Endre søk
Begrens søket
1 - 10 of 10
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Treff pr side
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
  • Standard (Relevans)
  • Forfatter A-Ø
  • Forfatter Ø-A
  • Tittel A-Ø
  • Tittel Ø-A
  • Type publikasjon A-Ø
  • Type publikasjon Ø-A
  • Eldste først
  • Nyeste først
  • Skapad (Eldste først)
  • Skapad (Nyeste først)
  • Senast uppdaterad (Eldste først)
  • Senast uppdaterad (Nyeste først)
  • Disputationsdatum (tidligste først)
  • Disputationsdatum (siste først)
Merk
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 1.
    Bergenudd, Helena
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Investigation of the ATRP process through simulations - predicting the limit of controlManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    The limit for when a well controlled atom transfer radical polymerization (ATRP) system can be obtained is described based on the results from kinetic simulations where the ATRP equilibrium constant, KATRP, is varied and the rates and degree of control in different ATRP systems are evaluated. The apparent rate constant, kpapp, increases with increasing KATRP, but a maximum is reached where after kpapp decreases as the result of a large degree of initial terminations due to the strong shift of the equilibrium towards the active species. Before the maximum is reached as KATRP is increased, the limit of control is passed, i.e. when KATRP is increased further, apparent first order kinetics and well controlled molecular weights will no longer be obtained. The equilibrium constant at which the limit of control is reached varies linearly with the propagation rate constant. This enables the design of well controlled ATRP systems based on the knowledge of the propagation rate constant and KATRP. The influence of the conversion and chain length dependence of the termination rate constant on the simulation results is also discussed. The kpappKATRP trend shown in the simulations is confirmed by comparing with previous experimental results.

  • 2.
    Bergenudd, Helena
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Understanding the mechanisms behind atom transfer radical polymerization: exploring the limit of control2011Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    Atom transfer radical polymerization (ATRP) is one of the most commonly employed techniques for controlled radical polymerization. ATRP has great potential for the development of new materials due to the ability to control molecular weight and polymer architecture. To fully utilize the potential of ATRP as polymerization technique, the mechanism and the dynamics of the ATRP equilibrium must be well understood.

    In this thesis, various aspects of the ATRP process are explored through both laboratory experiments and computer modeling. Solvent effects, the limit of control and the use of iron as the mediator have been investigated. It was shown for copper mediated ATRP that the redox properties of the mediator and the polymerization properties were significantly affected by the solvent. As expected, the apparent rate constant (kpapp) increased with increasing activity of the mediator, but an upper limit was reached, where after kpapp was practically independent of the mediator potential. The degree of control deteriorated as the limit was approached.

    In the simulations, which were based on the thermodynamic properties of the ATRP equilibrium, the same trend of increasing kpapp with increasing mediator activity was seen and a maximum was also reached. The simulation results could be used to describe the limit of control. The maximum equilibrium constant for controlled ATRP was correlated to the propagation rate constant, which enables the design of controlled ATRP systems.

    Using iron compounds instead of copper compounds as mediators in ATRP is attractive from environmental aspects. Two systems with iron were investigated. Firstly, iron/EDTA was investigated as mediator as its redox properties are within a suitable range for controlled ATRP. The polymerization of styrene was heterogeneous, where the rate limiting step is the adsorption of the dormant species to the mediator surface. The polymerizations were not controlled and it is possible that they had some cationic character.

    In the second iron system, the intention was to investigate how different ligands affect the properties of an ATRP system with iron. Due to competitive coordination of the solvent, DMF, the redox and polymeri­zation properties were not significantly affected by the ligands. The differences between normal and reverse ATRP of MMA, such as the degree of control, were the result of different FeIII speciation in the two systems.

