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Investigation of the ATRP process through simulations - predicting the limit of control
KTH, School of Chemical Science and Engineering (CHE), Chemistry, Nuclear Chemistry.
(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 [en]
atom transfer radical polymerization, catalysis, simulations, kinetics
National Category
Polymer Chemistry
Identifiers
URN: urn:nbn:se:kth:diva-32103OAI: oai:DiVA.org:kth-32103DiVA: diva2:408878
Funder
Swedish Research Council, 621-2005-6190
Available from: 2011-04-06 Created: 2011-04-06 Last updated: 2011-04-06Bibliographically approved
In thesis
1. Understanding the mechanisms behind atom transfer radical polymerization: exploring the limit of control
Open this publication in new window or tab >>Understanding the mechanisms behind atom transfer radical polymerization: exploring the limit of control
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
polymerization, controlled radical polymerization, atom transfer radical polymerization, kinetics, catalysis, electrochemistry
National Category
Polymer Chemistry
Identifiers
urn:nbn:se:kth:diva-32104 (URN)978-91-7415-933-2 (ISBN)
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

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