero phase nucleation effect on PA66 matrix. The lower Brill transition temperature of PA66CN can be attributed to the strong interaction between polyamide chains and surfaces of silicate layers.
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| 30. |
- Liu, Xiaohui, et al.
(författare)
-
Phase transition in nylon 6/clay nanocomposites on annealing
- 2002
-
Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 43:6, s. 1933-1936
-
Tidskriftsartikel (refereegranskat)abstract
- The γ -> α crystalline phase transition in nylon 6/clay nanocomposite prior to melting was investigated by X-ray diffraction. The phase transition in the nanocomposite took place at 160 °C, 40 °C higher than that of nylon 6 at 120 °C. The transition extent in the nanocomposite was lower than that in nylon 6. This could be caused by the strongly confined spaces between layers, and the favorable environment for the formation of the γ phase in the existence of clay. Besides, the less grown crystallites of the α phase transformed from the γ phase in the nanocomposite began to melt at much lower temperature than its normal melting temperature
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| 31. |
- Liu, Xiaohui, et al.
(författare)
-
PP/clay nanocomposites prepared by grafting-melt intercalation
- 2001
-
Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 42:25, s. 10013-10019
-
Tidskriftsartikel (refereegranskat)abstract
- Polypropylene (PP)/clay nanocomposites (PPCN) were prepared via grafting-melt compounding by using a new kind of co-intercalation organophilic clay which had a larger interlayer spacing than the ordinarily organophilic clay only modified by alkyl ammonium. One of the co-intercalation monomers was unsaturated so it could tether on the PP backbone by virtue of a grafting reaction. The larger interlayer spacing and strong interaction caused by grafting can improve the dispersion effect of silicate layers in the PP matrix, which was confirmed by X-ray diffraction (XRD) and transmission electron microscopy (TEM). The mechanical properties of PPCN were improved with the addition of clay. The incorporation of silicate layers also gave rise to a considerable increase of the storage modulus (stiffness) and a decrease of the tan δ value, demonstrating the reinforcing effect of clay on the PP matrix. Besides, the glass transition temperature (Tg) of PPCN decreased in the presence of the silicate layers. The addition of clay did not change the crystal structure of PP, however silicate layers acted as nucleating agents for the crystallization of PP.
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| 32. |
- Magnusson, Helene, et al.
(författare)
-
The effect of degree of branching on the rheological and thermal properties of hyperbranched aliphatic polyethers
- 2002
-
Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 43:2, s. 301-306
-
Tidskriftsartikel (refereegranskat)abstract
- A series of hyperbranched aliphatic polyethers with different degree of branching (DB) and molecular weights have been studied with respect to their rheological and thermal properties. The DB was shown to affect the ability of the polymers to crystallize and thereby also the rheological properties of the polymers. A low DB resulted in semi-crystalline polymers with melting points between 100 and 130 degreesC. The polymers with a higher DB were essentially amorphous and behaved as non-entangled Newtonian liquids in the molten state.
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| 33. |
- Marklund, E., et al.
(författare)
-
Properties of polyketone/polypropylene blends
- 2001
-
Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 42:7, s. 3153-3160
-
Tidskriftsartikel (refereegranskat)abstract
- Blends of polypropylene and two polyketone grades with low and medium-high viscosities were prepared by melt extrusion. To obtain good compatibility, a maleic-anhydride-polypropylene copolymer was added to the blends. Polyoxypropylenediamine was added to some of the blends to further enhance compatibility. The blends were analysed with differential scanning calorimetry. In a second step, the blends were compression or injection moulded. Scanning electron microscopy, shear viscosity, density measurements and infrared spectroscopy were used to characterise the moulded blends and their oxygen permeabilities were assessed. Impact strength and hardness were measured on injection-moulded blends. It was shown that the oxygen barrier properties of polypropylene could be greatly enhanced by a small addition of primarily the low-viscosity polyketone. A content of 23.9% by volume of polyketone was sufficient to lower the permeability by 70% compared to pure polypropylene. This was because a polyketone-rich surface layer was formed during compression moulding. The incorporation of polyoxypropylenediamine had a profound effect on the morphology. The polyketone particles in this case were very small, and the absence of pull-outs suggested an enhanced phase adhesion between the different components. Further, the incorporation of polyoxypropylenediamine had no impact on the oxygen permeability but the impact roughness and hardness were increased and the shear viscosity was also increased in its presence. This indicated that chemical bonds were formed between polyketone, polyoxypropylenediamine and the maleic-anhydride-polypropylene copolymer. This network suppressed crystallisation of primarily the polyketone component.
