Cannavacciuolo, Felicia Daniela (2021) A Smart HTE Approach to Sustainable Polyolefin Materials. [Tesi di dottorato]

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There is little doubt that High Throughput Experimentation (HTE) will ultimately become the gold standard of chemical R&D. On the other hand, until now the technical complexity and high Capex and Opex of HTE tools and methods have hampered a broad dissemination in several important areas of the chemical sciences. In particular, HTE approaches to organometallic catalysis began to spread in academia only recently. The general aim of the present PhD project was to implement and apply 'smart' HTE protocols for tackling complex problems in olefin polymerization catalysis, with special focus on polyolefin sustainability. The main case history was Coordinative Chain Transfer Polymerization (CCTP) and its Chain Shuttling Polymerization (CSP) variant: unraveling the complex kinetics governing this elusive chemistry and expanding its scope to novel monomers and materials are important open challenges. We have also addressed questions of relevance for the recycling of polyolefin wastes in the context of a circular economy. The HTE toolkit is introduced in Chapter 2. Despite the extensive robotic automation, a HTE platform is not a push-button setup. A complete HTE workflow can include several reaction platforms and an array of integrated analytical tools amenable to high-throughput operation and yet ensuring the precision and accuracy of conventional high-end tools. Chapter 3 illustrates the implementation of HTE protocols for parallel olefin CSP experiments. We successfully downscaled the high-temperature and high-pressure synthesis of statistical Olefin Block Copolymers (OBC) according to the Dow InfuseTM technology. A systematic exploration of the multi-dimensional variables hyperspace of ethene/1-alkene copolymerization under tandem catalysis conditions led us to elucidate unambiguously for the first time the microstructure and architecture of these advanced materials, that found commercial applications as unique thermoplastic elastomers and also as effective phase compatibilizers in immiscible polyolefin blends. Chapter 4 illustrates a systematic and thorough search for catalyst systems amenable to CCTP/CSP other than those originally introduced by Dow Chemical. Notwithstanding the several claims in the literature, our study led us to conclude that reversible trans-alkylation in catalytic olefin polymerizations is exceedingly rare, and therefore expanding the scope of CSP via catalyst diversification is problematic. Moving from this negative conclusion, in Chapter 5 we explored the alternative option of OBC diversification by using unconventional comonomers. Two new classes of OBCs were prepared by CSP of ethene with 4-methyl-1-pentene or 1-hexadecene, respectively. Both comonomers are expected to provide block copolymers with unusual and interesting physical properties. In Chapter 6 we report how the HTE workflow was utilized to explore the possibility to introduce a fluorescent tag into polyethylene and polypropylene chains via copolymerization, for diagnostic purposes. The idea was to make different polyolefin grades identifiable post-mortem with a simple, cheap and fast optical measurement. Series of ethene and propene copolymerizations with 1-pyrenylheptene, a fluorescent comonomer prepared ad hoc, demonstrated that the concept works very well down to incorporations of the tag at which the thermal and physico-mechanical properties of the copolymers are practically identical to those of the corresponding homopolymers. Chapter 7 investigates catalytic depolymerization as a possible route of polymer waste recycling. It has long been known that polyolefin can be cleaved under comparatively mild conditions in the presence of certain heterogeneous transition metal catalysts. Recently, this has also been shown for polydienes with a homogeneous catalyst. In the framework of the present thesis we explored the depolymerization of 1,4-cis-polybutadiene mediated by a large library of Group 4 metallocene and post-metallocene complexes. A strong dependence of molecular kinetics on catalyst structure was highlighted, and efficient catalysts were identified. This part of the project was a collaboration with Prof. Adam S. Veige at the University of Florida (Gainesville, FL). From the conclusions of the project, which are summarized in Chapter 8, it is well evident that 'smart' HTE methodologies are ideally suited to rapidly identify novel and convenient routes of olefin polymerization and polyolefin/polydiene depolymerization that can improve the sustainability of these ubiquitous and important industrial processes and materials, making them ultimately better suited to a circular economy.

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