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  • 201. Pitois, C.
    et al.
    Hult, Anders
    KTH, Superseded Departments, Polymer Technology.
    Wiesmann, D.
    Absorption and scattering in low-loss polymer optical waveguides2001In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 18, no 7, p. 908-912Article in journal (Refereed)
    Abstract [en]

    The absolute absorption spectra of low-loss optical waveguides, together with their intrinsic and extrinsic scatterings, were measured in the near infrared. Photothermal deflection spectroscopy was used to measure the full absorption spectra of a series of fluorinated cross-linked polymers. Assignment of-CH3,-CH2-, and -OH overtones as well as of combinations of overtones were made by use of the theory of anharmonic vibrations based on a Morse potential for local modes. Details of the molecular potential are given. The total attenuation in slab waveguides made with these polymers was measured by a prism-coupling technique and compared with the absolute absorption. Losses that are due to the material itself and those that are due to the processing are quantified.

  • 202. Pitois, C.
    et al.
    Wiesmann, D.
    Lindgren, M.
    Hult, Anders
    KTH, Superseded Departments, Polymer Technology.
    Functionalized fluorinated hyperbranched polymers for optical waveguide applications2001In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 13, no 19, p. 1483-1487Article in journal (Refereed)
    Abstract [en]

    Fluorinated dendritic or hyperbranched polymers are demonstrated for the first time to be potentially useful for optical waveguide applications, for example in telecommunications. The required materials properties include the control of the refractive index over a wide range and UV-crosslinking for ease of processing and stable long-term mechanical properties. The authors report the synthesis of suitable functionalized fluorinated hyperbranched polymers and how the above requirements can be met by functionalization at the periphery of the polymers.

  • 203.
    Pitois, Claire
    KTH, Superseded Departments, Polymer Technology.
    Fluorinated polymer optical waveguides2001Doctoral thesis, comprehensive summary (Other scientific)
  • 204.
    Pitois, Claire
    et al.
    KTH, Superseded Departments, Fibre and Polymer Technology.
    Vestberg, Robert
    KTH, Superseded Departments, Fibre and Polymer Technology.
    Rodlert, Marlene
    Malmström, Eva
    KTH, Superseded Departments, Fibre and Polymer Technology.
    Hult, Anders
    KTH, Superseded Departments, Polymer Technology.
    Lindgren, M.
    Fluorinated dendritic polymers and dendrimers for waveguide applications2003In: Optical materials (Amsterdam), ISSN 0925-3467, E-ISSN 1873-1252, Vol. 21, no 1-3, p. 499-506Article in journal (Refereed)
    Abstract [en]

    I Fluorinated hyperbranched polymers and dendrimers with low optical losses and functionality to modify refractive index and add a cross-linking unit were developed. The results of refractive index. measurements indicate a tunability of the refractive index between approximately 1.5 and 1.6, and optical losses below 0.5 dB/cm at 1550 nm. Dendrimers with similar, surface group structure and possibility to surface functionalization were prepared using a lanthanide. cation as focal point. Results on luminescent properties in the NIR and IR regions were measured for lanthanide ions such as Nd3+ and Er3+, showing characteristic emission bands at 1.06, 1.3 and 1.5 mum. The associated absorption and excitation spectra were found similar to those of the corresponding ions in optical glasses.

  • 205. Qu, X.
    et al.
    Wirsen, A.
    Albertsson, Ann-Christine
    KTH, Superseded Departments, Polymer Technology.
    Effect of lactic/glycolic acid side chains on the thermal degradation kinetics of chitosan derivatives2000In: Polymer, ISSN 0032-3861, E-ISSN 1873-2291, Vol. 41, no 13, p. 4841-4847Article in journal (Refereed)
    Abstract [en]

    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.

  • 206. Qu, X.
    et al.
    Wirsen, A.
    Albertsson, Ann-Christine
    KTH, Superseded Departments, Polymer Technology.
    Novel pH-sensitive chitosan hydrogels: swelling behavior and states of water2000In: Polymer, ISSN 0032-3861, E-ISSN 1873-2291, Vol. 41, no 12, p. 4589-4598Article in journal (Refereed)
    Abstract [en]

    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.

  • 207. Qu, X.
    et al.
    Wirsen, A.
    Olander, B.
    Albertsson, Ann-Christine
    KTH, Superseded Departments, Polymer Technology.
    Surface modification of high density polyethylene tubes by coating chitosan, chitosan hydrogel and heparin2001In: Polymer Bulletin, ISSN 0170-0839, E-ISSN 1436-2449, Vol. 46, no 03-feb, p. 223-229Article in journal (Refereed)
    Abstract [en]

    Chitosan and chitosan hydrogel were immobilized on both the inside and outside surfaces of high density polyethylene (HDPE) tubes with 2.5x4 mm diameters. First, acrylic acid was grafted on the surfaces of HDPE by electron beam (2.5 Mrad) preirradiation method. Then chitosan/HCl and chitosan/lactic acid solutions were coated on the modified hydrophilic HDPE surfaces, the latter could form a pH-sensitive hydrogel layer on the surfaces. The tube surfaces were further modified with heparin by surface interpenetrating method to improve blood compatibility. ATR-FTIR and ESCA methods were used to characterize the coated surfaces. The morphology changes were monitored by Scanning Electron Microscope (SEM).

  • 208.
    Qu, Xin
    KTH, Superseded Departments, Polymer Technology.
    Novel pH-sensitive hydrogels based on lactic acid, glycolic acid and chitosan1999Doctoral thesis, comprehensive summary (Other scientific)
  • 209. Ranucci, E.
    et al.
    Liu, Y.
    Lindblad, M. S.
    Albertsson, Ann-Christine
    KTH, Superseded Departments, Polymer Technology.
    New biodegradable polymers from renewable sources. High molecular weight poly(ester carbonate)s from succinic acid and 1,3-propanediol2000In: Macromolecular rapid communications, ISSN 1022-1336, E-ISSN 1521-3927, Vol. 21, no 10, p. 680-684Article in journal (Refereed)
    Abstract [en]

    High molecular weight poly(ester carbonate)s have been prepared by a two-step chain-extension reaction performed on oligomeric alpha,omega-dihydroxy-terminated poly(1,3-propylene succinate) in turn obtained by thermal polycondensation of excess 1,3-propanediol with succinic acid. The new polymers have a biodegradable backbone and derive from renewable sources. Therefore, they have a potential as environment-friendly materials.