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| 34. |
- Mathew, Aji P., et al.
(författare)
-
Transport of styrene monomer through natural rubber
- 1995
-
Ingår i: Polymer. - : Elsevier BV. - 0032-3861 .- 1873-2291. ; 36:26, s. 4935-4942
-
Tidskriftsartikel (refereegranskat)abstract
- The diffusion and transport of inhibitor-free styrene through crosslinked natural rubber (NR) have been studied at various temperatures. NR has been vulcanized by conventional, efficient, peroxide and mixed vulcanization techniques. The dependence of diffusion coefficient on the crosslinking system has been studied for all the systems. The influence of temperature on the sorption and the activation energies of sorption have been calculated. The interaction parameter, permeability, sorption coefficient and molecular weight between crosslinks have been evaluated using the diffusion data. The effect of degree of crosslinking on the sorption characteristics of styrene through NR has also been investigated for the different crosslinking systems. The peroxide system showed lowest uptake and the conventional system showed highest uptake.
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| 35. |
- Moilanen, A.M., et al.
(författare)
-
FTIR and strengthening studies on liquid crystalline oligomers of 2-thioalkoxy/2-alkoxyhydroquinones and terephthaloyl chloride
- 2000
-
Ingår i: Polymer. - : Elsevier Science Ltd, Exeter, United Kingdom. - 0032-3861 .- 1873-2291. ; 41:20, s. 7297-7302
-
Tidskriftsartikel (refereegranskat)abstract
- The properties of liquid crystalline (LC) oligomers produced from 2-thioalkoxyhydroquinones (2-thioalkoxyHQs) and 2-alkoxyhydroquinones (2-alkoxyHQs) with terephthaloyl chloride (1a-c, 2a-c) have been studied and their compatibility with polyamide 11 (PA 11) has been investigated. FTIR studies showed two conformations of the synthesized oligomers. A three-point bending test indicated that oligomeric chains could strengthen the final flexural properties of the polyamide. Strength of PA 11 was increased by addition of only 1% of LC oligomers to the matrix. Compatibility between oligomer chains and PA 11 was lower than the compatibility between corresponding oligomers of 2-alkoxy-4-hydroxybenzoic acids (2-alkoxyHBAs) and PA 11. (C) 2000 Elsevier Science Ltd. All rights reserved.The properties of liquid crystalline (LC) oligomers produced from 2-thioalkoxyhydroquinones (2-thioalkoxyHQs) and 2-alkoxyhydroquinones (2-alkoxyHQs) with terephthaloyl chloride (1a-c, 2a-c) have been studied and their compatibility with polyamide 11 (PA 11) has been investigated. FTIR studies showed two conformations of the synthesized oligomers. A three-point bending test indicated that oligomeric chains could strengthen the final flexural properties of the polyamide. Strength of PA 11 was increased by addition of only 1% of LC oligomers to the matrix. Compatibility between oligomer chains and PA 11 was lower than the compatibility between corresponding oligomers of 2-alkoxy-4-hydroxybenzoic acids (2-alkoxyHBAs) and PA 11.
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| 36. |
- Molochnikov, L. S., et al.
