title: Immobilization and Kinetics of Wolf-Lamb type catalysts through electrospun membranes and printed structures
Creators: name: Pretscher, Martin O.
Publisher: name: University of Bayreuth
Year: 2021
Subjects: subject: Wolf-Lamm Katalyse
subject: Säure-Base
subject: ein-Topf Reaktion
subject: Elektrospinnen
subject: 3D Druck
subject: Kinetik
subject: 540

description: Wolf-Lamb type catalysts are mutually incompatible catalysts. Hence, to use such catalysts within a multi-step one-pot reaction, immobilization through site-isolation of the catalysts is necessary to protect them from each other. Through such immobilization, reaction sequences can be catalysed which otherwise would not be available without an intermediate purification step. The existing Wolf-Lamb type carrier systems contain tri-block copolymeric core-shell micelles, star polymers or inorganic particles which utilise multi-step procedures or procedures valid only for two-step catalysts. In this thesis, it is the aim to study new recyclable carrier systems of these Wolf-Lamb type catalysts, which are easy to prepare and can be used in one-pot reactions in a modular way. Within the first step, model systems were investigated based on the acidic copolymer poly(styrene-co-styrene sulfonic acid-co-methacryl benzophenone) and the basic copolymer poly(styrene-co-4-vinylpyridine-co-methacryl benzophenone) for the use in the one-pot two-step, deacetylation of dimethoxybenzyl to benzaldehyde followed by a carbon building reaction with ethylcyanoformate to cyano(phenyl)methyl ethyl carbonate. The polymeric catalysts were processed to self-standing materials by either electrospinning to porous membranes or 2D printing on a neutral mesh substrate. The polymer acid and base catalyst were prepared in high molecular masses, which is required for processing, by free-radical polymerization of styrene, styrene sulfonic acid (for acidic catalyst) or 4-vinylpyridine (for basic copolymer) and methacryl benzophenone (crosslinking agent). The resulting two-step kinetics were investigated by fitting of the underlying differential equations. For the electrospun membranes, it was determined that the acidic copolymer needed to be processed as the polymeric salt (poly(styrene-co-sodium styrene sulfonate-co-methacryl benzophenone)) as otherwise the activity of the catalyst was reduced due to salt formation during the process. The catalytic membranes were photo-crosslinked with UV-light and the acidic membrane protonated by addition of hydrochloric acid in methanol. The system worked for the two-step reaction and a yield of 95% for the first step and 80% within 360 minutes was achieved. The kinetic studies showed that a parameter Δt needed to be implemented as the second step had a significant retarded start as it only started after enough benzaldehyde was available. As electrospinning is a complex process, which is influenced by 15 different internal and external parameters, a simpler method was tested with 2D printing. An advantage of this method was, that it is possible to directly print the acidic catalyst and it was not necessary to protonate it after processing. The results were comparable towards the electrospinning process. A yield of 95% for the first step and around 65% for the second step, but within a shorter time frame of only 240 minutes. The lower conversion within the second step can be due to the low basicity of 4-vinylpyridine and possible due to the bulkier structure. The fitted kinetics showed that the parameter Δt is also necessary and the second reaction step is the speed determining step. Through these investigations, it was shown that both systems were promising. Therefore, more in-depth studies were necessary to establish whether electrospinning or 2D printing is the more useful system. To further broaden possible applications, the basic polymer was changed towards poly(styrene-co-4-vinylbenzylamine-co-N-(4-benzoylphenyl)acrylamide). This specific polymer is not directly available through free radical polymerization, which makes it an ideal candidate to further research the possibilities of post-processing treatment to develop further modular systems in the future. N-(4-vinylbenzyl)phtalimide is a possible candidate, as it can be easily modified to the primary amine by a reaction with hydrazine. It was shown that the treatment with hydrazine influenced the stability of the structures neither for the printed nor for the electrospun system. As a reaction the deacetylation reaction of dimethoxybenzyl to benzaldehyde followed by a basic catalysed Knoevenagel reaction with ethyl cyanoacetate to ethyl-2-cyano-3-phenylacrylate in toluene was used. The catalytic studies showed that the 2D printed structures lead to faster reactions. The kinetical studies showed a decrease of the parameter Δt within these systems and the reaction rate was 10 times higher for the first step and 5 times higher for the second step reaction. While it is surprising at first, as electrospun materials show a higher surface area, it is explainable through the swelling of the substances leading to better mass transport throughout the system and the reachability of the functional groups is improved within printed structures.