  • 210. Ranucci, E.
    et al.
    Sandgren, A.
    Andronova, N.
    Albertsson, Ann-Christine
    KTH, Superseded Departments, Polymer Technology.
    Improved polyimide/metal adhesion by chemical modification approaches2001In: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 82, no 8, p. 1971-1985Article in journal (Refereed)
    Abstract [en]

    To increase their adhesion to silver, polyimide (PI) surfaces were modified by sulfonation reactions by means of different experimental procedures. The results of these modification reactions were analyzed in terms of the variation of the surface chemical composition examined by X-ray photoelectron spectroscopy. Longtime reactions were also followed by monitoring the increase in weight of the PI films. Changes in the total surface free energy were evaluated by contact angle measurements with the sessil drop method. The influence of the modification reactions on silver/PI adhesion was estimated by means of a 180 degrees peeling test according to ASTM standards. Finally, the effect of chemical modification on film roughness was investigated by means of atomic force microscopy. The results obtained showed that a net improvement, that is, over the maximum rate according to the reference ASTM test, was attained via both the gaseous SO3 and concentrated H2SO4 procedures, with the latter procedure more effective in the presence of silver sulfate as a catalyst. However, the former was judged more convenient because of the low amount of reagents used and the simplicity of cleaning operations. Interestingly, optimum adhesion levels were attained after only very low contact times with all sulfonating agents, that is, after about 30 s. These results were compared with the effects on PI/silver adhesion of traditional etching procedures with KOH aqueous solutions at different temperatures. In this case, good adhesion was observed only after longer reaction times, that is, on the order of 1-2 min in the case of IM KOH and 1 h in the case of 0.1M KOH.

  • 211. Ranucci, E.
    et al.
    Tarabic, M.
    Gilberti, M.
    Albertsson, Ann-Christine
    KTH, Superseded Departments, Polymer Technology.
    New ester and lactone end-functionalized N-vinyl-2-pyrrolidinone oligomers2000In: Macromolecular Chemistry and Physics, ISSN 1022-1352, E-ISSN 1521-3935, Vol. 201, no 12, p. 1219-1225Article in journal (Refereed)
    Abstract [en]

    New oligomers of N-vinyl-2-pyrrolidinone functionalized at one end with either ester or lactone functions were obtained by radical polymerization in the presence of different ester (methyl isobutyrate and methyl phenylacetate) and lactone (epsilon-caprolactone, delta-valerolactone and gamma-btyrolactone) compounds as chain transfer agents. The oligomeric samples obtained were characterized in terms of molecular weight and molecular weight distribution by means of analytical size exclusion chromatography (SEC), using purposely synthesized poly(N-vinyl-2-pyrrolidinone) standards. The chain transfer constant C-tau of either methyl isobutyrate, delta-valerolactone, or gamma-butyrolactone towards N-vinyl-2-pyrrolidinone were determined with the help of the known cumulative number-average degree of polymerization (X) over bar(n) and monomer conversion Y-t of the samples during the reaction.

  • 212.
    Renstad, Rasmus
    KTH, Superseded Departments, Polymer Technology.
    Influence of processing and processing additives on the degradation of aliphatic polyesters1998Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Poly(3-hydroxybutyrate-co-3-hydroxyvalerate), P(3HB-co-3HV),poly(ε-caprolactone), PCL, and poly(lactic acid), PLA,have been subjected to film-blowing, melt-extrusion andmelt-pressing. The influence of processing conditions andprocessing additives (i.e. plasticizer, antiblocking and slipagents) on properties and degradation have been studied. Thepolyesters were exposed to pure fungal cultures(Aspergillus fumigatus,Phanerochaete chrysosporiumandPenicillium simplicissi-mum), composting and chemicalhydrolysis.

    The molecular weight of P(3HB-co-3HV) decreased withincreasing processing temperature and decreasing screw speedduring melt-extrusion. The mechanical properties were dependenton the molecular weight. The tensile strength decreased rapidlyat weight average molecular weights below 150 000 g/mol. Thedegree of crystallinity was largely unaffected by the extrusionconditions. An increase in the processing temperature increasedthe intensity of the (020) reflection and decreased theintensity of the (110) reflection. The changes in thediffraction patterns indicate changes in the positions of theoxygen atoms due to differences in the torsion angles in themain chain bonds. The rate of bioerosion in pure fungalcultures for P(3HB-co-3HV) was highest for the samplesexhibiting high peak ratio of the (020) and (110) reflectionsindicating that the changes in the positioning of the oxygenatoms affect the recognition capability of the extra-cellularenzymes. The erosion rate was not controlled by molecularweight or lamellar distribution, however, it decreased withincreasing degree of crystallinity.

    Film-blowing caused minor reductions in the molecular weightof PCL. Film blown from reprocessed PCL, and from reprocessedPCL containing additives exhibited lower degradation rates incompost than films from virgin PCL. The difference could beattributed to the reprocessing rather than the additives.Melt-pressed PCL film with SiO2(5.0 w%) exhibited higher erosion rates than purePCL during composting and exposure toA. fumigatus. Melt-pressed film with erucamide (1.0 w%)exhibited higher hydrophobicity but no reduction of thebiodegradation rate was observed. The rate of biodegradationfor PCL increasedwith decreasing film thickness. Thebiodegradation of P(3HB-co-3HV) and PCL was characterized bysignificant weight loss with minor reductions of the molecularweight.

    Film-blowing caused a 50 % decrease in the weight averagemolecular weight of PLA. CaCO3(2 w%) added to PLA reduced the chain scissionduring melt-processing. However, the rate of (bio)degradationwas also reduced. SiO2(5 w%) added to PLA did not affect the thermaldegradation or the rate of biodegradation. The (bio)degradationof PLA was characterized by significant reductions in molecularweight due to chemical hydrolysis. The onset of biodegradationoccurred when the molecular weight was sufficiently reduced.Extracellular enzymes fromA. fumigatuswere more effective in degrading PLA thanthose fromP. simplicissimum.

  • 213. Rigdahl, M
    et al.
    Riha, P
    Rychwalski, R W
    Kubat, M. J.
    KTH, Superseded Departments, Polymer Technology.
    Kubat, J.
    The clustering mechanism underlying a kinetic model related to Bose-Einstein statistics2004In: Mechanics of time-dependant materials, ISSN 1385-2000, E-ISSN 1573-2738, Vol. 8, no 2, p. 95-103Article in journal (Refereed)
    Abstract [en]

    The present paper discusses the clustering of elementary events in a kinetic relaxation model based on a time-domain analog of Bose-Einstein statistics. The clustering results in a spectrum of relaxation times which are integer-valued fractions of the relaxation time of single events, thus providing a stretching of the overall process towards shorter times. The predictions of the model are combined with an expression describing the 'universal' behaviour of solids of various structure and composition in a stress relaxation experiment. This yields the remarkable result that the average cluster size relating to the entire process is six. Correspondingly, the average relaxation time is found to be 1/6 of the relaxation time of the single events.