(författare)
-
Coordination of Cu(II) and Ni(II) in polymers imprinted so as to optimize amine chelate formation
- 2003
-
Ingår i: Polymer. - : Elsevier BV. - 0032-3861 .- 1873-2291. ; 44:17, s. 4805-4815
-
Tidskriftsartikel (refereegranskat)abstract
- Molecular imprinting has become an established technique. However, little was done on direct investigation of the sorbents produced. In the present work, en ESR method was used for the investigation of the complex formation processes within the sorbents imprinted with copper(II) and nickel(II). The sorbents were synthesized from a mixture of linear low molecular weight polyethyleneimine oligomers. The composition, structure and distribution of complexes in the resin phase were investigated. The effects of the synthesis conditions, loading degree and water content were examined. The presence of certain copper complexes was found to be a convenient characteristic of the imprinting efficiency. The optimum synthesis conditions for obtaining sorbents imprinted with copper(II) or nickel(II) were identified. The imprinting results in the improvement of the stability of the complexes and the selectivity and working capacity of the sorbents. The imprinted samples are also characterized by a more even distribution of chelating sites. The synthesis conditions and loading by ions allow for the regulation of the ratio between individual complexes and magnetic associates in the resin phase. This is a critical point on the future use of the metal containing imprinted sorbents as catalysts.
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| 37. |
- Neway, B., et al.
(författare)
-
Effect of thermal history on free volume and transport properties of high molar mass polyethylene
- 2003
-
Ingår i: Polymer. - : Elsevier BV. - 0032-3861 .- 1873-2291. ; 44:14, s. 4003-4009
-
Tidskriftsartikel (refereegranskat)abstract
- The desorption of n-hexane from high molar mass polyethylene at 298 K has been studied. The polymer was given different thermal treatments to obtain differences in crystallinity, morphology and composition of the non-crystalline fraction. Crystal contents determined by Raman spectroscopy were always lower than those determined by density measurements. The systems with high crystallinity showed in relative terms a low content of interfacial component. The n-hexane solubilities of the samples were strictly proportional to the volume fraction of penetrable polymer (liquid-like and interfacial components) and the solubility was low in comparison with that of branched polyethylene of the same crystallinity. The Cohen-Tumbull-Fujita free volume theory was numerically capable of describing the desorption process in the polyethylenes studied. One of the methods used assumed that all three non-crystalline components-liquid-like, interfacial liquid-like and interfacial crystal core components-are penetrable by n-hexane and this method yielded data for the geometrical impedance factor and the fractional free volume with physically realistic trends, but the changes in the geometrical impedance factor was not in quantitative agreement with the Fricke model applied to the morphological data. This lack of numerical agreement is tentatively due to the fact that the assessment of crystal shape by transmission electron microscopy of stained sections systematically underestimates the crystal widths, particularly for the low-crystallinity samples with curved and 'twisting' crystal lamellae.
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| 38. |
- Neway, B., et al.
(författare)
-
Free volume and transport properties of heterogeneous poly(ethylene-co-octene)s
- 2001
-
Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 42:12, s. 5307-5319
-
Tidskriftsartikel (refereegranskat)abstract
- n-Hexane desorption measurements were pet-formed on heterogeneous poly(ethylene-co-octene)s with hexyl branch contents between 0.8 and 3.9 mol% and crystallinities between 30 and 60%, Crystal core contents obtained by Raman spectroscopy were lower than the density-based crystallinity, particularly For the samples with the highest degree of branching. A modified Cohen-Tumbull-Fujita free volume model adequately described the diffusivity data. The free volume of the penetrable phases was strongly dependent on their total volume fraction, suggesting the presence of an interfacial penetrable component with low fractional free volume. The dependence of the fractional free volume of the penetrable phases on the phase composition suggests that mass transport takes place from the liquid-like component to the interfacial component and that the penetrant molecules are trapped at the interfacial sites. The decrease in geometrical impedance factor with increasing crystallinity may be explained by the presence of extraordinarily wide dominant crystal lamellae in the heterogeneous low crystallinity samples. The saturation concentration of n-hexane in a wide range of polyethylenes (including the heterogeneous poly(ethylene-co-octene)s, linear polyethylenes and poly(ethylene-co-butene)s reported earlier; crystallinity range: 30-94%) showed a complex non-linear dependence on crystallinity that was qualitative in accordance with rubber elasticity theory considering also molecular cilia.
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| 39. |
- Ohrlander, M., et al.