  • 3.
    Bergenudd, Helena
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Coullerez, Geraldine
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Jonsson, Mats
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Malmström, Eva E.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Solvent Effects on ATRP of Oligo(ethylene glycol) Methacrylate. Exploring the Limits of Control2009Inngår i: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 42, nr 9, s. 3302-3308Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Five copper complexes in combination with six monomer-solvent mixtures have been used to investigate the solvent effects oil ATRP of oligo(ethylene glycol) methacrylate (OEGMA). The redox properties of the copper complexes in OEGMA-solvent mixtures and the apparent rate constants (k(p)(app)) for ATRP of OEGMA were correlated to the degree of control over the polymerizations. Based on this correlation, a general discussion of the limits of control in ATRIP is carried out. One of the key parameters for control in ATRP is the propagation rate constant, making the choice of monomer essential for the design of ail ATRP system. Also, the solvent effects oil the ATRP equilibrium constant (K-ATRP) affect the limit of control (i.e., the apparent rate constant above which control is lost). The choice of copper complex is also more important than the choice of solvent for the design of a well-controlled ATRP system.

  • 4.
    Bergenudd, Helena
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi (stängd 20110630).
    Jonsson, Mats
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi (stängd 20110630).
    Malmström, Eva
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Investigation of iron complexes in ATRP: Indications of different iron species in normal and reverse ATRP2011Inngår i: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 346, nr 1-2, s. 20-28Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In an attempt to correlate the ATRP kinetics and the redox properties of the mediator, eight iron complexes with nitrogen, phosphorous and carboxylic acid containing ligands were investigated by electrochemical measurements and by using them as mediators in normal and reverse ATRP of MMA in DMF. The redox properties of the iron complexes in DMF, measured by cyclic voltammetry, did not differ significantly, which was reflected in the ATRP kinetics as the apparent rate constants were practically the same with all the complexing ligands. The degree of control over the polymerization was, however, much improved in reverse ATRP as compared to normal ATRP. In this ATRP system, the ligand type is not crucial for the redox or polymerization properties. Several observations indicate that the iron species in the two systems were not the same, the Fe(III) species resulting from oxidation of Fe(II) in normal ATRP is different from the starting Fe(III) species in reverse ATRP.

  • 5.
    Bergenudd, Helena
    et al.
    KTH, Skolan för kemivetenskap (CHE).
    Jonsson, Mats
    KTH, Skolan för kemivetenskap (CHE).
    Malmström, Eva
    KTH, Skolan för kemivetenskap (CHE).
    POLY 104-Predicting the level of control for ATRP systems2009Inngår i: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 238Artikkel i tidsskrift (Annet vitenskapelig)
  • 6.
    Bergenudd, Helena
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Jonsson, Mats
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Malmström, Eva
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Predicting the Limit of Control in the ATRP Process: Results from Kinetic Simulations2011Inngår i: Macromolecular Theory and Simulations, ISSN 1022-1344, E-ISSN 1521-3919, Vol. 20, nr 9, s. 814-825Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Kinetic simulations are reported, where the ATRP equilibrium constant K(ATRP) is varied and the rates and degree of control in different ATRP systems are evaluated. The apparent rate constant k(app) increases with increasing K(ATRP), but a maximum is reached. The limit of control is passed before the maximum, i.e. when K(ATRP) is increased further, apparent first-order kinetics and well-controlled molecular weights will no longer be obtained. The equilibrium constant at which the limit of control is reached varies linearly with the propagation rate constant. This enables the design of well controlled ATRP systems. The influence of the conversion and chain length dependence of the termination rate constant on the simulation results is discussed.

  • 7.
    Bergenudd, Helena
    et al.
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Jonsson, Mats
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Nyström, Daniel
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Malmström, Eva
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Heterogeneous iron(II)-chloride mediated radical polymerization of styrene2009Inngår i: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, E-ISSN 1873-314X, Vol. 306, nr 1-2, s. 69-76Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In an attempt to perform atom transfer radical polymerization (ATRP) with a more environmentally friendly mediator, polymerization of styrene in the presence of iron(II)-chloride and EDTA was explored from a mechanistic point of view. The presence of EDTA, which normally can form a complex with FeCl2, had no influence on the polymerization results as both the mediator and EDTA were insoluble in the polymerization medium. A mechanism is suggested for the heterogeneous polymerization of styrene mediated by iron (II)-chloride in p-xylene at 50 °C. Varying the mediator amount more than 10-fold revealed that the rate limiting step at low mediator amounts was the adsorption of the initiator or dormant polymer to the mediator surface, whereas at higher mediator amounts, the rate limiting step was instead the activation step in the ATRP equilibrium. The mechanism changed to free radical polymerization in solution at a certain conversion, resulting in lower apparent rate constant and an increased amount of transfer and termination reactions. Chain extension with MMA showed that a significant proportion of the polymer chain ends were active also at high conversions.