  • 214.
    Roseen, Patrik A.
    KTH, Superseded Departments, Polymer Technology.
    Electrical properties of thermally aged polyethylenes and of polyethylenes containing voltage stabilisers1998Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The use of polyethylene (PE) in electrical applications athigh voltages requires a certain resistance of the material topartial discharges (PDs). The space charge behaviour of PE isof great importance when PE is used as insulator inhigh-voltage DC cables. The long service lifetime ofhigh-voltage equipment makes the long-term properties of PEvery important. In this thesis the PD resistance was assessedby PD lifetime measurements and the space charge behaviour bypulsed electro-acoustic (PEA) measurements. The long-termproperties were assessed by accelerated ageing at elevatedtemperatures.

    The PD lifetime of a wide range of thermoplastic andcrosslinked PEs - including compounds containing aromaticvoltage stabilisers (fluoranthene, naphthalene, pyrene,o-terphenyl, vinylnaphthalene and anthracene) - were studied.The PD lifetime was essentially independent of molar mass,degree of crosslinking, crystallinity and crystal thickness. Avery brittle, monodisperse, low molar mass sample deviated byshowing a reduced PD lifetime. The added voltage stabilisershad no effect on the PD lifetime.

    Films of a range of PEs with different degrees ofcrystallinity were aged in air at 100ºC, 115ºC and130ºC for periods up to 28 500 hours, and subsequentlytheir PD lifetime and space charge behaviour were measured. Thefilms were characterised by stress-strain measurements,differential scanning calorimetry, infrared spectroscopy andsize exclusion chromatography.

    Mere oxidation was not sufficient to cause a decrease in PDlifetime, unless the carbonyl content exceeded a certainthreshold value above which the PD lifetime decreased rapidlywith increasing concentration of carbonyl groups. It issuggested that the carbonylic groups enhance radical formationand thereby accelerate surface erosion, causing early PDbreakdown. The PD lifetime and the space charge behaviour werenot influenced by the effective antioxidant concentration.Oxidation facilitated charge injection and hetero-chargeformation, and the presence of polar groups in the polymermolecules decreased the mobility of the charges. The resultsalso indicate that the transport of the charges occurredprimarily in the non-crystalline components and that thepresence of large crystallites reduced the "migration" rate ofthe charges. Charge packages were formed at the cathode for oneoxidised high-voltage PE grade. It is suggested that thesepackages are due to charge separation and faster migration ofthe negative charges than of the positive charges. It is alsosuggested that volatile species cause the charge packagegeneration.

    Keywords:polyethylene, voltage stabilisers, thermaloxidation, carbonyl group content, carbonyl containing modelmaterials, partial discharges, corona, space charges, pulsedelectro-acoustic method (PEA).

  • 215. Rutkowska, A.
    et al.
    Krasowska, K.
    Heimowska, A.
    Steinka, I.
    Janik, H.
    Haponiuk, J.
    Karlsson, Sigbritt
    KTH, Superseded Departments, Polymer Technology.
    Biodegradation of modified poly(epsilon-caprolactone) in different environments2002In: Polish Journal of Environmental Studies, ISSN 1230-1485, E-ISSN 2083-5906, Vol. 11, no 4, p. 413-420Article in journal (Refereed)
    Abstract [en]

    The comparison of degradation of modified poly(epsilon-caprolactone) film in different environments is presented. Poly(epsilon-caprolactone) was incubated in a natural environment - sea water (the Baltic Sea), in buffered salt solution, in liquid medium containing sea water with NaN3 and in compost with plant treatment activated sludge (under natural and laboratory conditions). The characteristic parameters of sea water and compost with active sludge are described. Their influence on degradation of modified poly(epsilon-caprolactone) is discussed. Weight changes, viscosity, tensile strength, DSC parameters of melting and crystallization and changes in morphology of polymer surface were tested during the period of biodegradation. In liquid medium containing sea water with sodium azide and in buffered salt solution the slow hydrolysis process of poly(epsilon-caprolactone) was observed. In natural environments the poly(epsilon-caprolactone) film was completely assimilated after seven weeks of incubation. This means that poly(epsilon-caprolactone) modified by slip and anti-block one additives was very sensitive to an enzymatic attack by microorganisms present in the Baltic Sea water and in the compost with activated sludge under natural conditions.

  • 216. Ryner, M.
    et al.
    Albertsson, Ann-Christine
    KTH, Superseded Departments, Polymer Technology.
    Resorbable and highly elastic block copolymers from 1,5-dioxepan-2-one and L-lactide with controlled tensile properties and hydrophilicity2002In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 3, no 3, p. 601-608Article in journal (Refereed)
    Abstract [en]

    New resorbable and elastomeric ABA tri- and multiblock copolymers have been successfully synthesized by combining ring-opening polymerization with ring-opening polycondensation. Five different Poly(L-lactide-b-1,5-dioxepan-2-one-b-L-lactide) triblock copolymers and one new Poly(L-lactide-b-1,5-dioxepan-2-one) multiblock copolymer have been synthesized. The triblock copolymers were obtained by ring-opening polymerization of 1,5-dioxepan-2-one (DXO) and L-lactide (LLA) with a cyclic tin initiator. The new multiblock copolymer was prepared by ring-opening polycondensation of a low molecular weight triblock copolymer with succinyl chloride. The molecular weight and the composition of the final copolymers were easily controlled by adjusting the monomer feed ratio, and all of the polymers obtained had a narrow molecular weight distribution. It was possible to tailor the hydrophilicity of the materials by changing the DXO content. Copolymers with a high DXO content had a more hydrophilic surface than those with a low DXO content, The receding contact angle varied from 27 to 44degrees. The tensile proper-ties of the copolymers were controlled by altering the PDXO block length. The tensile, testing showed that all the polymers were very elastic and had very high elongations-at-break (epsilon(b)). The copolymers retained very good mechanical properties (epsilon(b) approximate to 600-800% and sigma(b) approximate to 8-20 MPa) throughout the in vitro degradation study (59 days).