(författare)
-
The effect of electron beam irradiation on PCL and PDXO-X monitored by luminescence and electron spin resonance measurements
- 2000
-
Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 41:4, s. 1277-1286
-
Tidskriftsartikel (refereegranskat)abstract
- The effect of electron beam irradiation in air or argon was studied on two hydrolysable aliphatic polyesters, poly(e-caprolactone) (PCL) and chemically cross-linked poly(1,5-dioxepan-2-one) (PDXO-X). A secondary alkylether radical and a tertiary alkyl radical were identified by ESR in PCL and PDXO-X after irradiation in both air and argon. For the samples irradiated in air, peroxy radicals were detected in PCL but not in PDXO-X. For irradiated PCL, the intensities in the luminescence measurements seemed to be dose-dependent. Large amounts of oxidation products were found present in the PDXO-X irradiated in air and the luminescence intensities seemed to be dose-dependent.The effect of electron beam irradiation in air or argon was studied on two hydrolysable aliphatic polyesters, poly(e-caprolactone) (PCL) and chemically cross-linked poly(1,5-dioxepan-2-one) (PDXO-X). A secondary alkylether radical and tertiary alkyl radical were identified by ESR in PCL and PDXO-X after irradiation in both air and argon. For the samples irradiated in air, peroxy radicals were detected in PCL but not in PDXO-X. For irradiated PCL, the intensities in the luminescence measurements seemed to be dose-dependent. Large amounts of oxidation products were found present in the PDXO-X irradiated in air and the luminescence intensities seemed to be dose-dependent.
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| 40. |
- Olabarrieta, Idoia, et al.
(författare)
-
Transport properties of chitosan and whey blended with poly(ε-caprolactone) assessed by standard permeability measurements and microcalorimetry
- 2001
-
Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 42:9, s. 4401-4408
-
Tidskriftsartikel (refereegranskat)abstract
- Blends of poly(p-caprolactone) (PCL) with chitosan and a whey-protein-isolate (WPI) were prepared by solution mixing and film casting. The purpose was to increase the water vapour resistivity of chitosan and whey by blending them with a hydrophobic biodegradable polymer. The water vapour transmission rate was determined by a standard technique and by a new technique based on microcalorimetry. The blends were characterised by scanning electron microscopy (SEM), density measurements and thermogravimetry. Oxygen permeability was measured on the pure components and on some of the blends. The incorporation of PCL yielded a pronounced decrease in water vapour transmission rate of both chitosan and the WPI measured at a relative humidity gradient of 11 to 0%. A volume content of 17-18% of PCL lowered the water vapour transmission rate by 70-90%. It was found that the majority of the PCL particles were ellipsoidal in chitosan and fibrous in the WPI and the data indicated that the particle shape had an important influence on the water vapour transmission rate. The large decrease in water vapour transmission rate was also due to a reduction in water solubility because of limited swelling of the constrained chitosan or WPI matrix in the presence of PCL. SEM revealed that the miscibility/compatibility between PCL and the matrices was good. The water vapour transmission rate of the films decreased with increasing vacuum-drying time of the chitosan and WPI solutions. Microcalorimetry provided accurate estimates of water vapour transmission rate. Furthermore. this technique proved to be very flexible and the water vapour transmission rate could be determined over a broad range of relative humidities in a single experiment.
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| 41. |
- Ortegren, J., et al.
(författare)
-
Dielectric relaxation of liquid crystalline dendrimers and liquid crystalline polymers with pendant nitro groups
- 2001
-
Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 42:25, s. 10027-10033
-
Tidskriftsartikel (refereegranskat)abstract
- The dielectric relaxation was determined in a time-domain spectrometer between 100 and 295 K and from 0.1 to 1000 Hz for series of dendritic liquid crystalline polymers with scaffolds based on 2,2-bis(hydroxymethyl)propionic acid (bis-MPA) of generations 0-3 with 4-((R)-1-methylheptyloxy)phenyl 4-{4'-[10-(hydroxy-carbonyl)decyloxy]-phenyl} benzoate as mesogen and for the second generation of dendrimers with 4-[10-(hydroxycarbonyl)decyloxy]-biphenyl 4-[4'-(2-(R)-octyloxy)-3-nitrophenyl] benzoate as mesogen. Dielectric data are also reported for a side-chain liquid crystalline polymer based on {4''-[(R)-(-)-2-octyloxyl-3-nitro-phenyl 4-(4'-(11-acryloyl-oxyundecyloxy)phenyl}benzoate. The low temperature subglass process (gamma) assigned to the spacer group was essentially insensitive to molecular architecture and to the presence of a pendant nitro group in the mesogen. The high temperature sub-glass process (beta) assigned to a 180 degrees flip of part of mesogen was only moderately sensitive to the molecular architecture. The introduction of a pendant nitro group in the mesogen led to a substantial increase in both activation energy and relaxation strength. The results suggest that the phenylene ring with the pendant nitro group participates in the beta process.
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| 42. |
- Qu, X., et al.
(författare)
-
Effect of lactic/glycolic acid side chains on the thermal degradation kinetics of chitosan derivatives
- 2000
-
Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 41:13, s. 4841-4847
-
Tidskriftsartikel (refereegranskat)abstract
- The thermal degradation properties of chitosan and lactic and/or glycolic acid grafted chitosan have been studied by differential scanning calorimetry (DSC) and thermogravimetric analyses (TG) in the range of 25-500 degrees C. Both DSC and dynamic TG results show that the samples are thermal degraded easily after grafting the lactic and/or glycolic acid. From the isothermal TG experiments, the initial activation energy and the activation energy at different stages is obtained. The initial activation energy of all grafted samples is much lower than that of chitosan, especially for the sample GA/CS = 2 and it varies with degree of conversion. The FT-IR spectra of thermally degraded residues give an indication of the chitosan polyscaccharide ring degradation after 30 min in 280 degrees C, while sample GA/CS = 2 will degrade only after 15 min.
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| 43. |
- Qu, X., et al.
(författare)
-
Novel pH-sensitive chitosan hydrogels : swelling behavior and states of water
- 2000
-
Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 41:12, s. 4589-4598
-
Tidskriftsartikel (refereegranskat)abstract
- Physically crosslinked chitosan hydrogels were synthesized by grafting D,L-lactic acid (LA) and/or glycolic acid (GA) with different feed ratios. The physical crosslinking was formed due to the hydrophobic side chains aggregation and intermolecular interactions through hydrogen bonds between side and main chains. The crystallinity of original chitosan decreased by grafting LA and GA. The structural change of the hydrogels in different pH buffers was characterized by FT-IR method and the results were interpreted. Differential scanning calorimetry (DSC) was used to probe the states of water in the chitosan hydrogels. Three types of water were found in the samples, i.e. freezing water (namely free water), non-freezing water (namely bound water), and freezing bound water, while there are variations in the amount of bound water for different hydrogels. The effect of hydrophobic side chains on water state and swelling behavior were discussed.
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| 44. |
- Schauer, E., et al.
(författare)
-
Morphological variations in PMMA-modified epoxy mixtures by PEO addition
- 2002
-
Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 43:4, s. 1241-1248
-
Tidskriftsartikel (refereegranskat)abstract
- Thermoplastic epoxy blends are successfully used commercially. The thermoplastic may serve as a toughening agent although other properties may also be improved. In the present study, microscopy and mechanical testing techniques were used to study morphology and ultimate properties of ternary epoxy/Poly(methyl methacrylate) (PMMA)-Poly(ethylene oxide) (PEO) blends. PEO is functioning like a compatibilizer by which the morphology of the resulting polymer mixture may be changed dramatically by only small amounts of PEO. Whilst stiffness was controled by the corresponding matrix of the ternary mixture, both strength and fracture toughness were a function of the defined morphology. However, the most efficient toughening agent was PMMA, in particular when present as a co-continuous PMMA-rich phase within the epoxy-rich matrix.
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| 45. |
- Stridsberg, K., et al.