  • 8.
    Hansson, Susanne
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Antoni, Per
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Bergenudd, Helena
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Malmström, Eva
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Assessing initiator content by cleavage of polymers grafted via ARGET ATRP2011Inngår i: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 242Artikkel i tidsskrift (Fagfellevurdert)
  • 9.
    Hansson, Susanne
    et al.
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Antoni, Per
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Bergenudd, Helena
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Malmström, Eva
    KTH, Skolan för kemivetenskap (CHE), Fiber- och polymerteknik.
    Selective cleavage of polymer grafts from solid surfaces: assessment of initiator content and polymer characteristics2011Inngår i: POLYM CHEM, ISSN 1759-9954, Vol. 2, nr 3, s. 556-558Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A novel initiator for atom transfer radical polymerization, also allowing for selective cleavage of polymer grafts, was designed and immobilized on a solid substrate. After cleavage, the initiator content was determined by utilizing Ellman's reagent and the cleaved polymer grafts were isolated and characterized by size exclusion chromatography.

  • 10. Kumar, Sangit
    et al.
    Johansson, Henrik
    Kanda, Takahiro
    Engman, Lars
    Muller, Thomas
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Bergenudd, Helena
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Jonsson, Mats
    KTH, Skolan för kemivetenskap (CHE), Kemi, Kärnkemi.
    Pedulli, Franco
    Amorati, Riccardo
    Valgimigli, Luca
    Catalytic Chain-Breaking Pyridinol Antioxidants2010Inngår i: Journal of Organic Chemistry, ISSN 0022-3263, E-ISSN 1520-6904, Vol. 75, nr 3, s. 716-725Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The synthesis of 3-pyridinols carrying alkyltelluro, alkylseleno, and alkylthio groups is described together with a detailed kinetic, thermodynamic, and mechanistic Study of their antioxidant activity. When assayed for their capacity to inhibit azo-initiated peroxidation of linoleic acid in a water/chlorobenzene two-phase system, tellurium-containing 3-pyridinols were readily regenerable by N-acetylcysteine contained in the aqueous phase. The best inhibitors quenched peroxyl radicals more efficiently than alpha-tocopherol, and the duration of inhibition was limited only by the availability of the thiol reducing agent. fn homogeneous phase, inhibition of styrene autoxidation absolute rate constants k(inh) for quenching of peroxyl radical were as large as 1 x 10(7) M-1 s(-1), thus Outperforming the best phenolic antioxidants including alpha-tocopherol. Tellurium-containing 3-pyridinols could be quantitatively regenerated in homogeneous phase by N-tert-butoxycarbonyl cysteine methyl ester, a lipid-soluble analogue of N-acetylcysteine. In the presence of an excess of the thiol, a catalytic mode of action was observed, similar to the one in the two-phase system. Overall, compounds bearing the alkyltelluro moiety ortho to the OH group were much more effective antioxidants than the corresponding para isomers. The origin of the high reactivity of these compounds was explored using pulse-radiolysis thermodynamic measurements, and a mechanism for their unusual antioxidant activity was proposed. The tellurium-containing 3-pyridinols were also found to catalyze reduction of hydrogen peroxide in the presence of thiol reducing agents, thereby acting as multifunctional (preventive and chain-breaking) catalytic antioxidants.

1 - 10 of 10
RefereraExporteraLink til resultatlisten
Permanent link
Referera
Referensformat
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annet format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annet språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf