Kinetics of free radical homo- and copolymerisations investigated with pulsed laser methods
by Enno Meyer
Date of Examination:2024-02-08
Date of issue:2024-03-06
Advisor:Prof. Dr. Philipp Vana
Referee:Prof. Dr. Philipp Vana
Referee:Prof. Dr. Thomas Zeuch
Persistent Address:
http://dx.doi.org/10.53846/goediss-10392
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Abstract
English
Free-radical polymerisation is the most important polymerisation process due to its simplicity and robustness. It is therefore necessary to understand the kinetics of the involved reactions in order to plan a polymerisation, be it on lab scale or industrial scale. Three different topics are investigated in this thesis: First, the copolymerisation of styrene (Sty) with maleic anhydride (MAn) which is interesting from a kinetic standpoint because MAn does not homopolymerise. Thus, several reaction steps can be neglected and the kinetic treatment is simplified. By using the Single–pulse pulsed–laser–polymerisation with EPR spectroscopy (SP–PLP–EPR) technique developed by Buback, hitherto unknown chain-length dependent termination rate coefficients can be extracted. However, it as not possible to investigate this system with SP–PLP–EPR due to a to small signal-to-noise ratio (S/N). However some preliminary calculations had been performed which are shown. Second, since petrol-based monomers are not sustainable, bio-based alternatives are of great interest. A well-known bio-based monomer family is itaconic acid and its corresponding esters. The propagation and termination kinetics of a few of the homologues have been already investigated in earlier publications. However, for the diethyl and di-n-propyl ester no data exist. Consequently, this gap was closed by measuring the propagation rate coefficient with Pulsed laser polymerisation–size exclusion chromatography (PLP–SEC) and the chain-length dependent termination rate coefficent with the already mentioned SP–PLP–EPR methods. Both rate coefficients were determined for a range of temperatures. The third topic deals with the kinetics of copolymerisations and a rarely investigated property of copolymerisations, the propagating radical fraction (PRF) which describes the composition of radical functionalities during a copolymerisation. This observable was measured for three different copolymerisation systems with stationary EPR spectroscopy and subsequent fitting of the copolymerisation EPR spectra with easyspin. The equation describing the PRF was fitted to obtain kinetic parameters. This yielded unplausible results. Consequently, a new data evaluation method, called ‘determining reactivity ratios with a conjoined scalable fit (DRACO)’, was created which combines the kinetic information of multiple observables in order to make the results more reliable. In this case, the composition of the final copolymer, the overall propagation rate coefficient ⟨kp⟩ and the previously described PRF were used. The method finds kinetic parameters which describe the combination of all observables best instead of the still widespread practice of fitting each property separately. DRACO can be easily adapted to include other or more observables. The version developed in this work can use the explicit penultimate model, the implicit penultimate model or the terminal model, but other models can be easily implemented. This approach yielded plausible results which can now be considered the new best values.
Keywords: polymerisation; free-radical; copolymerisation; propagation; termination; SP-PLP-EPR; PLP-SEC; modelling; EPR