(författare)
-
Changes in chemical and thermal properties of the tri-block copolymer poly(L-lactide-b-1,5-dioxepan-2-one-b-L-lactide) during hydrolytic degradation
- 2000
-
Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 41:20, s. 7321-7330
-
Tidskriftsartikel (refereegranskat)abstract
- Hydrolysis of the novel tri-block copolymer poly(L-lactide-b-1,5-dioxepan-2-one-b-L-lactide) of different compositions has been studied in buffered salt solution at 37 degrees C and pH 7.4. Specifically, polymer weight loss, composition changes, molecular weight changes, thermal properties and release of lactic acid and 3-(2-hydroxyethyl)-propanoic acid have been detected. The degradation was found to start immediately after the sample was immersed into the aqueous buffer solution. The rate of degradation was influenced only by the original molecular weight, the copolymer composition had no significant effect. The heat of fusion and Tg increased with degradation time due to an increased amount of L-lactide (L-LA) in the polymer matrix. The GC-MS analysis showed that up to 70% of the theoretical amount of 3-(2 hydroxycthyl)-propanoic acid and 10-20% of lactic acid was released after 23 weeks of degradation.
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| 46. |
- Száraz, Ildiko, et al.
(författare)
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A spectroscopic study of the solvation of 1-vinyl-2-pyrrolidone and poly(1-vinyl-2-pyrrolidone) in different solvents
- 2000
-
Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 41:13, s. 4831-4839
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Tidskriftsartikel (refereegranskat)abstract
- The solvation of 1-vinyl-2-pyrrolidone and poly(1-vinyl-2-pyrrolidone) in solvents of varying polarity, specifically water, ethylene glycol, chloroform and carbon tetrachloride, was investigated by means of Fourier transform infrared (FT-IR), FT-Raman, UV, 1H and 13C NMR spectroscopy. The IR and Raman measurements made it possible to establish the structures of the solvated molecules and the type of the hydrogen bonding that was obtained. From the UV results, the strength of the vinyl double bond was estimated in the different solvents. The 1H and 13C NMR spectra indicated that polar solvents interact with the solutes at the carbonyl group of the pyrrolidone ring, whereas nonpolar solvents interact mainly with the vinyl group in the 1-vinyl-2-pyrrolidone and with the polymer chain in poly(1-vinyl-2-pyrrolidone).
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| 47. |
- Wu, Q. J., et al.
(författare)
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FT-IR spectroscopic study of hydrogen bonding in PA6/clay nanocomposites
- 2002
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Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 43:8, s. 2445-2449
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Tidskriftsartikel (refereegranskat)abstract
- Fourier transform infrared spectroscopy was used to investigate PA6/clay nanocomposites (PA6CN) with various cooling histories from the melt, including rapid cooling (water-quenched), middle-rate cooling (air-cooling) and slow cooling (mold-cooling). In contrast to pure PA6 dominated by the alpha-phase, the addition of clay silicate layers favor the formation of the gamma-crystalline phase in PA6CN. We focus on the reason why silicate layers favor the formation of gamma-phase in PA6. Vaia et al. suggested that the addition of clay layers forces the amide groups of PA6 out of the plane formed by the chains. This results in conformational changes of the chains, which limits the formation of H-bonded sheets so that the gamma-phase is favored. If this assumption is correct, PA6CN is expected to show some differences as compared with PA6 with respect to hydrogen bonding. The silicate layers were indeed found to weaken the hydrogen bonding both in the alpha- and gamma-phases This was also confirmed by X-ray diffraction studies. The gamma-phase is most likely concentrated in regions close to the silicate layers, whereas the alpha-phase is favored in the bulk matrix.
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| 48. |
- Yousefi, H., et al.