  • 217. Ryner, M.
    et al.
    Albertsson, Ann-Christine
    KTH, Superseded Departments, Polymer Technology.
    Tailored mechanical properties and degradability of polyesters by controlled molecular architecture2001In: Macromolecular Symposia, ISSN 1022-1360, E-ISSN 1521-3900, Vol. 175, p. 11-18Article in journal (Refereed)
    Abstract [en]

    Advanced molecular architectures have been used as a toot for tailoring the mechanical properties and the degradation process of polymers for specific applications. Crosslinked poly(1,5-dioxepan-2-one), random poly(1,5-dioxepan-2-one-co-L-lactide), triblock poly(L-lactide-b-1,5-dioxepan-2-one-b-L-lactide) and triblock poly(epsilon -caprolactone-b-1,5-dioxepan-2-one-b-epsilon -caprolactone) have been synthesized and their thermal and mechanical properties as well as degradation times and degradation products have been characterized and compared. The stress at break of the synthesized polymers ranged from 4 MPa to 55 MPa and the elongation at break from 25% to 1200%. The degradation time varied from 70 days up to 360 days. These polymers are suitable as films or microspheres for controlled drug delivery or as temporary tissue replacements e.g. for tendons or nerve guides.

  • 218. Ryner, M.
    et al.
    Stridsberg, K.
    Albertsson, Ann-Christine
    KTH, Superseded Departments, Polymer Technology.
    von Schenck, H.
    Svensson, M.
    Mechanism of ring-opening polymerization of 1,5-dioxepan-2-one and L-lactide with stannous 2-ethylhexanoate. A theoretical study2001In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 34, no 12, p. 3877-3881Article in journal (Refereed)
    Abstract [en]

    A theoretical study of the ring-opening polymerization (ROP) mechanism of 1,5-dioxepana-2-one (DXO) and (L)-lactide (LLA) with stannous(IE) a-ethylhexanoate (Sn(Oct)(2)) is presented. The B3LYP density functional method has been used for the quantum chemical calculations. Our results support a coordination-insertion mechanism initiated by a tin-alkoxide species formed prior to the ROP. The rate-determining step in the ROP was the nucleophilic attack of the alkoxide on the carbonyl carbon of the monomer. The activation energy for the ROP of DXO with Sn(Oct ')(2) has been determined to be 19.8 kcal/mol and for L-lactide 20.6 kcal/mol. At normal reaction temperatures, a ligand may dissociate as Oct 'H during propagation. An excess of carboxylic acid hinders the coordination of monomer to the initiating/propagating complex.

  • 219. Ryner, M.
    et al.
    Valdre, A.
    Albertsson, Ann-Christine
    KTH, Superseded Departments, Polymer Technology.
    Star-shaped and photocrosslinked poly(1,5-dioxepan-2-one): Synthesis and characterization2002In: Journal of Polymer Science Part A: Polymer Chemistry, ISSN 0887-624X, E-ISSN 1099-0518, Vol. 40, no 12, p. 2049-2054Article in journal (Refereed)
    Abstract [en]

    New star-shaped and photocrosslinked poly(1,5-dioxepan-2-one) (PDXO) has been synthesized through ring-opening polymerization initiated by SnOct(2)/pentaerythritol. The star-shaped PDXO was end-functionalized by acrolyol chloride to form acrylate end groups. The end-functionalized PDXO was photocrosslinked initiated by 2,2-dimethoxy-2-phenylacetophenone. The gel content ranged from 80 to 99%, indicating a high degree of crosslinking. The thermal properties of the star-shaped PDXO and the photocrosslinked PDXO were analyzed by differential scanning calorimetry. The glass-transition temperature was determined to approximately -32 degreesC for the crosslinked PDXO. The viscosity numbers were determined for star-shaped PDXO, with reference to linear homologues. The star-shaped PDXO had lower viscosity numbers than the linear counterparts, The crosslinked PDXO showed a rather hydrophilic surface as compared with other resorbable polyesters. The advancing contact angle was 64 +/- 2, and the receding angle was 57 +/- 4.

  • 220.
    Ryner, Maria
    KTH, Superseded Departments, Polymer Technology.
    Controlled Ring-Opening Polymerization: Mechanism and Synthesis of Macromolecular Architectures with Tailored Properties2002Doctoral thesis, comprehensive summary (Other scientific)
  • 221. Ryner, Maria
    et al.
    Finne, Anna
    KTH, Superseded Departments, Polymer Technology.
    Albertsson, Ann-Christine
    KTH, Superseded Departments, Polymer Technology.
    Kricheldorf, Hans R.
    L-lactide macromonomer synthesis initiated by new cyclic tin alkoxides functionalized for brushlike structures2001In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 34, no 21, p. 7281-7287Article in journal (Refereed)
    Abstract [en]

    L-Lactide macromonomers with an incorporated double bond were successfully synthesized by controlled ring-opening polymerization initiated by two new cyclic tin alkoxides (1,1-di-n-butyl-stanna-2,7-dioxacyclo-4-heptene and 9,9,20,20-tetrabutyl-8,10,19,21-tetraoxa-9,20-distanna-dispiro[5.5.5.5]d ocosa-2,14-diene). Initiators and crude reaction mixtures were characterized by NMR. H-1 NMR analysis showed that the initiators were completely reacted in the polymerization and that both tin-oxygen bonds were reactive and participated in propagation. The polymerizations were performed in chloroform at 60 degreesC, and the molecular weight was effectively controlled by adjusting the monomer-to-initiator ratio. The molecular weight distribution was narrow (<1.1) for both high and low molecular weights (3000-72 000 g/mol). A plot of M-n vs conversion was linear up to a conversion of 98%, showing a system propagating in a controlled manner. The kinetic investigation showed that all of the polymerizations were first order in monomer and that no termination reactions occurred during polymerization.

  • 222. Samuelsson, J.
    et al.
    Johansson, Mats K. G.
    KTH, Superseded Departments, Polymer Technology.
    A study of fatty acid methyl esters with epoxy or alkyne functionalities2001In: Journal of the American Oil Chemists Society, ISSN 0003-021X, E-ISSN 1558-9331, Vol. 78, no 12, p. 1191-1196Article in journal (Refereed)
    Abstract [en]

    Described are the physical and chemical properties of the methyl esters of two uncommon fatty acids: vernolic acid, containing an epoxy group, and crepenynic acid, containing a triple bond. The incorporation of an epoxy or alkyne group into the fatty acid structure is shown to greatly affect the properties compared to conventional unsaturated fatty acids, The methyl esters have been characterized and compared with ordinary fatty acid methyl esters (i.e., methyl oleate and linoleate) with respect to spectroscopic characterization [H-1 nuclear magnetic resonance (NMR)], C-13 NMR, and Fourier transform infrared), rheological properties, and oxidative reactivity (using chemiluminescence), Both methyl vernoleate and methyl crepenynate could successfully be produced by transesterification under basic conditions without reaction of the epoxy or alkyne groups. Rheological measurements showed that the methyl esters had a significantly lower viscosity compared to their triglyceride analogs. Smaller differences were seen when comparing the different methyl esters where methyl vernoleate had the highest viscosity due to the presence of the more polar oxirane group. Very large differences were found with respect to the oxidation rate of the different methyl esters. Methyl crepenynate was shown to oxidize extremely rapidly, whereas methyl vernoleate was very stable toward oxidation.

