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Understanding the mechanisms behind atom transfer radical polymerization: exploring the limit of control
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
2011 (English)Doctoral thesis, comprehensive summary (Other academic)
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.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology , 2011. , 64 p.
Series
Trita-CHE-Report, ISSN 1654-1081 ; 2011:021
Keyword [en]
polymerization, controlled radical polymerization, atom transfer radical polymerization, kinetics, catalysis, electrochemistry
National Category
Polymer Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-32104ISBN: 978-91-7415-933-2OAI: oai:DiVA.org:kth-32104DiVA: diva2:408884
Public defence
2011-04-29, Sal K2, Teknikringen 28, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
Swedish Research Council, 621-2005-6190
Note
QC 20110406Available from: 2011-04-06 Created: 2011-04-06 Last updated: 2011-04-13Bibliographically approved
List of papers
1. Heterogeneous iron(II)-chloride mediated radical polymerization of styrene
Open this publication in new window or tab >>Heterogeneous iron(II)-chloride mediated radical polymerization of styrene
2009 (English)In: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, Vol. 306, no 1-2, 69-76 p.Article in journal (Refereed) Published
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.

Keyword
Atom transfer radical polymerization (ATRP), Heterogeneous, Iron chloride, Kinetics, Polystyrene
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-18528 (URN)10.1016/j.molcata.2009.02.024 (DOI)000267084900011 ()2-s2.0-67349222833 (ScopusID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2011-04-06Bibliographically approved
2. Solvent Effects on ATRP of Oligo(ethylene glycol) Methacrylate. Exploring the Limits of Control
Open this publication in new window or tab >>Solvent Effects on ATRP of Oligo(ethylene glycol) Methacrylate. Exploring the Limits of Control
2009 (English)In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 42, no 9, 3302-3308 p.Article in journal (Refereed) Published
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.

Keyword
TRANSFER RADICAL POLYMERIZATION; PROPAGATION RATE COEFFICIENTS; ACTIVATION RATE CONSTANTS; METHYL-METHACRYLATE; AMBIENT-TEMPERATURE; AQUEOUS-MEDIA; COMPLEXES; STYRENE; COPPER; COUNTERION
Identifiers
urn:nbn:se:kth:diva-18388 (URN)10.1021/ma8028425 (DOI)000265781300012 ()2-s2.0-66549102560 (ScopusID)
Note
QC 20100525Available from: 2010-08-05 Created: 2010-08-05 Last updated: 2011-04-06Bibliographically approved
3. Investigation of iron complexes in ATRP: Indications of different iron species in normal and reverse ATRP
Open this publication in new window or tab >>Investigation of iron complexes in ATRP: Indications of different iron species in normal and reverse ATRP
2011 (English)In: Journal of Molecular Catalysis A: Chemical, ISSN 1381-1169, Vol. 346, no 1-2, 20-28 p.Article in journal (Refereed) Published
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.

Keyword
Atom transfer radical polymerization (ATRP), Electrochemistry, Iron catalyst, Kinetics
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-32102 (URN)10.1016/j.molcata.2011.06.001 (DOI)000294694500003 ()2-s2.0-80051585641 (ScopusID)
Funder
Swedish Research Council, 621-2005-6190
Note
QC 20110406. Updated from manuscript to article in journal.Available from: 2011-04-06 Created: 2011-04-06 Last updated: 2012-08-22Bibliographically approved
4. Investigation of the ATRP process through simulations - predicting the limit of control
Open this publication in new window or tab >>Investigation of the ATRP process through simulations - predicting the limit of control
(English)Manuscript (preprint) (Other academic)
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.

Keyword
atom transfer radical polymerization, catalysis, simulations, kinetics
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-32103 (URN)
Funder
Swedish Research Council, 621-2005-6190
Available from: 2011-04-06 Created: 2011-04-06 Last updated: 2011-04-06Bibliographically approved

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