(författare)
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Development and relaxation of orientation in sheared concentrated lyotropic solutions of hydroxypropylcellulose in m-cresol
- 2003
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Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 44:4, s. 1203-1210
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Tidskriftsartikel (refereegranskat)abstract
- Shear-induced orientation and the relaxation of orientation after the cessation of shear in 45 and 50 wt% solutions of cholesteric hydroxypropylcellulose (HPC) in m-cresol have been studied in situ by infrared spectroscopy and polarised microscopy. The shearing experiments were conducted at 30-80 degreesC at shear rates of 1-300 s(-1), which covered the director tumbling, wagging and a small part of the steady-state shear rate regimes. The steady-state order parameter was proportional to the shear rate and the proportionality constant increased with increasing HPC concentration and decreasing temperature. The concentrated solutions studied showed steady-state alignment even in the tumbling regime. Three different shear-rate regions with different behaviours of the solutions after the cessation of shear were found in these concentrated HPC solutions. At low shear rates (1-5 s(-1), referring to the 50% HPC solution) the polymer remained isotropic during shear but became gradually more oriented a few minutes after the cessation of shear, an observation that was substantiated by polarized microscopy. The order parameter reached a final plateau value and stayed constant at this level for long periods of time (similar to24 h). At intermediate shear rates (from 5 to 50 s(-1) for the 50% HPC solution), a detectable order parameter was recorded at steady shear and, after the cessation of shear, the structure returned to an almost isotropic state within a few minutes, after which the orientation gradually started to increase to approach a plateau value after about 150 min. At even higher shear rates (similar to100 s(-1) for to the 50% HPC solution), the initial steady shear order parameter relaxed to an almost isotropic state and remained constant at this level for time periods extending up to 24 h.
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| 49. |
- Zhou, Qi, et al.
(författare)
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Miscibility, free volume behavior and properties of blends from cellulose acetate and castor oil-based polyurethane
- 2003
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Ingår i: Polymer. - 0032-3861 .- 1873-2291. ; 44:5, s. 1733-1739
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Tidskriftsartikel (refereegranskat)abstract
- A series of blend films from cellulose acetate (CA) and castor oil-based polyurethane (PU) were prepared. Morphology, miscibility, free volume behavior and properties of such blend films were investigated by wide-angle X-ray diffraction (WXRD), infrared, scanning electron microscopy (SEM), differential scanning calorimetry (DSC), positron annihilation lifetime spectroscopy (PALS), thermogravimetric analysis and tensile test. The results indicated that lager free volume cavities did not form at the interface of two polymers although a certain degree of phase separation was found by the studies of SEM and DSC. Strong intermolecular hydrogen bonding interactions at the interface, which was proved by Fourier transform infrared spectroscopy, favors even better molecular packing, that is, PU dispersed in CA continuous phase to form fine microphase separation domain in the CA-rich blends. Due to such special interactions in the fine microphase separation domain structure, optimized properties of tensile strength, breaking elongation and cold-resistivity were obtained in the blend film with 75 wt% CA. The toughness of all the blend films was significantly higher than that of the film CA, owing to the plasticizing of PU elastomer in the blends.
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| 50. |
- Abrahamsson, Tobias, et al.
(författare)
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Investigating the role of polymer size on ionic conductivity in free-standing hyperbranched polyelectrolyte membranes
- 2021
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Ingår i: Polymer. - : Elsevier. - 0032-3861 .- 1873-2291. ; 223
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Tidskriftsartikel (refereegranskat)abstract
- Polymer-based ion exchange membranes (IEMs) are utilized for many applications such as in water desalination, energy storage, fuel cells and in electrophoretic drug delivery devices, exemplified by the organic electronic ion pump (OEIP). The bulk of current research is primarily focused on finding highly conductive and stable IEM materials. Even though great progress has been made, a lack of fundamental understanding of how specific polymer properties affect ionic transport capabilities still remains. This leads to uncertainty in how to proceed with synthetic approaches for designing better IEM materials. In this study, an investigation of the structure-property relationship between polymer size and ionic conductivity was performed by comparing a series of membranes, based on ionically charged hyperbranched polyglycerol of different polymer sizes. Observing an increase in ionic conductivity associated with increasing polymer size and greater electrolyte exclusion, indi-cating an ionic transportation phenomenon not exclusively based on membrane electrolyte uptake. These findings further our understanding of ion transport phenomena in semi-permeable membranes and indicate a strong starting point for future design and synthesis of IEM polymers to achieve broader capabilities for a variety of ion transport-based applications.
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