  • 223. Samuelsson, J.
    et al.
    Johansson, Mats K. G.
    KTH, Superseded Departments, Polymer Technology.
    Oxidation of FA with alkene or alkyne functionalities studied with chemiluminescence and real-time IR spectroscopy2003In: Journal of the American Oil Chemists Society, ISSN 0003-021X, E-ISSN 1558-9331, Vol. 80, no 5, p. 491-496Article in journal (Refereed)
    Abstract [en]

    The oxidation of well-defined FA derivatives has been studied with real-time IR (RTIR) and chemiluminescence (CL) techniques. Both methyl esters and model oils based on different FA have been studied to reveal the effect of functionality. The FA used were linoleic and crepenynic acid, the latter with an alkyne functionality. The purpose was to reveal how structural differences affect the oxidation and how this is monitored with CL and RTIR. Both model oils had longer oxidation induction times than the corresponding methyl esters, as seen by both IR and CL. Generally, the induction times measured with IR were shorter than those determined by CL, but the rate of oxidation did not seem to differ much between the model oils and the corresponding methyl esters. The results also imply that the higher functionality of the model oils gives a greater possibility of intramolecular addition reactions instead of chain scission during oxidation, making the model oi Is emit fewer low-M.W. volatiles than the methyl esters. There is also a difference between methyl crepenynate and methyl linoleate, in that the alkyne functionality seems to enhance the possibility of chain scission instead of addition reactions. The results presented imply that the CL signal can be used to monitor the oxidation and the formation of volatile compounds from a FA structure. By combining the CL measurements with RTIR data, information about the oxidation reactions can be obtained, giving a greater understanding of what reactions are occurring during oxidation and how they are related to each other.

  • 224.
    Samuelsson, Johan
    KTH, Superseded Departments, Polymer Technology.
    A study of new fatty acid derivatives as monomers for coating applications2002Licentiate thesis, comprehensive summary (Other scientific)
  • 225. Sandelin, M. J.
    et al.
    Gedde, Ulf W.
    KTH, Superseded Departments, Polymer Technology.
    Long-term performance of cables based on chlorosulphonated polyethylene2004In: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321, Vol. 86, no 2, p. 331-338Article in journal (Refereed)
    Abstract [en]

    Cables based on chlorosulphonated polyethylene were aged at different temperatures between 120 and 200 degreesC and their conditions were assessed by mechanical methods: micro-indenter and tensile testing. Some of the cables were not aged prior to the oven ageing whereas other cables had been exposed to almost 25 years of service at controlled temperatures (30-54 degreesC) and atmospheres (nitrogen and air). An indenter modulus twice that of the initial value was used as a lifetime criterion; the criterion is based on earlier reported data on similar cables from LOCA tests simulating nuclear power plant failure. The remaining lifetime of the cables exposed to almost 25 years of service was determined by a second-stage ageing at 155 and 170 degreesC and a comparison with lifetime data obtained for unexposed cable samples. The lifetime data, covering a very broad range of temperatures (40-200 degreesC), obeyed the Arrhenius law with the following values for the activation energy depending on the surrounding atmosphere: I I I +/- 5 (nitrogen) and 96 +/- 5 U mol(-1) (air). Air was found to be a more degrading environment than nitrogen at all the temperatures studied.

  • 226.
    Sandgren, Åsa
    KTH, Superseded Departments, Polymer Technology.
    Physical and chemical surface modifications of a polyimide to enhance its adhesion to silver2001Licentiate thesis, comprehensive summary (Other scientific)
  • 227.
    Skytt, Marie-Louise
    KTH, Superseded Departments, Polymer Technology.
    Rheo-infrared dichroism studies of sheared molten flexible-chain and liquid-crystalline polymers1997Doctoral thesis, comprehensive summary (Other scientific)
  • 228. Stridsberg, K.
    et al.
    Albertsson, Ann-Christine
    KTH, Superseded Departments, Polymer Technology.
    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 degradation2000In: Polymer, ISSN 0032-3861, E-ISSN 1873-2291, Vol. 41, no 20, p. 7321-7330Article in journal (Refereed)
    Abstract [en]

    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.

  • 229. Stridsberg, K.
    et al.
    Albertsson, Ann-Christine
    KTH, Superseded Departments, Polymer Technology.
    Controlled ring-opening polymerization of L-lactide and 1,5-dioxepan-2-one forming a triblock copolymer2000In: Journal of Polymer Science Part A: Polymer Chemistry, ISSN 0887-624X, E-ISSN 1099-0518, Vol. 38, no 10, p. 1774-1784Article in journal (Refereed)
    Abstract [en]

    Novel elastomeric A-B-A triblock copolymers were successfully synthesized in a new two-step process: controlled ring-opening polymerization of the cyclic etherester 1.5-dioxepan-2-one as the amorphous middle block (B-block) followed by addition and polymerization of the two semicrystalline L-lactide blocks (A-block). A 1,1,6,6-tetra-n-butyl-1,6-distanna-2,5,7,10-tetraoxacyclodecane initiator system was utilized and the reaction was performed in chloroform at 60 degrees C. A good control of the synthesis was obtained, resulting in well defined triblock copolymers. The molecular weight and chemical composition were easily adjusted by the monomer-to-initiator ratio. The triblock copolymers formed exhibited semicrystallinity up to a content of 1,5-dioxepan-2-one as high as 89% as determined by differential scanning calorimetry. WAXS investigation of the triblock copolymers showed a crystal structure similar to that of the pure poly(L-lactide).

  • 230. Stridsberg, K.
    et al.
    Ryner, M.
    Albertsson, Ann-Christine
    KTH, Superseded Departments, Polymer Technology.
    Dihydroxy-terminated poly(L-lactide) obtained by controlled ring-opening polymerization: Investigation of the polymerization mechanism2000In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 33, no 8, p. 2862-2869Article in journal (Refereed)
    Abstract [en]

    Hydroxy telechelic poly(L-lactide)s of different molecular weight have been synthesized by controlled ring-opening polymerization using cyclic tin alkoxides. NMR analysis showed that the propagation proceeded through an insertion mechanism. No free hydroxyl or carboxyl end groups were detected in the polymerization mixture. Complete reaction of the initiator was observed over the entire range of compositions studied. Both tin-oxygen bonds were reactive and participated in the propagation reaction. Peak assignments were obtained by H-1, C-13, distortionless enhancement polarization transfer (DEPT), and heteronuclear multiple quantum coherence-gradient selected (hmqc-gs) nuclear magnetic resonance spectroscopy. The kinetics of the solution polymerization of L-lactide has been investigated and showed a first order in monomer. The external order in initiator has been determined to be 3/4 for initiator concentrations above 5 mmol/L and to 2 below 2 mmol/L. The molecular weight could easily be adjusted by the monomer-to-initiator ratio, and the molecular weight distribution remained narrow even at high molecular weight(MWD < 1.15). The polymerization products were characterized by size exclusion chomatography (SEC) as well as H-1 and C-13 NMR.

  • 231.
    Stridsberg, Kajsa
    KTH, Superseded Departments, Polymer Technology.
    Controlled ring-opening polymerization: Polymers with designed macromolecular architechture2000Doctoral thesis, comprehensive summary (Other scientific)
    Download full text (pdf)
    FULLTEXT01
  • 232.
    Sturesson, Cecilia
    KTH, Superseded Departments, Polymer Technology.
    Biodegradable microspheres for drug delivery1998Licentiate thesis, comprehensive summary (Other scientific)
  • 233.
    Söderqvist-Lindblad, Margaretha
    et al.
    KTH, Superseded Departments, Polymer Technology.
    Albertsson, Ann-Christine
    KTH, Superseded Departments, Polymer Technology.
    Chemical Modifications of Hemicelluloses and Gums2004In: Polysaccharides: Structural Diversity and Functional Versatility / [ed] Severian Dumitriu, CRC Press, 2004, 2, p. 491-508Chapter in book (Other academic)
  • 234. Tall, S.
    et al.
    Albertsson, Ann-Christine
    KTH, Superseded Departments, Polymer Technology.
    Karlsson, Sigbritt
    KTH, Superseded Departments, Polymer Technology.
    Enhanced rigidity of recycled polypropylene from packaging waste by compounding with talc and high-crystallinity polypropylene2001In: Polymers for Advanced Technologies, ISSN 1042-7147, E-ISSN 1099-1581, Vol. 12, no 5, p. 279-284Article in journal (Refereed)
    Abstract [en]

    Polypropylene (PP) constituted 30% of the collected material in a Swedish collection system for rigid plastic packaging waste. The PP fraction was however a complex mixture of grades with widely different properties. In order to enhance the rigidity of the recycled PP, modified grades were prepared by compounding with talc and/or a virgin high-crystallinity PP grade, Adding 20-40% of high-crystallinity PP enhanced the stiffness and yield strength without impairing the impact resistance. A composite material consisting of 20% of this grade, 20% talc and 60% recycled PP gave mechanical properties similar to those of a commercial talc filled PP compound used for demanding engineering applications. The present study demonstrates that recycled PP derived from post-consumer packaging waste can also be made useful for demanding engineering applications.

  • 235.
    Tall, Stefan
    KTH, Superseded Departments, Polymer Technology.
    Recycling of mixed plastic waste2000Doctoral thesis, comprehensive summary (Other scientific)
    Download full text (pdf)
    FULLTEXT01
  • 236. Ullsten, N. H.
    et al.
    Hedenqvist, Mikael S.
    KTH, Superseded Departments, Polymer Technology.
    A new test method based on head space analysis to determine permeability to oxygen and carbon dioxide of flexible packaging2003In: Polymer testing, ISSN 0142-9418, E-ISSN 1873-2348, Vol. 22, no 3, p. 291-295Article in journal (Refereed)
    Abstract [en]

    A new technique for determining oxygen and carbon dioxide permeabilities of flexible packaging was developed and tested on very-low density, low density and high density polyethylene pouches. The pouch head-space and pouch volume of carbon dioxide filled pouches were measured as a function of time until an equilibrium pouch gas composition was established. Permeabilities were obtained from the rates of carbon dioxide loss and oxygen uptake. HSP-method permeability values were in good agreement with those obtained from traditional flat-film permeability techniques. The HSP-method was found to be a valuable tool for determining and quantifying changes in carbon dioxide and oxygen pouch barrier properties due, for example, to exposure to olive oil or due to the existence of poor welds.

  • 237. Valles-Lluch, A.
    et al.
    Camacho, W.
    Ribes-Greus, A.
    Karlsson, Sigbritt
    KTH, Superseded Departments, Polymer Technology.
    Influence of water on the viscoelastic behavior of recycled nylon 6,62002In: Journal of Applied Polymer Science, ISSN 0021-8995, E-ISSN 1097-4628, Vol. 85, no 10, p. 2211-2218Article in journal (Refereed)
    Abstract [en]

    Nylons are highly sensitive to moisture, as water molecules are able to form hydrogen-bonded complexes with nitrogen and oxygen from the amide functional groups. In recycled nylon 6,6, a higher absorbed moisture content can be detected in comparison to virgin material. Moisture uptake is manifested in chemical and physical properties, and has important technological consequences, so the relationship between them must be assessed. Differential scanning calorimetry (DSC) has been used to measure the water content of different samples and physical changes have been analyzed by means of dynamic mechanical thermal analysis (DMTA). The relaxation zones of the dynamic-mechanical relaxation spectra of the samples have been characterized according to the Fuoss-Kirkwood equation and with help of the deconvolution method.

  • 238. Vestberg, R
    et al.
    Westlund, R
    Carlsson, M
    Eliasson, B
    Glimsdal, E
    Ortengren, J
    Lindgren, M
    Malmström, Eva
    KTH, Superseded Departments (pre-2005), Polymer Technology.
    Photophysical properties of dendronized platinum(II) acetylides for optical power limiting.2005In: Abstracts of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 229, p. U1157-U1157Article in journal (Other academic)
  • 239. Vestherg, R
    et al.
    Nystrom, A M
    Carlsson, M
    Eliasson, B
    Nilsson, C
    Eriksson, A
    Lopes, C
    Lindgren, M
    Malmström, Eva
    KTH, Superseded Departments (pre-2005), Polymer Technology.
    Dendron decorated chromophores for optical power limiting applications.2005In: Abstracts of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 229, p. U1162-U1162Article in journal (Other academic)
  • 240. von Schenck, H.
    et al.
    Ryner, M.
    Albertsson, Ann-Christine
    KTH, Superseded Departments, Polymer Technology.
    Svensson, M.
    Ring-opening polymerization of lactones and lactides with Sn(IV) and Al(III) initiators2002In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 35, no 5, p. 1556-1562Article in journal (Refereed)
    Abstract [en]

    A theoretical study is presented of the ring-opening polymerization (ROP) mechanism of 1,5-dioxepan-2-one (DXO) and glycolide with Sn(II) and Al(III) alkoxide initiators (SnMe3MeO, SnMe2-(MeO)(2), and AlMe2MeO). The B3LYP density functional method has been used to perform the quantum chemical calculations. A coordination-insertion mechanism is presented with two principal reaction steps. First, the alkoxide of the initiator performs a nucleophilic attack on the carbonyl carbon, and the carbonyl bond is broken. An intermediate is formed at this point, where the former carbonyl oxygen of the monomer is coordinated to tin via an alkoxide bond, while the carbonyl carbon assumes a sp(3) bonding geometry. The second step involves the acyl-oxygen cleavage of the monomer. For all three initiators it was found that the transition state involving the breaking of the carbonyl double bond (TS1) represented the highest point on the potential energy surface for DXO. For glycolide, however, the transition state of the acyl-oxygen cleavage (TS2) was the least stable structure. The reaction barriers were calculated to 17.1 kcal/mol for DXO/SnMe3MeO, 18.7 kcal/mol for glycolide/SnMe3MeO, 14.3 kcal/mol for DXO/SnMe2(MeO)(2), 14.5 kcal/mol for glycolide/SnMe2(MeO)(2), 13.6 kcal/mol for DXO/AlMe2MeO, and 9.3 kcal/mol for glycolide/AlMe2MeO. Both electronic and steric properties of the monomer affect the reaction barriers. It was found that the more electrophilic initiators polymerized cyclic esters faster.

  • 241.
    Wallström, Stina
    et al.
    KTH, Superseded Departments, Polymer Technology.
    Dowling, K.
    Karlsson, Sigbritt
    KTH, Superseded Departments, Polymer Technology.
    Development and comparison of test methods for evaluating formation of biofilms on silicones2002In: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321, Vol. 78, no 2, p. 257-262Article in journal (Refereed)
    Abstract [en]

    Silicone rubber formulations used for outdoor high voltage insulation are sometimes reported to be colonized by microorganisms. Different formulations show different sensitivity towards biological growth. In this study five rubbers were tested. Two standard practices were used, ASTM G21-90 and IEC 68-2-10. In addition a new method was developed to measure the rate of colonisation of a sample by biological growth. Results showed that the tested rubbers supported fungal growth when an external carbon source was available. Thus none of the silicones can be called bio-resistant. However the materials are not biodegradable either. This was clearly shown when mould spores were added to the samples in clean water, when none of the rubbers was contaminated. Some of the materials did, however, support growth when only nutrient salts, no carbon source, was added. The most bioresistant formulations contained the flame retardant zinc borate, indicating that this additive suppresses fungal growth. Further investigation with the new method supported that theory.

  • 242. Westlund, R
    et al.
    Carlmark, Anna
    KTH, Superseded Departments (pre-2005), Polymer Technology.
    Saez, I M
    Malmström, Eva
    KTH, Superseded Departments (pre-2005), Polymer Technology.
    Grafting liquid crystalline polymers from cellulose using ATRP.2005In: Abstracts of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 229, p. U981-U981Article in journal (Other academic)
  • 243. Westphal, C.
    et al.
    Perrot, C.
    Karlsson, Sigbritt
    KTH, Superseded Departments, Polymer Technology.
    Py-GC/MS as a means to predict degree of degradation by giving microstructural changes modelled on LDPE and PLA2001In: Polymer degradation and stability, ISSN 0141-3910, E-ISSN 1873-2321, Vol. 73, no 2, p. 281-287Article in journal (Refereed)
    Abstract [en]

    The degree of changes in the patterns and ratio of peaks (oligomers) in pyrograms from pyrolysed polymers exposed to hydrolysis (chemical and/or biological) and oxidation are related the extent of degradation and could be used to predict life-time. PLA and LDPE with enhanced degradability (LDPE with LLDPE, corn starch and pro-oxidant [SBS + manganese stearate (MB)] were used as models for hydrolysable and oxidisable polymers and pyrolysis gas chromatography mass spectrometry (Py-GC/MS) analysed for its versatility show differences in microstructure of polymers. In parallel size exclusion chromatography (SEC), gas chromatography mass spectrometry (GC-MS) and Fourier transform infrared spectroscopy (FTIR) gave other signs of degradation. Pyrolysed LDPE samples gave fragments constituting a triplet from C-6, to C-30, With a peak maxima at C-10, C-14 and C-18 expect for LDPE with pro-oxidant and starch exposed to thermo-oxidation. This sample instead had a high amount of C-9 fragment which is related to hydrogen abstraction occuring along the chain. FTIR showed that this samples had formed higher amounts of carbonyl compounds at the surface. Thermogravimetry analysis (TGA) gave changes in the constituents of the LDPE with starch, pro-oxidant and starch. By fractionated Py-GC-MS at 400 and 500 degreesC, acetaldehyde, acrylic acid, lactoyl acrylic acid, two lactide isomers and cyclic oligomers up to pentamer were identified in poly(lactide) (PLA). The ratio of meso-lactide to D, L-lactide was lower in the biotically hydrolysed PLA, while the PLA matrices changes of unaged and chemically hydrolysed samples gave quite similar pyrograms. Thus, the most severly thermo-oxidised LDPE-sample had in a large peak at the C-9 fragment opposite to the other LDPE-samples while the most severly hydrolysed PLA (biotically hydrolysed) had a ratio of meso-lactide to D,L-lactide quite different from unaged and chemically hydrolysed sample.

  • 244.
    Westphal, Corinna
    KTH, Superseded Departments, Polymer Technology.
    PLA a biodegradable and renewable material with potential use in the sustainable society1998Licentiate thesis, comprehensive summary (Other scientific)
  • 245.
    Wiberg, Göran
    KTH, Superseded Departments, Polymer Technology.
    Devlopment and relaxation of orientation in liquid crystalline polymers: transport properties of liquid crystalline polymer blends1997Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    In this thesis different types of liquid crystallinepolymers have been investigated with respect to build up andrelaxation of orientation. The potential of making new barriermaterials using liquid crystalline polymer blends was alsostudied. Studies on the relaxation of orientation in injectionmoulded Vectra were performed by subjecting samples ofdifferent degrees of orientations to various thermal treatmentsand different clamping procedures of the sample. Theorientation was assessed by infrared spectroscopy andX-raydiffraction. The oriented samples showed, depending on thethermo-mechanical history, either an increase or a decrease inchain orientation on annealing above and below the crystalmelting range. Highhly oriented samples with ability to changetheir shapes during annealing relaxed quickly from a Hermansorientanon parameter value. f~0.5. to a universal value off~0.2-0.3 at temperatures above 290(C. whereas increasedorientation was obtained for samples with low orientation giventhe same treatment. Slow and gradual heating favoured retainedor increased orientation which persisted far above the meltingregion. It is proposed that this is due to solid staterecrystallization from pseudohexagonal crystals to more stableorthorhombic crystals and to crystal modification II ofpoly(hydroxybenzoic acid). Built-in stresses in injectionmoulded specimens caused curling and shrinkage in orientedsamples at temperatures above 200(C. This behaviour wascorrelated with a noisy baseline and artificial endothermicpeaks during a first heating scan in a differential scanningcalorimeter(DSC). A more reliable method with greatly improvedreproducibility of the heating curves involved either immersionof the sample in silicon oil or placing the sample betweenKapton sheets. This allowed free shrinkage and secured goodthermal contact between the sample and the sample pan. Shearinduced orientation and relaxation of orientation in Vectra wasstudied in a thermo-optical shear cell. The transmitted lightintensity through crossed polarizers increased with increasingshear rate and increasing temperature. Rapid relaxation wasdetected after cessation ofshear at high shear rates. The shortrelaxation times prevented consersation of any appreciabledegrees of orientation by quenching after shearing. Samplessheared and cooled simultaneously showed a high degree oforientation (f~0.7). Infrared rheometry was used to study asmectic side-chain polymer. Steady shear induced a high degreeof perpendicular orientation of the mesogens (f~-0.3). Therelaxation of orientation was slow and not complete after 15h.A lyotropic system of hydroxypropylcellulose in m-cresol wasalso studied using infrared rheomety.Studies reported in theliterature of the molecular orientation for sheared lyotropicsystems have yielded contradictory results. in this work a highorder parameter was achieved in a 50( solution (f~0.55) whereaslower values were obtained in d 45% solution. The relaxationwas in most cases complete within 10 minutes after cessation ofshear. In some cases. After complete relaxation, the orderincreased considerably. Small additions of a liquid crystallinepolymer to a thermoplastic flexible-chain matrix often leads toimproved properties. Transport properties of methanol inVectra/Polyethersulphone blends were investigated with respectto composition.processing technique and orientation. The datawere fitted to a model based on concentration dependentdiffusion. The solubility decreased linearly with LCP content.The zero concentration diffusity was lowest for the compressionmoulded samples where the LCP component formed a continuousphase at lower LCP contents compared to the injection mouldedsamples.

    Kewords:liquid crystalline polymer; thermotropic;lyotropic; copolyester; Vectra; infrared spectroscopy;orientation; relaxation; thermal behaviour; blends; transportproperties

  • 246. Yousefi, H.
    et al.
    Wiberg, G.
    Skytt, M. L.
    Magda, J. J.
    Gedde, Ulf W.
    KTH, Superseded Departments, Polymer Technology.
    Development and relaxation of orientation in sheared concentrated lyotropic solutions of hydroxypropylcellulose in m-cresol2003In: Polymer, ISSN 0032-3861, E-ISSN 1873-2291, Vol. 44, no 4, p. 1203-1210Article in journal (Refereed)
    Abstract [en]

    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.

  • 247.
    Yousefi, Homa
    KTH, Superseded Departments, Polymer Technology.
    Transport properties and rheological properties of polymers with special molecular architecture2001Licentiate thesis, comprehensive summary (Other scientific)
  • 248.
    Örtegren, Jonas
    KTH, Superseded Departments, Polymer Technology.
    Liquid crystalline polymers for nonlinear optics: pyroelectric polymers and ferroelectric dendrimers2001Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    This thesis deals with liquid crystalline materialsincluding monomers, side-chain polymers, crosslinked polymers,and dendrimers. The materials are pyroelectric, meaning thatthere is a macroscopic electric polarization in the material,which is energetically stable in the absence of externalfields. The energetically stable, or spontaneous, polarizationmakes the material suitable for second-order nonlinear optics(NLO). Examples of second order NLO processes are secondharmonic generation (SHG), optical parametric amplification,and processes involving modulations of the refractive indices.In isotropic polymeric systems, the material is made secondorder NLO active by applying an electric field at hightemperatures, thereby inducing polar order, and by cooling toroom temperature with the field applied. The polarization isthereby "locked-in" into the polymer, and the material issecond-order NLO active. Such systems often loose polar order,and thereby second order NLO response, quite rapidly. The polarorder in pyroelectric materials is however energeticallystable, and one may therefore expect better time-dependentsecond order NLO properties in these materials. In this work,pyroelectric polymers were prepared by photopolymerization ofsurface stabilized ferroelectricliquid crystals. Thephotopolymerized material showed a clear second order NLOresponse, as measured by SHG, also in the absence of anexternal electric field. The d23-coefficient was 0.25 pm V-1. Furthermore, the pyroelectric polymers werestable at room temperature for approximately 50 days. In orderto improve the thermal stability of the polymers, a crosslinkedpolymer system was prepared, which exhibited improved thermalstability, compared to the uncrosslinked polymers. Thecrosslinked polymers were unaffected by aging at 130°C forseveral hours. The thermal stability of the polymers wasfurther analyzed by a pyroelectric technique. The largestestimated pyroelectric coefficient was 2 nC cm-2K-1. The crosslinked polymer showed a weak but clearpyroeletric response even after being heated to 260 °C.Novel liquid crystalline dendrimers of different generationwere also studied. The dendrimers were ferroelectric, meaningthat there are two stable polarization states in the material,and that the polarization may be reversed by application of anelectric field. The dendrimers showed a slightly lower value ofspontaneous polarization than their low molar mass analogue.The spontaneous polarization of the LC dendrimers wasapproximately 40 nC cm-2, and was basically independent of the generationnumber of the dendrimer. A clear, but rather small SHG responsewas recorded in these systems. By incorporating a nitro-groupin the mesogen of the LC dendrimer, the d23- coefficient of the second order NLO responsecould be improved by a factor 3, to 0.03 pm V-1. This thesis gives an introduction topyroelectricity, ferroelectricity, and linear and nonlinearoptical effects in materials. It further contains descriptionsof various techniques that were used to characterize the novelliquid crystalline materials. It discusses the results from themeasurements and the properties of the liquid crystallinematerials, with focus on second order NLO.

  • 249.
    Östmark, E
    et al.
    KTH, Superseded Departments (pre-2005), Fibre and Polymer Technology.
    Harrisson, S
    Hult, Anders
    KTH, Superseded Departments (pre-2005), Polymer Technology.
    Wooley, K L
    Hawker, C J
    Malmström, Eva
    KTH, Superseded Departments (pre-2005), Polymer Technology.
    Modification of hydroxyethyl cellulose using dendrons or ATRP. Template for molecular rods?2004In: Abstracts of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 228, p. U437-U437Article in journal (Other academic)
2345 201 - 249 of 249
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